build(rechner): exact expression engine, keypad, scientific panel, history, memory; README

Co-Authored-By: Claude Opus 5.5 <[email protected]>

README.md

@@ -8,6 +8,7 @@
 
 | App | Replaces | Status | Install |
 | --- | --- | --- | --- |
+| **Rechner** (`rechner/`) | Google Calculator | alpha | [Obtainium](https://apps.obtainium.imranr.dev/redirect?r=obtainium://app/%7B%22id%22%3A%22app.rechner%22%2C%22url%22%3A%22https%3A%2F%2Fgit.mrblake.cc%2FMrBlake%2FNoGooleApps%22%2C%22author%22%3A%22MrBlake%22%2C%22name%22%3A%22Rechner%22%2C%22overrideSource%22%3A%22Codeberg%22%2C%22preferredApkIndex%22%3A0%2C%22additionalSettings%22%3A%22%7B%5C%22appId%5C%22%3A%5C%22app.rechner%5C%22%2C%5C%22includePrereleases%5C%22%3Atrue%2C%5C%22fallbackToOlderReleases%5C%22%3Atrue%2C%5C%22filterReleaseTitlesByRegEx%5C%22%3A%5C%22%5ERechner%20%5C%22%2C%5C%22apkFilterRegEx%5C%22%3A%5C%22%5Erechner-.%2A%5C%5C%5C%5C.apk%24%5C%22%2C%5C%22autoApkFilterByArch%5C%22%3Afalse%2C%5C%22verifyLatestTag%5C%22%3Afalse%2C%5C%22releaseTitleAsVersion%5C%22%3Afalse%7D%22%7D) · F-Droid: not yet |
 | **Uhr** (`uhr/`) | Google Clock / Pixel Clock | alpha, in daily testing | [Obtainium](https://apps.obtainium.imranr.dev/redirect?r=obtainium://app/%7B%22id%22%3A%22app.uhr%22%2C%22url%22%3A%22https%3A%2F%2Fgit.mrblake.cc%2FMrBlake%2FNoGooleApps%22%2C%22author%22%3A%22MrBlake%22%2C%22name%22%3A%22Uhr%22%2C%22overrideSource%22%3A%22Codeberg%22%2C%22preferredApkIndex%22%3A0%2C%22additionalSettings%22%3A%22%7B%5C%22appId%5C%22%3A%5C%22app.uhr%5C%22%2C%5C%22includePrereleases%5C%22%3Atrue%2C%5C%22fallbackToOlderReleases%5C%22%3Atrue%2C%5C%22filterReleaseTitlesByRegEx%5C%22%3A%5C%22%5EUhr%20%5C%22%2C%5C%22apkFilterRegEx%5C%22%3A%5C%22%5Euhr-.%2A%5C%5C%5C%5C.apk%24%5C%22%2C%5C%22autoApkFilterByArch%5C%22%3Afalse%2C%5C%22verifyLatestTag%5C%22%3Afalse%2C%5C%22releaseTitleAsVersion%5C%22%3Afalse%7D%22%7D) · F-Droid: not yet |
 | **Wetter** (`wetter/`) | Google Weather / Pixel Weather | alpha, in daily testing | [Obtainium](https://apps.obtainium.imranr.dev/redirect?r=obtainium://app/%7B%22id%22%3A%22app.wetter%22%2C%22url%22%3A%22https%3A%2F%2Fgit.mrblake.cc%2FMrBlake%2FNoGooleApps%22%2C%22author%22%3A%22MrBlake%22%2C%22name%22%3A%22Wetter%22%2C%22overrideSource%22%3A%22Codeberg%22%2C%22preferredApkIndex%22%3A0%2C%22additionalSettings%22%3A%22%7B%5C%22appId%5C%22%3A%5C%22app.wetter%5C%22%2C%5C%22includePrereleases%5C%22%3Atrue%2C%5C%22fallbackToOlderReleases%5C%22%3Atrue%2C%5C%22filterReleaseTitlesByRegEx%5C%22%3A%5C%22%5EWetter%20%5C%22%2C%5C%22apkFilterRegEx%5C%22%3A%5C%22%5Ewetter-.%2A%5C%5C%5C%5C.apk%24%5C%22%2C%5C%22autoApkFilterByArch%5C%22%3Afalse%2C%5C%22verifyLatestTag%5C%22%3Afalse%2C%5C%22releaseTitleAsVersion%5C%22%3Afalse%7D%22%7D) · F-Droid: not yet |
 
@@ -43,6 +44,24 @@ A weather app with the look and feel of Pixel Weather: an animated sky that chan
 
 Requires Android 10 (API 29) or newer.
 
+### Rechner
+
+A calculator with the flow of the Pixel calculator: live result while typing, a scientific row that expands into a full panel, and the history in a sheet you pull down from the display.
+
+- **Exact arithmetic.** Numbers are decimal, not floating point: 0,1 + 0,2 is 0,3, 1 ÷ 3 × 3 is 1, 100! is exact. Trigonometry snaps exact angles (sin 30° = 0,5, cos π = −1). The engine is covered by unit tests.
+- **Smart input:** one key for parentheses that opens or closes as needed, operators replace each other, implicit multiplication (2π, 3(4)), percent the way people expect (50 + 10 % = 55), unfinished input still shows a preview.
+- **Scientific:** √ π ^ ! · Deg/Rad · sin cos tan and their inverses (Inv) · e ln log · eˣ 10ˣ x².
+- **History** grouped by day, tap to reuse; copy, paste and a memory (MS/MR) from a long press on the display; wallpaper colours, light and dark.
+- **No permissions** except vibration for key feedback. No network.
+
+<p align="center">
+  <img src="docs/screenshots/rechner/S01-typing-light.png" width="200" alt="Typing with live result">
+  <img src="docs/screenshots/rechner/S02-scientific-dark.png" width="200" alt="Scientific panel">
+  <img src="docs/screenshots/rechner/S03-history-dark.png" width="200" alt="History">
+</p>
+
+Requires Android 10 (API 29) or newer.
+
 ### Uhr
 
 A clock and alarm app with the look and flow of the Pixel clock: alarms in expandable cards, world clock, several timers at once, stopwatch with laps, and a bedtime schedule.
@@ -102,6 +121,16 @@ Same setup as Wetter, with the filters `^Uhr ` (release titles) and `^uhr-.*\.ap
 obtainium://app/%7B%22id%22%3A%22app.uhr%22%2C%22url%22%3A%22https%3A%2F%2Fgit.mrblake.cc%2FMrBlake%2FNoGooleApps%22%2C%22author%22%3A%22MrBlake%22%2C%22name%22%3A%22Uhr%22%2C%22overrideSource%22%3A%22Codeberg%22%2C%22preferredApkIndex%22%3A0%2C%22additionalSettings%22%3A%22%7B%5C%22appId%5C%22%3A%5C%22app.uhr%5C%22%2C%5C%22includePrereleases%5C%22%3Atrue%2C%5C%22fallbackToOlderReleases%5C%22%3Atrue%2C%5C%22filterReleaseTitlesByRegEx%5C%22%3A%5C%22%5EUhr%20%5C%22%2C%5C%22apkFilterRegEx%5C%22%3A%5C%22%5Euhr-.%2A%5C%5C%5C%5C.apk%24%5C%22%2C%5C%22autoApkFilterByArch%5C%22%3Afalse%2C%5C%22verifyLatestTag%5C%22%3Afalse%2C%5C%22releaseTitleAsVersion%5C%22%3Afalse%7D%22%7D
 ```
 
+### Rechner
+
+[<img src="https://raw.githubusercontent.com/ImranR98/Obtainium/main/assets/graphics/badge_obtainium.png" alt="Get it on Obtainium" height="54">](https://apps.obtainium.imranr.dev/redirect?r=obtainium://app/%7B%22id%22%3A%22app.rechner%22%2C%22url%22%3A%22https%3A%2F%2Fgit.mrblake.cc%2FMrBlake%2FNoGooleApps%22%2C%22author%22%3A%22MrBlake%22%2C%22name%22%3A%22Rechner%22%2C%22overrideSource%22%3A%22Codeberg%22%2C%22preferredApkIndex%22%3A0%2C%22additionalSettings%22%3A%22%7B%5C%22appId%5C%22%3A%5C%22app.rechner%5C%22%2C%5C%22includePrereleases%5C%22%3Atrue%2C%5C%22fallbackToOlderReleases%5C%22%3Atrue%2C%5C%22filterReleaseTitlesByRegEx%5C%22%3A%5C%22%5ERechner%20%5C%22%2C%5C%22apkFilterRegEx%5C%22%3A%5C%22%5Erechner-.%2A%5C%5C%5C%5C.apk%24%5C%22%2C%5C%22autoApkFilterByArch%5C%22%3Afalse%2C%5C%22verifyLatestTag%5C%22%3Afalse%2C%5C%22releaseTitleAsVersion%5C%22%3Afalse%7D%22%7D)
+
+Filters: `^Rechner ` (release titles) and `^rechner-.*\.apk$` (APKs). Raw link:
+
+```
+obtainium://app/%7B%22id%22%3A%22app.rechner%22%2C%22url%22%3A%22https%3A%2F%2Fgit.mrblake.cc%2FMrBlake%2FNoGooleApps%22%2C%22author%22%3A%22MrBlake%22%2C%22name%22%3A%22Rechner%22%2C%22overrideSource%22%3A%22Codeberg%22%2C%22preferredApkIndex%22%3A0%2C%22additionalSettings%22%3A%22%7B%5C%22appId%5C%22%3A%5C%22app.rechner%5C%22%2C%5C%22includePrereleases%5C%22%3Atrue%2C%5C%22fallbackToOlderReleases%5C%22%3Atrue%2C%5C%22filterReleaseTitlesByRegEx%5C%22%3A%5C%22%5ERechner%20%5C%22%2C%5C%22apkFilterRegEx%5C%22%3A%5C%22%5Erechner-.%2A%5C%5C%5C%5C.apk%24%5C%22%2C%5C%22autoApkFilterByArch%5C%22%3Afalse%2C%5C%22verifyLatestTag%5C%22%3Afalse%2C%5C%22releaseTitleAsVersion%5C%22%3Afalse%7D%22%7D
+```
+
 **Releases.** Every app is published as a release titled `<App> <version>` (for example `Wetter 0.1.0`, tag `wetter-v0.1.0`) with one asset named `<app>-<version>.apk`. Obtainium shows *"no matching version"* until the first release of an app exists.
 
 **F-Droid:** not available yet. The apps contain no proprietary libraries, so an F-Droid build is planned (either the main repository or a self-hosted F-Droid repo).
@@ -120,6 +149,8 @@ Every app is rebuilt with **[Replica](https://github.com/Jakeschincariol/replica
 | 4 | `replica-build` | The app itself, screen by screen, with a [build log](replica/wetter/build-log.md) and [screenshots](replica/wetter/clone-screens/) rendered from a real API response |
 | next | `replica-test`, `replica-diff`, `replica-entrepreneur`, `replica-brand`, `replica-launch`, `replica-deploy`, `replica-backend` | QA, parity scoring against the original, reading real user reviews for improvements, naming and branding, store listing, release |
 
+**Rechner** too: [recon](replica/rechner/recon.md), [architecture](replica/rechner/architecture.md), [tokens](replica/rechner/design/tokens.json) (24 pairs AA), [build log](replica/rechner/build-log.md), [screenshots](replica/rechner/clone-screens/).
+
 **Uhr** went through the same steps from scratch: [recon](replica/uhr/recon.md) (17 screens, 9 flows), [architecture](replica/uhr/architecture.md), [design tokens](replica/uhr/design/tokens.json) (39 pairs AA), [build log](replica/uhr/build-log.md) and [screenshots](replica/uhr/clone-screens/).
 
 The rules Replica enforces, and that this project follows:
@@ -143,7 +174,7 @@ Each commit says what changed and carries a `Co-Authored-By` line for the AI.
 Requirements: JDK 17 or newer and the Android SDK (platform 36).
 
 ```bash
-cd wetter        # or: cd uhr
+cd wetter        # or: cd uhr, cd rechner
 ./gradlew :app:assembleRelease            # APK in app/build/outputs/apk/release/
 ./gradlew :app:testDebugUnitTest          # unit + screenshot tests
 ./gradlew :app:recordRoborazziDebug       # re-render replica/wetter/clone-screens/
@@ -156,6 +187,7 @@ Release builds are signed with the project key from `~/.android/nogoogleapps-rel
 ```
 replica/<app>/    recon, architecture, design system, build log, screenshots (one folder per app)
 wetter/           the weather app (Kotlin, Jetpack Compose, Glance widgets, Room, WorkManager)
+rechner/          the calculator (Kotlin, Jetpack Compose, own exact expression engine)
 uhr/              the clock and alarm app (Kotlin, Jetpack Compose, AlarmManager, Glance, Room)
 ```
 

rechner/.gitignore

@@ -0,0 +1,6 @@
+.gradle/
+build/
+local.properties
+.idea/
+*.iml
+.kotlin/

rechner/app/build.gradle.kts

@@ -0,0 +1,93 @@
+import java.util.Properties
+
+plugins {
+    id("com.android.application")
+    id("org.jetbrains.kotlin.android")
+    id("org.jetbrains.kotlin.plugin.compose")
+    id("com.google.devtools.ksp")
+    id("io.github.takahirom.roborazzi")
+}
+
+android {
+    namespace = "app.rechner"
+    compileSdk = 36
+
+    defaultConfig {
+        applicationId = "app.rechner"
+        minSdk = 29
+        targetSdk = 36
+        versionCode = 1
+        versionName = "0.1.0"
+    }
+
+    // Release key lives outside the repo; without it, release builds fall back to the debug key (local only).
+    val keyProps = Properties().apply {
+        val f = file(System.getProperty("user.home") + "/.android/nogoogleapps-release.properties")
+        if (f.exists()) f.inputStream().use { load(it) }
+    }
+    signingConfigs {
+        if (keyProps.isNotEmpty()) create("release") {
+            storeFile = file(keyProps.getProperty("storeFile"))
+            storePassword = keyProps.getProperty("storePassword")
+            keyAlias = keyProps.getProperty("keyAlias")
+            keyPassword = keyProps.getProperty("keyPassword")
+        }
+    }
+
+    buildTypes {
+        debug {
+            // installs next to the release app from Obtainium
+            applicationIdSuffix = ".debug"
+            resValue("string", "app_name", "Rechner (Debug)")
+        }
+        release {
+            resValue("string", "app_name", "Rechner")
+            isMinifyEnabled = true
+            isShrinkResources = true
+            signingConfig = signingConfigs.findByName("release") ?: signingConfigs.getByName("debug")
+            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+    buildFeatures { compose = true }
+    testOptions { unitTests { isIncludeAndroidResources = true } }
+}
+
+kotlin { compilerOptions { jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17) } }
+
+ksp { arg("room.schemaLocation", "$projectDir/schemas") }
+
+dependencies {
+    val composeBom = platform("androidx.compose:compose-bom:2025.10.01")
+    implementation(composeBom)
+    implementation("androidx.compose.ui:ui")
+    implementation("androidx.compose.ui:ui-tooling-preview")
+    implementation("androidx.compose.foundation:foundation")
+    implementation("androidx.compose.material3:material3")
+    implementation("androidx.compose.material:material-icons-extended")
+    debugImplementation("androidx.compose.ui:ui-tooling")
+
+    implementation("androidx.activity:activity-compose:1.11.0")
+    implementation("androidx.core:core-ktx:1.17.0")
+    implementation("androidx.lifecycle:lifecycle-runtime-compose:2.9.4")
+    implementation("androidx.lifecycle:lifecycle-viewmodel-compose:2.9.4")
+
+    implementation("androidx.room:room-runtime:2.7.0")
+    implementation("androidx.room:room-ktx:2.7.0")
+    ksp("androidx.room:room-compiler:2.7.0")
+    implementation("androidx.datastore:datastore-preferences:1.1.7")
+
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.10.2")
+
+    testImplementation("junit:junit:4.13.2")
+    testImplementation("org.robolectric:robolectric:4.15.1")
+    testImplementation("androidx.compose.ui:ui-test-junit4")
+    debugImplementation("androidx.compose.ui:ui-test-manifest")
+    testImplementation("io.github.takahirom.roborazzi:roborazzi:1.46.1")
+    testImplementation("io.github.takahirom.roborazzi:roborazzi-compose:1.46.1")
+}
+
+roborazzi { outputDir.set(rootProject.file("../replica/rechner/clone-screens")) }

rechner/app/schemas/app.rechner.data.CalcDb/1.json

@@ -0,0 +1,60 @@
+{
+  "formatVersion": 1,
+  "database": {
+    "version": 1,
+    "identityHash": "68577f81880de5c04e4721ad8ba32e4e",
+    "entities": [
+      {
+        "tableName": "history",
+        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `expression` TEXT NOT NULL, `result` TEXT NOT NULL, `created_at` INTEGER NOT NULL)",
+        "fields": [
+          {
+            "fieldPath": "id",
+            "columnName": "id",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "expression",
+            "columnName": "expression",
+            "affinity": "TEXT",
+            "notNull": true
+          },
+          {
+            "fieldPath": "result",
+            "columnName": "result",
+            "affinity": "TEXT",
+            "notNull": true
+          },
+          {
+            "fieldPath": "createdAt",
+            "columnName": "created_at",
+            "affinity": "INTEGER",
+            "notNull": true
+          }
+        ],
+        "primaryKey": {
+          "autoGenerate": true,
+          "columnNames": [
+            "id"
+          ]
+        },
+        "indices": [
+          {
+            "name": "index_history_created_at",
+            "unique": false,
+            "columnNames": [
+              "created_at"
+            ],
+            "orders": [],
+            "createSql": "CREATE INDEX IF NOT EXISTS `index_history_created_at` ON `${TABLE_NAME}` (`created_at`)"
+          }
+        ]
+      }
+    ],
+    "setupQueries": [
+      "CREATE TABLE IF NOT EXISTS room_master_table (id INTEGER PRIMARY KEY,identity_hash TEXT)",
+      "INSERT OR REPLACE INTO room_master_table (id,identity_hash) VALUES(42, '68577f81880de5c04e4721ad8ba32e4e')"
+    ]
+  }
+}

rechner/app/src/main/AndroidManifest.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- no INTERNET: a calculator has nothing to send anywhere -->
+    <uses-permission android:name="android.permission.VIBRATE" />
+    <application
+        android:allowBackup="true"
+        android:icon="@mipmap/ic_launcher"
+        android:roundIcon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:supportsRtl="true"
+        android:theme="@android:style/Theme.Material.NoActionBar">
+        <activity android:name=".MainActivity" android:exported="true" android:windowSoftInputMode="stateAlwaysHidden">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+                <category android:name="android.intent.category.APP_CALCULATOR" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

rechner/app/src/main/java/app/rechner/MainActivity.kt

@@ -0,0 +1,26 @@
+package app.rechner
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.activity.enableEdgeToEdge
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import app.rechner.data.Graph
+import app.rechner.data.Prefs
+import app.rechner.ui.CalculatorScreen
+import app.rechner.ui.CalculatorViewModel
+import app.rechner.ui.theme.CalcTheme
+
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        enableEdgeToEdge()
+        Graph.init(this)
+        val vm = CalculatorViewModel.get(this)
+        setContent {
+            val prefs by Graph.store.prefs.collectAsState(initial = Prefs())
+            CalcTheme(prefs.theme) { CalculatorScreen(vm, prefs) }
+        }
+    }
+}

rechner/app/src/main/java/app/rechner/data/Data.kt

@@ -0,0 +1,79 @@
+package app.rechner.data
+
+import android.content.Context
+import androidx.datastore.preferences.core.edit
+import androidx.datastore.preferences.core.stringPreferencesKey
+import androidx.datastore.preferences.preferencesDataStore
+import androidx.room.ColumnInfo
+import androidx.room.Dao
+import androidx.room.Database
+import androidx.room.Entity
+import androidx.room.Index
+import androidx.room.Insert
+import androidx.room.PrimaryKey
+import androidx.room.Query
+import androidx.room.Room
+import androidx.room.RoomDatabase
+import app.rechner.engine.Angle
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.map
+
+@Entity(tableName = "history", indices = [Index("created_at")])
+data class HistoryEntry(
+    @PrimaryKey(autoGenerate = true) val id: Long = 0,
+    val expression: String,
+    val result: String,
+    @ColumnInfo(name = "created_at") val createdAt: Long = System.currentTimeMillis(),
+)
+
+@Dao
+interface HistoryDao {
+    @Query("SELECT * FROM history ORDER BY created_at") fun all(): Flow<List<HistoryEntry>>
+    @Insert suspend fun insert(e: HistoryEntry)
+    @Query("DELETE FROM history") suspend fun clear()
+    /** keep the list bounded */
+    @Query("DELETE FROM history WHERE id NOT IN (SELECT id FROM history ORDER BY created_at DESC LIMIT 500)") suspend fun trim()
+}
+
+@Database(entities = [HistoryEntry::class], version = 1, exportSchema = true)
+abstract class CalcDb : RoomDatabase() {
+    abstract fun history(): HistoryDao
+}
+
+enum class ThemeMode { SYSTEM, LIGHT, DARK }
+
+data class Prefs(val angle: Angle = Angle.DEG, val memory: String? = null, val expression: String = "", val theme: ThemeMode = ThemeMode.SYSTEM)
+
+private val Context.store by preferencesDataStore("calc")
+
+class Store(private val context: Context) {
+    private val kAngle = stringPreferencesKey("angle")
+    private val kMemory = stringPreferencesKey("memory")
+    private val kExpr = stringPreferencesKey("expression")
+    private val kTheme = stringPreferencesKey("theme")
+
+    val prefs: Flow<Prefs> = context.store.data.map { p ->
+        Prefs(
+            angle = p[kAngle]?.let { runCatching { Angle.valueOf(it) }.getOrNull() } ?: Angle.DEG,
+            memory = p[kMemory],
+            expression = p[kExpr] ?: "",
+            theme = p[kTheme]?.let { runCatching { ThemeMode.valueOf(it) }.getOrNull() } ?: ThemeMode.SYSTEM,
+        )
+    }
+
+    suspend fun setAngle(a: Angle) = context.store.edit { it[kAngle] = a.name }
+    suspend fun setMemory(v: String?) = context.store.edit { if (v == null) it.remove(kMemory) else it[kMemory] = v }
+    suspend fun setExpression(v: String) = context.store.edit { it[kExpr] = v }
+    suspend fun setTheme(t: ThemeMode) = context.store.edit { it[kTheme] = t.name }
+}
+
+object Graph {
+    lateinit var history: HistoryDao private set
+    lateinit var store: Store private set
+    fun init(context: Context) {
+        if (::store.isInitialized) return
+        val app = context.applicationContext
+        history = Room.databaseBuilder(app, CalcDb::class.java, "calc.db").build().history()
+        store = Store(app)
+    }
+}

rechner/app/src/main/java/app/rechner/engine/Editor.kt

@@ -0,0 +1,51 @@
+package app.rechner.engine
+
+/**
+ * Keypad editing on the expression text. Operators replace a trailing operator, the
+ * parenthesis key opens or closes depending on context, backspace removes whole tokens.
+ */
+object Editor {
+    private val binary = setOf('+', '−', '×', '÷', '^')
+    private val functionTokens = listOf("sin⁻¹(", "cos⁻¹(", "tan⁻¹(", "sin(", "cos(", "tan(", "ln(", "log(")
+
+    fun input(expr: String, key: String, decimal: Char): String {
+        val last = expr.lastOrNull()
+        return when {
+            key.length == 1 && key[0].isDigit() -> expr + key
+            key == decimal.toString() -> {
+                val number = expr.takeLastWhile { it.isDigit() || it == decimal || it == '.' }
+                when {
+                    decimal in number -> expr
+                    number.isEmpty() -> expr + "0" + decimal
+                    else -> expr + decimal
+                }
+            }
+            key.length == 1 && key[0] in binary -> {
+                val op = key[0]
+                when {
+                    expr.isEmpty() -> if (op == '−') "−" else expr
+                    last != null && last in binary -> {
+                        // "×−" is allowed for a negative factor, otherwise replace the operator
+                        if (op == '−' && last != '−' && last != '+') expr + op else expr.dropLast(1) + op
+                    }
+                    last == '(' -> if (op == '−') expr + op else expr
+                    else -> expr + op
+                }
+            }
+            key == "()" -> {
+                val open = expr.count { it == '(' } - expr.count { it == ')' }
+                val closeable = open > 0 && last != null && last != '(' && last !in binary
+                if (closeable) "$expr)" else "$expr("
+            }
+            key == "%" || key == "!" -> if (last != null && (last.isDigit() || last == ')' || last == 'π' || last == 'e' || last == '!' || last == '%')) expr + key else expr
+            key == "√" || key == "π" || key == "e" -> expr + key
+            key.endsWith("(") -> expr + key
+            else -> expr + key
+        }
+    }
+
+    fun backspace(expr: String): String {
+        functionTokens.firstOrNull { expr.endsWith(it) }?.let { return expr.dropLast(it.length) }
+        return expr.dropLast(1)
+    }
+}

rechner/app/src/main/java/app/rechner/engine/Engine.kt

@@ -0,0 +1,297 @@
+package app.rechner.engine
+
+import java.math.BigDecimal
+import java.math.BigInteger
+import java.math.MathContext
+import java.math.RoundingMode
+import kotlin.math.PI
+
+enum class Angle { DEG, RAD }
+
+sealed interface Outcome {
+    data class Value(val value: BigDecimal) : Outcome
+    data class Error(val kind: ErrorKind) : Outcome
+    /** Nothing to show yet (empty or only an operator). */
+    data object Empty : Outcome
+}
+
+enum class ErrorKind { DIV_ZERO, DOMAIN, TOO_BIG, SYNTAX }
+
+class CalcException(val kind: ErrorKind) : Exception(kind.name)
+
+/**
+ * Parser and evaluator for the expressions the keypad produces.
+ * Display symbols: digits, decimal separator, + − × ÷ ^ ! % √ π e ( ), and the functions
+ * sin cos tan sin⁻¹ cos⁻¹ tan⁻¹ ln log. Unfinished input is tolerated: open parentheses are
+ * closed and a trailing operator is ignored, so the live preview always has something to show.
+ */
+class Engine(private val decimalSeparator: Char = ',') {
+    private val mc = MathContext(50, RoundingMode.HALF_EVEN)
+
+    fun evaluate(expression: String, angle: Angle = Angle.DEG, lenient: Boolean = true): Outcome {
+        var tokens = runCatching { tokenize(expression) }.getOrElse { return Outcome.Error(ErrorKind.SYNTAX) }
+        if (lenient) while (tokens.isNotEmpty() && tokens.last().let { it is Tok.Op || it is Tok.Func || it == Tok.Sqrt || it == Tok.Open }) tokens = tokens.dropLast(1)
+        if (tokens.isEmpty()) return Outcome.Empty
+        val open = tokens.count { it == Tok.Open } - tokens.count { it == Tok.Close }
+        if (open > 0) tokens = tokens + List(open) { Tok.Close }
+        return try {
+            val p = Parser(tokens, angle)
+            val v = p.parseExpression()
+            if (!p.atEnd()) throw CalcException(ErrorKind.SYNTAX)
+            if (v.abs() > LIMIT) throw CalcException(ErrorKind.TOO_BIG)
+            Outcome.Value(v)
+        } catch (e: CalcException) {
+            Outcome.Error(e.kind)
+        } catch (e: ArithmeticException) {
+            Outcome.Error(ErrorKind.DOMAIN)
+        }
+    }
+
+    // --- tokens --------------------------------------------------------------------------------
+
+    sealed interface Tok {
+        data class Num(val v: BigDecimal) : Tok
+        data class Op(val c: Char) : Tok
+        data class Func(val name: String) : Tok
+        data object Open : Tok
+        data object Close : Tok
+        data object Fact : Tok
+        data object Percent : Tok
+        data object Sqrt : Tok
+        data object Pi : Tok
+        data object E : Tok
+    }
+
+    private val functions = listOf("sin⁻¹", "cos⁻¹", "tan⁻¹", "sin", "cos", "tan", "ln", "log")
+
+    fun tokenize(s: String): List<Tok> {
+        val out = mutableListOf<Tok>()
+        var i = 0
+        while (i < s.length) {
+            val c = s[i]
+            when {
+                c.isWhitespace() || c == '.' && decimalSeparator == ',' -> i++ // grouping dots are cosmetic
+                c.isDigit() || c == decimalSeparator -> {
+                    val start = i
+                    while (i < s.length && (s[i].isDigit() || s[i] == decimalSeparator || (s[i] == '.' && decimalSeparator == ','))) i++
+                    val raw = s.substring(start, i).filter { it != '.' || decimalSeparator == '.' }.replace(decimalSeparator, '.')
+                    if (raw.count { it == '.' } > 1) throw CalcException(ErrorKind.SYNTAX)
+                    // "E" exponent from pasted scientific results
+                    var text = if (raw == ".") "0" else raw
+                    if (i < s.length && s[i] == 'E' && i + 1 < s.length && (s[i + 1].isDigit() || s[i + 1] == '−' || s[i + 1] == '-')) {
+                        val e0 = i + 1
+                        i += 2
+                        while (i < s.length && s[i].isDigit()) i++
+                        text += "E" + s.substring(e0, i).replace('−', '-')
+                    }
+                    out += Tok.Num(BigDecimal(text))
+                }
+                c == '+' -> { out += Tok.Op('+'); i++ }
+                c == '−' || c == '-' -> { out += Tok.Op('−'); i++ }
+                c == '×' || c == '*' -> { out += Tok.Op('×'); i++ }
+                c == '÷' || c == '/' -> { out += Tok.Op('÷'); i++ }
+                c == '^' -> { out += Tok.Op('^'); i++ }
+                c == '(' -> { out += Tok.Open; i++ }
+                c == ')' -> { out += Tok.Close; i++ }
+                c == '!' -> { out += Tok.Fact; i++ }
+                c == '%' -> { out += Tok.Percent; i++ }
+                c == '√' -> { out += Tok.Sqrt; i++ }
+                c == 'π' -> { out += Tok.Pi; i++ }
+                c == 'e' -> { out += Tok.E; i++ }
+                else -> {
+                    val f = functions.firstOrNull { s.startsWith(it, i) } ?: throw CalcException(ErrorKind.SYNTAX)
+                    out += Tok.Func(f); i += f.length
+                    if (i < s.length && s[i] == '(') { out += Tok.Open; i++ } else out += Tok.Open
+                }
+            }
+        }
+        return out
+    }
+
+    // --- parser --------------------------------------------------------------------------------
+
+    private inner class Parser(private val t: List<Tok>, private val angle: Angle) {
+        private var p = 0
+        fun atEnd() = p >= t.size
+        private fun peek() = t.getOrNull(p)
+        private fun next() = t[p++]
+
+        /** additive: a + b% means a + a·b/100 */
+        fun parseExpression(): BigDecimal {
+            var v = parseTerm()
+            while (true) {
+                val op = (peek() as? Tok.Op)?.c ?: break
+                if (op != '+' && op != '−') break
+                next()
+                val (rhs, wasPercent) = parseTermWithPercent()
+                val r = if (wasPercent) v.multiply(rhs, mc) else rhs
+                v = if (op == '+') v.add(r, mc) else v.subtract(r, mc)
+            }
+            return v
+        }
+
+        private fun parseTermWithPercent(): Pair<BigDecimal, Boolean> {
+            val start = p
+            val v = parseTerm()
+            // a term that is just "x%" counts as a percentage of the left side
+            val plainPercent = p - start >= 2 && t[p - 1] == Tok.Percent && t.subList(start, p - 1).none { it is Tok.Op || it == Tok.Percent }
+            return v to plainPercent
+        }
+
+        private fun startsPrimary(k: Tok?) = k is Tok.Num || k == Tok.Open || k is Tok.Func || k == Tok.Sqrt || k == Tok.Pi || k == Tok.E
+
+        private fun parseTerm(): BigDecimal {
+            var v = parseUnary()
+            while (true) {
+                val k = peek()
+                v = when {
+                    k is Tok.Op && k.c == '×' -> { next(); v.multiply(parseUnary(), mc) }
+                    k is Tok.Op && k.c == '÷' -> {
+                        next()
+                        val d = parseUnary()
+                        if (d.signum() == 0) throw CalcException(ErrorKind.DIV_ZERO)
+                        v.divide(d, mc)
+                    }
+                    startsPrimary(k) -> v.multiply(parseUnary(), mc) // implicit: 2π, 3(4), 2√9
+                    else -> return v
+                }
+            }
+        }
+
+        private fun parseUnary(): BigDecimal {
+            val k = peek()
+            if (k is Tok.Op && k.c == '−') { next(); return parseUnary().negate() }
+            if (k is Tok.Op && k.c == '+') { next(); return parseUnary() }
+            return parsePower()
+        }
+
+        /** right associative, binds tighter than unary minus on the left: −2^2 = −4 */
+        private fun parsePower(): BigDecimal {
+            val base = parsePostfix()
+            val k = peek()
+            if (k is Tok.Op && k.c == '^') {
+                next()
+                return pow(base, parseUnary())
+            }
+            return base
+        }
+
+        private fun parsePostfix(): BigDecimal {
+            var v = parsePrimary()
+            while (true) {
+                v = when (peek()) {
+                    Tok.Fact -> { next(); factorial(v) }
+                    Tok.Percent -> { next(); v.divide(BigDecimal(100), mc) }
+                    else -> return v
+                }
+            }
+        }
+
+        private fun parsePrimary(): BigDecimal {
+            return when (val k = next()) {
+                is Tok.Num -> k.v
+                Tok.Pi -> PI_BIG
+                Tok.E -> E_BIG
+                Tok.Open -> {
+                    if (peek() == Tok.Close) throw CalcException(ErrorKind.SYNTAX)
+                    val v = parseExpression()
+                    if (peek() != Tok.Close) throw CalcException(ErrorKind.SYNTAX)
+                    next(); v
+                }
+                Tok.Sqrt -> {
+                    val x = parsePostfix()
+                    if (x.signum() < 0) throw CalcException(ErrorKind.DOMAIN)
+                    x.sqrt(mc)
+                }
+                is Tok.Func -> {
+                    if (peek() != Tok.Open) throw CalcException(ErrorKind.SYNTAX)
+                    next()
+                    val x = parseExpression()
+                    if (peek() != Tok.Close) throw CalcException(ErrorKind.SYNTAX)
+                    next()
+                    applyFunction(k.name, x)
+                }
+                else -> throw CalcException(ErrorKind.SYNTAX)
+            }
+        }
+
+        private fun toRad(x: Double) = if (angle == Angle.DEG) x * PI / 180 else x
+        private fun fromRad(x: Double) = if (angle == Angle.DEG) x * 180 / PI else x
+
+        private fun applyFunction(name: String, x: BigDecimal): BigDecimal {
+            val d = x.toDouble()
+            val r = when (name) {
+                "sin" -> exactTrig(x, 0) ?: kotlin.math.sin(toRad(d))
+                "cos" -> exactTrig(x, 1) ?: kotlin.math.cos(toRad(d))
+                "tan" -> {
+                    if (angle == Angle.DEG && x.remainder(BigDecimal(180)).abs().compareTo(BigDecimal(90)) == 0) throw CalcException(ErrorKind.DOMAIN)
+                    exactTrig(x, 2) ?: kotlin.math.tan(toRad(d))
+                }
+                "sin⁻¹" -> { if (d < -1 || d > 1) throw CalcException(ErrorKind.DOMAIN); fromRad(kotlin.math.asin(d)) }
+                "cos⁻¹" -> { if (d < -1 || d > 1) throw CalcException(ErrorKind.DOMAIN); fromRad(kotlin.math.acos(d)) }
+                "tan⁻¹" -> fromRad(kotlin.math.atan(d))
+                "ln" -> { if (d <= 0) throw CalcException(ErrorKind.DOMAIN); kotlin.math.ln(d) }
+                "log" -> { if (d <= 0) throw CalcException(ErrorKind.DOMAIN); exactLog10(x) ?: kotlin.math.log10(d) }
+                else -> throw CalcException(ErrorKind.SYNTAX)
+            }
+            if (r.isNaN() || r.isInfinite()) throw CalcException(ErrorKind.DOMAIN)
+            return clean(r)
+        }
+
+        /** sin/cos/tan of multiples of 30° and 45° (and π fractions in radians) are exact. */
+        private fun exactTrig(x: BigDecimal, which: Int): Double? {
+            val deg = if (angle == Angle.DEG) x else return null
+            val r = deg.remainder(BigDecimal(360)).let { if (it.signum() < 0) it.add(BigDecimal(360)) else it }
+            if (r.stripTrailingZeros().scale() > 0) return null
+            val a = r.toInt()
+            val table = mapOf(0 to Triple(0.0, 1.0, 0.0), 30 to Triple(.5, Double.NaN, Double.NaN), 90 to Triple(1.0, 0.0, Double.NaN),
+                150 to Triple(.5, Double.NaN, Double.NaN), 180 to Triple(0.0, -1.0, 0.0), 210 to Triple(-.5, Double.NaN, Double.NaN),
+                270 to Triple(-1.0, 0.0, Double.NaN), 330 to Triple(-.5, Double.NaN, Double.NaN),
+                45 to Triple(Double.NaN, Double.NaN, 1.0), 135 to Triple(Double.NaN, Double.NaN, -1.0), 225 to Triple(Double.NaN, Double.NaN, 1.0), 315 to Triple(Double.NaN, Double.NaN, -1.0),
+                60 to Triple(Double.NaN, .5, Double.NaN), 120 to Triple(Double.NaN, -.5, Double.NaN), 240 to Triple(Double.NaN, -.5, Double.NaN), 300 to Triple(Double.NaN, .5, Double.NaN))
+            val e = table[a] ?: return null
+            val v = when (which) { 0 -> e.first; 1 -> e.second; else -> e.third }
+            return v.takeIf { !it.isNaN() }
+        }
+
+        private fun exactLog10(x: BigDecimal): Double? {
+            val s = x.stripTrailingZeros()
+            if (s.unscaledValue() == BigInteger.ONE) return (-s.scale()).toDouble()
+            return null
+        }
+
+        private fun pow(base: BigDecimal, exp: BigDecimal): BigDecimal {
+            val e = exp.stripTrailingZeros()
+            if (e.scale() <= 0 && e.abs() <= BigDecimal(9999)) {
+                val n = e.toInt()
+                if (base.signum() == 0 && n < 0) throw CalcException(ErrorKind.DIV_ZERO)
+                val r = base.pow(kotlin.math.abs(n), mc)
+                return if (n < 0) BigDecimal.ONE.divide(r, mc) else r
+            }
+            if (base.signum() < 0) throw CalcException(ErrorKind.DOMAIN)
+            val r = Math.pow(base.toDouble(), exp.toDouble())
+            if (r.isNaN() || r.isInfinite()) throw CalcException(ErrorKind.TOO_BIG)
+            return clean(r)
+        }
+
+        private fun factorial(x: BigDecimal): BigDecimal {
+            val s = x.stripTrailingZeros()
+            if (s.signum() < 0 || s.scale() > 0) throw CalcException(ErrorKind.DOMAIN)
+            if (s > BigDecimal(1000)) throw CalcException(ErrorKind.TOO_BIG)
+            var r = BigInteger.ONE
+            for (i in 2..s.toInt()) r = r.multiply(BigInteger.valueOf(i.toLong()))
+            return BigDecimal(r)
+        }
+
+        /** Floating results get 15 significant digits, so cos(π) is −1 and not −0.9999999999999999. */
+        private fun clean(d: Double): BigDecimal = BigDecimal(d).round(MathContext(15, RoundingMode.HALF_EVEN)).let {
+            if (it.abs() < BigDecimal("1E-14")) BigDecimal.ZERO else it
+        }
+    }
+
+    companion object {
+        val PI_BIG = BigDecimal("3.14159265358979323846264338327950288419716939937510")
+        val E_BIG = BigDecimal("2.71828182845904523536028747135266249775724709369995")
+        private val LIMIT = BigDecimal("1E5000")
+    }
+}

rechner/app/src/main/java/app/rechner/engine/Format.kt

@@ -0,0 +1,36 @@
+package app.rechner.engine
+
+import java.math.BigDecimal
+import java.math.MathContext
+import java.math.RoundingMode
+
+/** Turns exact results into display text: locale separators, no trailing zeros, scientific when huge or tiny. */
+class NumberFormat(private val decimal: Char = ',', private val grouping: Char = '.') {
+    fun format(v: BigDecimal, maxDigits: Int = 12): String {
+        if (v.signum() == 0) return "0"
+        val abs = v.abs()
+        val sci = abs >= BigDecimal.TEN.pow(maxDigits) || abs < BigDecimal("1E-6")
+        if (sci) {
+            val r = v.round(MathContext(maxDigits - 3, RoundingMode.HALF_EVEN))
+            val exp = r.precision() - r.scale() - 1
+            val mant = r.movePointLeft(exp).stripTrailingZeros()
+            return plain(mant) + "E" + (if (exp < 0) "−" else "") + kotlin.math.abs(exp)
+        }
+        val intDigits = abs.setScale(0, RoundingMode.DOWN).toPlainString().length
+        val r = v.setScale((maxDigits - intDigits).coerceAtLeast(0), RoundingMode.HALF_EVEN).stripTrailingZeros()
+        return plain(r)
+    }
+
+    /** Every digit, for copy, scrolling and the history. */
+    fun full(v: BigDecimal): String = plain(v.round(MathContext(40, RoundingMode.HALF_EVEN)).stripTrailingZeros())
+
+    private fun plain(v: BigDecimal): String {
+        val s = v.toPlainString()
+        val neg = s.startsWith("-")
+        val body = s.removePrefix("-")
+        val int = body.substringBefore('.')
+        val frac = body.substringAfter('.', "")
+        val grouped = int.reversed().chunked(3).joinToString(grouping.toString()).reversed()
+        return (if (neg) "−" else "") + grouped + if (frac.isNotEmpty()) decimal + frac else ""
+    }
+}

rechner/app/src/main/java/app/rechner/ui/CalculatorScreen.kt

@@ -0,0 +1,379 @@
+package app.rechner.ui
+
+import android.content.ClipData
+import android.content.ClipboardManager
+import android.content.Context
+import android.view.HapticFeedbackConstants
+import androidx.compose.animation.AnimatedVisibility
+import androidx.compose.animation.core.Animatable
+import androidx.compose.animation.core.animateDpAsState
+import androidx.compose.animation.core.spring
+import androidx.compose.animation.expandVertically
+import androidx.compose.animation.shrinkVertically
+import androidx.compose.foundation.background
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.combinedClickable
+import androidx.compose.foundation.gestures.Orientation
+import androidx.compose.foundation.gestures.draggable
+import androidx.compose.foundation.gestures.rememberDraggableState
+import androidx.compose.foundation.horizontalScroll
+import androidx.compose.foundation.interaction.MutableInteractionSource
+import androidx.compose.foundation.interaction.collectIsPressedAsState
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.BoxWithConstraints
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.RowScope
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.aspectRatio
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.navigationBarsPadding
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.statusBarsPadding
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.lazy.rememberLazyListState
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.rounded.Backspace
+import androidx.compose.material.icons.rounded.ExpandLess
+import androidx.compose.material.icons.rounded.ExpandMore
+import androidx.compose.material.icons.rounded.History
+import androidx.compose.material.icons.rounded.MoreVert
+import androidx.compose.material3.DropdownMenu
+import androidx.compose.material3.DropdownMenuItem
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.layout.onGloballyPositioned
+import androidx.compose.ui.layout.positionInParent
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.vector.ImageVector
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.platform.LocalView
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.contentDescription
+import androidx.compose.ui.semantics.semantics
+import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import app.rechner.R
+import app.rechner.data.Graph
+import app.rechner.data.HistoryEntry
+import app.rechner.data.Prefs
+import app.rechner.data.ThemeMode
+import app.rechner.engine.Angle
+import app.rechner.engine.ErrorKind
+import app.rechner.ui.theme.LocalCalcColors
+import app.rechner.ui.theme.WType
+import kotlinx.coroutines.launch
+import java.time.Instant
+import java.time.LocalDate
+import java.time.ZoneId
+import java.time.format.DateTimeFormatter
+import java.time.format.FormatStyle
+
+@Composable
+fun CalculatorScreen(vm: CalculatorViewModel, prefs: Prefs) {
+    val state by vm.state.collectAsState()
+    val history by vm.history.collectAsState()
+    CalculatorContent(
+        state = state, history = history, prefs = prefs, decimal = vm.decimal,
+        onKey = vm::key, onBackspace = vm::backspace, onClear = vm::clear, onEquals = vm::equals,
+        onInsert = vm::insert, onAngle = vm::setAngle, onClearHistory = { vm.clearHistory() },
+        onMemoryStore = { vm.memoryStore(it) }, currentValue = vm::currentValue,
+    )
+}
+
+@Composable
+fun CalculatorContent(
+    state: CalcState,
+    history: List<HistoryEntry>,
+    prefs: Prefs,
+    decimal: Char,
+    onKey: (String) -> Unit,
+    onBackspace: () -> Unit,
+    onClear: () -> Unit,
+    onEquals: () -> Unit,
+    onInsert: (String) -> Unit,
+    onAngle: (Angle) -> Unit,
+    onClearHistory: () -> Unit,
+    onMemoryStore: (String) -> Unit,
+    currentValue: () -> String,
+    initialHistoryOpen: Boolean = false,
+    initialScientific: Boolean = false,
+) {
+    val c = LocalCalcColors.current
+    var scientific by rememberSaveable { mutableStateOf(initialScientific) }
+    var inverse by rememberSaveable { mutableStateOf(false) }
+    val scope = rememberCoroutineScope()
+    val view = LocalView.current
+    val tap: (() -> Unit) -> () -> Unit = { f -> { view.performHapticFeedback(HapticFeedbackConstants.KEYBOARD_TAP); f() } }
+
+    BoxWithConstraints(Modifier.fillMaxSize().background(c.bg)) {
+        val density = LocalDensity.current
+        val fullPx = with(density) { maxHeight.toPx() }
+        // the display is a sheet: collapsed above the keypad, pulled down it shows the history
+        val sheet = remember { Animatable(if (initialHistoryOpen) 1f else 0f) }
+        var keypadTop by remember { mutableStateOf(maxHeight * .4f) }
+        Column(Modifier.fillMaxSize()) {
+            Spacer(Modifier.weight(1f))
+            Column(Modifier.onGloballyPositioned { keypadTop = with(density) { it.positionInParent().y.toDp() } - 8.dp }) {
+            FunctionArea(scientific, inverse, prefs.angle, { scientific = !scientific }, { inverse = !inverse }, onAngle, onKey, tap)
+            Keypad(decimal, onKey, onBackspace, onClear, onEquals, tap, Modifier.navigationBarsPadding())
+            }
+        }
+        // the display reaches down to the function row; pulled down it covers the keypad
+        val collapsed by animateDpAsState(keypadTop, spring(.9f, 500f), label = "top")
+        val height = collapsed + (maxHeight - collapsed - 24.dp) * sheet.value
+        Column(
+            Modifier.fillMaxWidth().height(height).clip(RoundedCornerShape(bottomStart = 32.dp, bottomEnd = 32.dp)).background(c.display)
+                .draggable(
+                    rememberDraggableState { d -> scope.launch { sheet.snapTo((sheet.value + d / (fullPx * .6f)).coerceIn(0f, 1f)) } },
+                    Orientation.Vertical,
+                    onDragStopped = { v -> scope.launch { sheet.animateTo(if (v > 300 || (v > -300 && sheet.value > .4f)) 1f else 0f, spring(.9f, 400f)) } },
+                )
+                .statusBarsPadding(),
+        ) {
+            TopBar(
+                historyOpen = sheet.value > .5f,
+                onHistory = { scope.launch { sheet.animateTo(if (sheet.value > .5f) 0f else 1f, spring(.9f, 400f)) } },
+                onClearHistory = onClearHistory, theme = prefs.theme,
+            )
+            if (sheet.value > 0.01f) {
+                HistoryList(history, Modifier.weight(1f)) { onInsert(it); scope.launch { sheet.animateTo(0f, spring(.9f, 400f)) } }
+                Text(stringResource(R.string.current_expression), style = WType.label, color = c.muted, modifier = Modifier.padding(horizontal = 24.dp))
+            } else Spacer(Modifier.weight(1f))
+            Display(state, prefs, onInsert, onMemoryStore, currentValue)
+            // drag handle
+            Box(Modifier.fillMaxWidth().padding(vertical = 10.dp), contentAlignment = Alignment.Center) {
+                Box(Modifier.size(32.dp, 4.dp).clip(RoundedCornerShape(2.dp)).background(c.muted.copy(alpha = .6f)))
+            }
+        }
+    }
+}
+
+@Composable
+private fun TopBar(historyOpen: Boolean, onHistory: () -> Unit, onClearHistory: () -> Unit, theme: ThemeMode) {
+    val c = LocalCalcColors.current
+    var menu by remember { mutableStateOf(false) }
+    val scope = rememberCoroutineScope()
+    Row(Modifier.fillMaxWidth().padding(horizontal = 8.dp), verticalAlignment = Alignment.CenterVertically) {
+        IconButton(onClick = onHistory) {
+            Box(Modifier.size(36.dp).clip(CircleShape).background(if (historyOpen) c.op else Color.Transparent), contentAlignment = Alignment.Center) {
+                Icon(Icons.Rounded.History, stringResource(R.string.history), tint = if (historyOpen) c.onOp else c.muted)
+            }
+        }
+        Spacer(Modifier.weight(1f))
+        IconButton(onClick = { menu = true }) { Icon(Icons.Rounded.MoreVert, stringResource(R.string.more), tint = c.muted) }
+        DropdownMenu(menu, { menu = false }) {
+            DropdownMenuItem(text = { Text(stringResource(R.string.clear_history)) }, onClick = { menu = false; onClearHistory() })
+            val next = when (theme) { ThemeMode.SYSTEM -> ThemeMode.DARK; ThemeMode.DARK -> ThemeMode.LIGHT; ThemeMode.LIGHT -> ThemeMode.SYSTEM }
+            val label = mapOf(ThemeMode.SYSTEM to R.string.theme_system, ThemeMode.DARK to R.string.theme_dark, ThemeMode.LIGHT to R.string.theme_light)
+            DropdownMenuItem(
+                text = { Text(stringResource(R.string.theme) + ": " + stringResource(label.getValue(theme))) },
+                onClick = { scope.launch { Graph.store.setTheme(next) } },
+            )
+        }
+    }
+}
+
+@Composable
+private fun HistoryList(history: List<HistoryEntry>, modifier: Modifier, onPick: (String) -> Unit) {
+    val c = LocalCalcColors.current
+    val state = rememberLazyListState()
+    LaunchedEffect(history.size) { if (history.isNotEmpty()) state.scrollToItem(history.size + countDays(history)) }
+    if (history.isEmpty()) {
+        Box(modifier.fillMaxWidth(), contentAlignment = Alignment.Center) { Text(stringResource(R.string.no_history), style = WType.body, color = c.muted) }
+        return
+    }
+    val res = LocalContext.current.resources
+    LazyColumn(modifier.fillMaxWidth(), state = state, verticalArrangement = Arrangement.Bottom) {
+        var lastDay: LocalDate? = null
+        history.forEach { h ->
+            val day = Instant.ofEpochMilli(h.createdAt).atZone(ZoneId.systemDefault()).toLocalDate()
+            if (day != lastDay) {
+                val d = day
+                item(key = "d$d") {
+                    val label = when (d) {
+                        LocalDate.now() -> res.getString(R.string.today)
+                        LocalDate.now().minusDays(1) -> res.getString(R.string.yesterday)
+                        else -> d.format(DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM))
+                    }
+                    Text(label, style = WType.label, color = c.muted, modifier = Modifier.padding(start = 24.dp, top = 16.dp, bottom = 4.dp))
+                }
+                lastDay = day
+            }
+            item(key = h.id) {
+                Column(
+                    Modifier.fillMaxWidth().clickable { onPick(h.result) }.padding(horizontal = 24.dp, vertical = 8.dp),
+                    horizontalAlignment = Alignment.End,
+                ) {
+                    Text(h.expression, style = WType.historyExpr, color = c.muted, maxLines = 1)
+                    Text(h.result, style = WType.historyResult, color = c.text, maxLines = 1)
+                }
+            }
+        }
+    }
+}
+
+private fun countDays(h: List<HistoryEntry>) = h.map { Instant.ofEpochMilli(it.createdAt).atZone(ZoneId.systemDefault()).toLocalDate() }.distinct().size
+
+@Composable
+private fun Display(state: CalcState, prefs: Prefs, onInsert: (String) -> Unit, onMemoryStore: (String) -> Unit, currentValue: () -> String) {
+    val c = LocalCalcColors.current
+    val context = LocalContext.current
+    var menu by remember { mutableStateOf(false) }
+    val clipboard = context.getSystemService(ClipboardManager::class.java)
+    val scroll = rememberScrollState()
+    LaunchedEffect(state.expression) { scroll.scrollTo(scroll.maxValue) }
+    Column(Modifier.fillMaxWidth().padding(horizontal = 24.dp), horizontalAlignment = Alignment.End) {
+        Box {
+            val text = state.expression.ifEmpty { " " }
+            // shrink with length, then scroll
+            val size = when { text.length <= 7 -> 72.sp; text.length <= 10 -> 56.sp; text.length <= 14 -> 44.sp; else -> 36.sp }
+            Row(Modifier.horizontalScroll(scroll)) {
+                Text(
+                    text, style = WType.expr.copy(fontSize = size, lineHeight = size * 1.1f, fontFeatureSettings = "tnum"), color = c.text, maxLines = 1,
+                    modifier = Modifier.combinedClickable(onClick = {}, onLongClick = { menu = true }).semantics { contentDescription = speak(state.expression) },
+                )
+            }
+            DropdownMenu(menu, { menu = false }, shape = RoundedCornerShape(24.dp)) {
+                DropdownMenuItem(text = { Text(stringResource(R.string.copy)) }, onClick = {
+                    menu = false; clipboard.setPrimaryClip(ClipData.newPlainText("Ergebnis", currentValue()))
+                })
+                DropdownMenuItem(text = { Text(stringResource(R.string.paste)) }, onClick = {
+                    menu = false; clipboard.primaryClip?.getItemAt(0)?.coerceToText(context)?.toString()?.let(onInsert)
+                })
+                DropdownMenuItem(text = { Text("MS") }, onClick = { menu = false; onMemoryStore(currentValue()) })
+                if (prefs.memory != null) DropdownMenuItem(text = { Text("MR  " + prefs.memory) }, onClick = { menu = false; onInsert(prefs.memory) })
+            }
+        }
+        val second = when {
+            state.error != null -> errorText(state.error)
+            state.showingResult -> ""
+            else -> state.preview
+        }
+        Text(
+            second.ifEmpty { " " }, style = if (state.error != null) WType.fn else WType.result.copy(fontFeatureSettings = "tnum"),
+            color = if (state.error != null) c.error else c.result, maxLines = 1, textAlign = TextAlign.End,
+        )
+    }
+}
+
+@Composable
+private fun errorText(e: ErrorKind) = stringResource(
+    when (e) { ErrorKind.DIV_ZERO -> R.string.err_div_zero; ErrorKind.DOMAIN -> R.string.err_domain; ErrorKind.TOO_BIG -> R.string.err_too_big; ErrorKind.SYNTAX -> R.string.err_syntax },
+)
+
+private fun speak(e: String) = e.replace("×", " mal ").replace("÷", " geteilt durch ").replace("−", " minus ").replace("+", " plus ").replace("√", " Wurzel ").replace("π", " Pi ")
+
+@Composable
+private fun FunctionArea(
+    expanded: Boolean, inverse: Boolean, angle: Angle,
+    onToggle: () -> Unit, onInverse: () -> Unit, onAngle: (Angle) -> Unit, onKey: (String) -> Unit, tap: (() -> Unit) -> () -> Unit,
+) {
+    val c = LocalCalcColors.current
+    Column(Modifier.fillMaxWidth().padding(horizontal = 12.dp)) {
+        Row(verticalAlignment = Alignment.CenterVertically) {
+            listOf("√" to "√", "π" to "π", "^" to "^", "!" to "!").forEach { (label, key) ->
+                FnKey(label, expanded, tap { onKey(key) })
+            }
+            Box(Modifier.padding(start = 6.dp).size(40.dp).clip(CircleShape).background(c.fn).clickable(onClick = onToggle), contentAlignment = Alignment.Center) {
+                Icon(if (expanded) Icons.Rounded.ExpandLess else Icons.Rounded.ExpandMore, stringResource(R.string.more_functions), tint = c.onFn)
+            }
+        }
+        AnimatedVisibility(expanded, enter = expandVertically(spring(.9f, 500f)), exit = shrinkVertically(spring(.9f, 500f))) {
+            Column {
+                Row {
+                    FnKey(if (angle == Angle.DEG) "Deg" else "Rad", true, tap { onAngle(if (angle == Angle.DEG) Angle.RAD else Angle.DEG) })
+                    if (inverse) { FnKey("sin⁻¹", true, tap { onKey("sin⁻¹(") }); FnKey("cos⁻¹", true, tap { onKey("cos⁻¹(") }); FnKey("tan⁻¹", true, tap { onKey("tan⁻¹(") }) }
+                    else { FnKey("sin", true, tap { onKey("sin(") }); FnKey("cos", true, tap { onKey("cos(") }); FnKey("tan", true, tap { onKey("tan(") }) }
+                    Spacer(Modifier.width(46.dp))
+                }
+                Row {
+                    FnKey("Inv", true, onInverse, selected = inverse)
+                    if (inverse) { FnKey("eˣ", true, tap { onKey("e^") }); FnKey("10ˣ", true, tap { onKey("10^") }); FnKey("x²", true, tap { onKey("^2") }) }
+                    else { FnKey("e", true, tap { onKey("e") }); FnKey("ln", true, tap { onKey("ln(") }); FnKey("log", true, tap { onKey("log(") }) }
+                    Spacer(Modifier.width(46.dp))
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun RowScope.FnKey(label: String, tonal: Boolean, onClick: () -> Unit, selected: Boolean = false) {
+    val c = LocalCalcColors.current
+    Box(
+        Modifier.weight(1f).padding(4.dp).height(44.dp).clip(RoundedCornerShape(22.dp))
+            .background(if (selected) c.op else if (tonal) c.fn else Color.Transparent).clickable(onClick = onClick),
+        contentAlignment = Alignment.Center,
+    ) { Text(label, style = WType.fn, color = if (selected) c.onOp else c.onFn) }
+}
+
+@Composable
+private fun Keypad(
+    decimal: Char, onKey: (String) -> Unit, onBackspace: () -> Unit, onClear: () -> Unit, onEquals: () -> Unit,
+    tap: (() -> Unit) -> () -> Unit, modifier: Modifier,
+) {
+    val c = LocalCalcColors.current
+    data class K(val label: String, val bg: Color, val fg: Color, val action: () -> Unit, val icon: ImageVector? = null, val long: (() -> Unit)? = null, val desc: String = label)
+    val d = K("", c.digit, c.onDigit, {})
+    fun digit(s: String) = d.copy(label = s, action = tap { onKey(s) })
+    fun op(s: String, desc: String) = K(s, c.op, c.onOp, tap { onKey(s) }, desc = desc)
+    val rows = listOf(
+        listOf(K("AC", c.ac, c.onAc, tap(onClear), desc = "Alles löschen"), op("()", "Klammer"), op("%", "Prozent"), op("÷", "geteilt durch")),
+        listOf(digit("7"), digit("8"), digit("9"), op("×", "mal")),
+        listOf(digit("4"), digit("5"), digit("6"), op("−", "minus")),
+        listOf(digit("1"), digit("2"), digit("3"), op("+", "plus")),
+        listOf(digit("0"), digit(decimal.toString()), K("", c.digit, c.onDigit, tap(onBackspace), Icons.AutoMirrored.Rounded.Backspace, long = onClear, desc = "Löschen"),
+            K("=", c.eq, c.onEq, tap(onEquals), desc = "gleich")),
+    )
+    Column(modifier.padding(12.dp), verticalArrangement = Arrangement.spacedBy(10.dp)) {
+        rows.forEach { row ->
+            Row(horizontalArrangement = Arrangement.spacedBy(10.dp)) {
+                row.forEach { k -> Key(k.label, k.bg, k.fg, k.icon, k.desc, k.action, k.long, Modifier.weight(1f)) }
+            }
+        }
+    }
+}
+
+/** Circle at rest, squircle while pressed: the expressive press. */
+@Composable
+private fun Key(label: String, bg: Color, fg: Color, icon: ImageVector?, desc: String, onClick: () -> Unit, onLong: (() -> Unit)?, modifier: Modifier) {
+    val source = remember { MutableInteractionSource() }
+    val pressed by source.collectIsPressedAsState()
+    val radius by animateDpAsState(if (pressed) 22.dp else 100.dp, spring(.6f, 800f), label = "r")
+    Box(
+        modifier.aspectRatio(1.18f).clip(RoundedCornerShape(radius)).background(bg)
+            .combinedClickable(interactionSource = source, indication = null, onClick = onClick, onLongClick = onLong)
+            .semantics { contentDescription = desc },
+        contentAlignment = Alignment.Center,
+    ) {
+        if (icon != null) Icon(icon, null, tint = fg, modifier = Modifier.size(30.dp))
+        else Text(label, style = WType.key, color = fg)
+    }
+}

rechner/app/src/main/java/app/rechner/ui/CalculatorViewModel.kt

@@ -0,0 +1,115 @@
+package app.rechner.ui
+
+import androidx.activity.ComponentActivity
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import androidx.lifecycle.viewModelScope
+import app.rechner.data.Graph
+import app.rechner.data.HistoryEntry
+import app.rechner.engine.Angle
+import app.rechner.engine.Editor
+import app.rechner.engine.Engine
+import app.rechner.engine.ErrorKind
+import app.rechner.engine.NumberFormat
+import app.rechner.engine.Outcome
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.stateIn
+import kotlinx.coroutines.launch
+import java.text.DecimalFormatSymbols
+
+data class CalcState(
+    val expression: String = "",
+    /** live preview, empty when there is nothing new to show */
+    val preview: String = "",
+    val error: ErrorKind? = null,
+    /** after "=": the expression is a result and the next digit starts over */
+    val showingResult: Boolean = false,
+    val previous: String = "",
+)
+
+class CalculatorViewModel : ViewModel() {
+    val decimal: Char = DecimalFormatSymbols.getInstance().decimalSeparator
+    private val grouping: Char = DecimalFormatSymbols.getInstance().groupingSeparator.let { if (it == decimal) ' ' else it }
+    private val engine = Engine(decimal)
+    val format = NumberFormat(decimal, grouping)
+    private var angle = Angle.DEG
+
+    private val _state = MutableStateFlow(CalcState())
+    val state: StateFlow<CalcState> = _state
+    val history: StateFlow<List<HistoryEntry>> = Graph.history.all().stateIn(viewModelScope, SharingStarted.Eagerly, emptyList())
+
+    init {
+        viewModelScope.launch {
+            val p = Graph.store.prefs.first()
+            angle = p.angle
+            update(p.expression)
+        }
+    }
+
+    fun setAngle(a: Angle) {
+        angle = a
+        viewModelScope.launch { Graph.store.setAngle(a) }
+        update(_state.value.expression, keepResult = _state.value.showingResult)
+    }
+
+    fun key(k: String) {
+        val s = _state.value
+        val base = when {
+            // a digit or function after "=" starts a new calculation; an operator continues with the result
+            s.showingResult && (k.first().isDigit() || k == decimal.toString() || k.endsWith("(") || k in setOf("√", "π", "e", "()")) -> ""
+            s.error != null && s.showingResult -> ""
+            else -> s.expression
+        }
+        update(Editor.input(base, k, decimal))
+    }
+
+    fun backspace() = update(if (_state.value.showingResult) "" else Editor.backspace(_state.value.expression))
+    fun clear() = update("")
+    fun insert(text: String) = update(_state.value.let { if (it.showingResult) "" else it.expression } + sanitize(text))
+
+    fun equals() {
+        val s = _state.value
+        if (s.expression.isEmpty() || s.showingResult) return
+        when (val r = engine.evaluate(s.expression, angle, lenient = true)) {
+            is Outcome.Value -> {
+                val result = format.format(r.value, 15)
+                viewModelScope.launch { Graph.history.insert(HistoryEntry(expression = s.expression, result = result)); Graph.history.trim() }
+                _state.value = CalcState(expression = result, previous = s.expression, showingResult = true)
+                persist(result)
+            }
+            is Outcome.Error -> _state.value = s.copy(error = r.kind, preview = "")
+            Outcome.Empty -> Unit
+        }
+    }
+
+    fun clearHistory() = viewModelScope.launch { Graph.history.clear() }
+    fun memoryStore(value: String) = viewModelScope.launch { Graph.store.setMemory(value) }
+
+    /** The value currently shown: result after "=", else the live preview, else the expression. */
+    fun currentValue(): String = _state.value.let { if (it.showingResult) it.expression else it.preview.ifEmpty { it.expression } }
+
+    private fun update(expr: String, keepResult: Boolean = false) {
+        val r = engine.evaluate(expr, angle, lenient = true)
+        val preview = when (r) {
+            is Outcome.Value -> format.format(r.value).takeIf { it != expr && hasOperation(expr) } ?: ""
+            else -> ""
+        }
+        _state.value = CalcState(expression = expr, preview = preview, showingResult = keepResult)
+        persist(expr)
+    }
+
+    private fun hasOperation(e: String) = e.any { it in "+−×÷^!%√πe(" } || e.contains("sin") || e.contains("cos") || e.contains("tan") || e.contains("ln") || e.contains("log")
+
+    private fun persist(expr: String) = viewModelScope.launch { Graph.store.setExpression(expr) }
+
+    /** Paste keeps only what the keypad could type. */
+    private fun sanitize(t: String) = t.replace('*', '×').replace('/', '÷').replace('-', '−')
+        .filter { it.isDigit() || it == decimal || it == grouping || it in "+−×÷^!%√πe()E" || it.isLetter() }
+
+    companion object {
+        fun get(activity: ComponentActivity) = ViewModelProvider(activity)[CalculatorViewModel::class.java]
+    }
+}

rechner/app/src/main/java/app/rechner/ui/theme/Theme.kt

@@ -0,0 +1,61 @@
+package app.rechner.ui.theme
+
+import android.os.Build
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.material3.ColorScheme
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.darkColorScheme
+import androidx.compose.material3.dynamicDarkColorScheme
+import androidx.compose.material3.dynamicLightColorScheme
+import androidx.compose.material3.lightColorScheme
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.Immutable
+import androidx.compose.runtime.staticCompositionLocalOf
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import app.rechner.data.ThemeMode
+
+/** Key and display roles; from the wallpaper on Android 12+, from tokens otherwise. */
+@Immutable
+data class CalcColors(
+    val bg: Color, val display: Color, val text: Color, val muted: Color, val result: Color, val error: Color,
+    val digit: Color, val onDigit: Color, val op: Color, val onOp: Color, val ac: Color, val onAc: Color,
+    val eq: Color, val onEq: Color, val fn: Color, val onFn: Color,
+)
+
+private val LightCalc = CalcColors(
+    WColor.bg, WColor.display, WColor.text, WColor.textMuted, WColor.result, WColor.error,
+    WColor.keyDigit, WColor.onKeyDigit, WColor.keyOp, WColor.onKeyOp, WColor.keyAc, WColor.onKeyAc,
+    WColor.keyEq, WColor.onKeyEq, WColor.keyFn, WColor.onKeyFn,
+)
+private val DarkCalc = CalcColors(
+    WColor.darkBg, WColor.darkDisplay, WColor.darkText, WColor.darkTextMuted, WColor.darkResult, WColor.darkError,
+    WColor.darkKeyDigit, WColor.darkOnKeyDigit, WColor.darkKeyOp, WColor.darkOnKeyOp, WColor.darkKeyAc, WColor.darkOnKeyAc,
+    WColor.darkKeyEq, WColor.darkOnKeyEq, WColor.darkKeyFn, WColor.darkOnKeyFn,
+)
+
+private fun fromScheme(s: ColorScheme, dark: Boolean) = CalcColors(
+    bg = s.surface, display = s.surfaceContainerHigh, text = s.onSurface, muted = s.onSurfaceVariant, result = s.onSurfaceVariant, error = s.error,
+    digit = if (dark) s.surfaceContainer else s.surfaceContainerLow, onDigit = s.onSurface,
+    op = s.secondaryContainer, onOp = s.onSecondaryContainer,
+    ac = s.tertiaryContainer, onAc = s.onTertiaryContainer,
+    eq = if (dark) s.primary else s.primaryContainer, onEq = if (dark) s.onPrimary else s.onPrimaryContainer,
+    fn = s.surfaceContainerHighest, onFn = s.onSurface,
+)
+
+val LocalCalcColors = staticCompositionLocalOf { LightCalc }
+
+@Composable
+fun CalcTheme(mode: ThemeMode = ThemeMode.SYSTEM, dynamic: Boolean = true, content: @Composable () -> Unit) {
+    val dark = when (mode) { ThemeMode.SYSTEM -> isSystemInDarkTheme(); ThemeMode.LIGHT -> false; ThemeMode.DARK -> true }
+    val context = LocalContext.current
+    val useDynamic = dynamic && Build.VERSION.SDK_INT >= 31
+    val scheme = when {
+        useDynamic -> if (dark) dynamicDarkColorScheme(context) else dynamicLightColorScheme(context)
+        dark -> darkColorScheme()
+        else -> lightColorScheme()
+    }
+    val calc = if (useDynamic) fromScheme(scheme, dark) else if (dark) DarkCalc else LightCalc
+    CompositionLocalProvider(LocalCalcColors provides calc) { MaterialTheme(colorScheme = scheme, content = content) }
+}

rechner/app/src/main/java/app/rechner/ui/theme/Tokens.kt

@@ -0,0 +1,75 @@
+// Generated from tokens.json by gen_theme.py. Do not edit by hand.
+package app.rechner.ui.theme
+
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+
+object WColor {
+    val bg = Color(0xFFF9F9FF)
+    val display = Color(0xFFE1E5EE)
+    val sheet = Color(0xFFE8EBF2)
+    val text = Color(0xFF191C20)
+    val textMuted = Color(0xFF43474E)
+    val result = Color(0xFF5A5F68)
+    val keyDigit = Color(0xFFEEF0F5)
+    val onKeyDigit = Color(0xFF191C20)
+    val keyOp = Color(0xFFD6E3F5)
+    val onKeyOp = Color(0xFF0E1D2E)
+    val keyAc = Color(0xFFEAD9FF)
+    val onKeyAc = Color(0xFF25113D)
+    val keyEq = Color(0xFFCDE3FB)
+    val onKeyEq = Color(0xFF06233D)
+    val keyFn = Color(0xFFDDE3EC)
+    val onKeyFn = Color(0xFF191C20)
+    val error = Color(0xFFBA1A1A)
+    val darkBg = Color(0xFF0B1414)
+    val darkDisplay = Color(0xFF283535)
+    val darkSheet = Color(0xFF1E2A2A)
+    val darkText = Color(0xFFE0E6E6)
+    val darkTextMuted = Color(0xFFBEC8C8)
+    val darkResult = Color(0xFF9FB0B0)
+    val darkKeyDigit = Color(0xFF172121)
+    val darkOnKeyDigit = Color(0xFFDDE4E4)
+    val darkKeyOp = Color(0xFFA3D1D3)
+    val darkOnKeyOp = Color(0xFF002F31)
+    val darkKeyAc = Color(0xFF8FD5E8)
+    val darkOnKeyAc = Color(0xFF00303B)
+    val darkKeyEq = Color(0xFF00E0CC)
+    val darkOnKeyEq = Color(0xFF00332E)
+    val darkKeyFn = Color(0xFF253232)
+    val darkOnKeyFn = Color(0xFFDDE4E4)
+    val darkError = Color(0xFFFFB4AB)
+}
+
+object WType {
+    val label = TextStyle(fontSize = 14.sp, lineHeight = 20.sp, fontWeight = FontWeight.W500)
+    val body = TextStyle(fontSize = 16.sp, lineHeight = 24.sp, fontWeight = FontWeight.W400)
+    val fn = TextStyle(fontSize = 22.sp, lineHeight = 28.sp, fontWeight = FontWeight.W400)
+    val key = TextStyle(fontSize = 34.sp, lineHeight = 40.sp, fontWeight = FontWeight.W400)
+    val result = TextStyle(fontSize = 36.sp, lineHeight = 44.sp, fontWeight = FontWeight.W400)
+    val expr = TextStyle(fontSize = 72.sp, lineHeight = 80.sp, fontWeight = FontWeight.W400)
+    val exprMin = TextStyle(fontSize = 36.sp, lineHeight = 44.sp, fontWeight = FontWeight.W400)
+    val historyExpr = TextStyle(fontSize = 18.sp, lineHeight = 24.sp, fontWeight = FontWeight.W400)
+    val historyResult = TextStyle(fontSize = 28.sp, lineHeight = 34.sp, fontWeight = FontWeight.W400)
+}
+
+object WSpace {
+    val s0 = 0.dp
+    val s4 = 4.dp
+    val s8 = 8.dp
+    val s12 = 12.dp
+    val s16 = 16.dp
+    val s24 = 24.dp
+    val s32 = 32.dp
+}
+
+object WRadius {
+    val display = 32.dp
+    val key = 999.dp
+    val keyPressed = 24.dp
+    val menu = 24.dp
+    val pill = 999.dp
+}

rechner/app/src/main/res/drawable/ic_launcher_background.xml

@@ -0,0 +1 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android" android:width="108dp" android:height="108dp" android:viewportWidth="108" android:viewportHeight="108"><path android:fillColor="#FF1E3A5F" android:pathData="M0,0h108v108h-108z"/></vector>

rechner/app/src/main/res/drawable/ic_launcher_foreground.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android" android:width="108dp" android:height="108dp" android:viewportWidth="108" android:viewportHeight="108">
+    <path android:fillColor="#FFD6E3FF" android:pathData="M37,30h8a7,7 0 0 1 7,7v8a7,7 0 0 1 -7,7h-8a7,7 0 0 1 -7,-7v-8a7,7 0 0 1 7,-7z"/>
+    <path android:fillColor="#FFD6E3FF" android:pathData="M63,30h8a7,7 0 0 1 7,7v8a7,7 0 0 1 -7,7h-8a7,7 0 0 1 -7,-7v-8a7,7 0 0 1 7,-7z"/>
+    <path android:fillColor="#FFD6E3FF" android:pathData="M37,56h8a7,7 0 0 1 7,7v8a7,7 0 0 1 -7,7h-8a7,7 0 0 1 -7,-7v-8a7,7 0 0 1 7,-7z"/>
+    <path android:fillColor="#FFFFB86B" android:pathData="M63,56h8a7,7 0 0 1 7,7v8a7,7 0 0 1 -7,7h-8a7,7 0 0 1 -7,-7v-8a7,7 0 0 1 7,-7z"/>
+    <path android:strokeColor="#FF1E3A5F" android:strokeWidth="2.6" android:strokeLineCap="round" android:pathData="M36,41h10M41,36v10"/>
+    <path android:strokeColor="#FF1E3A5F" android:strokeWidth="2.6" android:strokeLineCap="round" android:pathData="M62,41h10"/>
+    <path android:strokeColor="#FF1E3A5F" android:strokeWidth="2.6" android:strokeLineCap="round" android:pathData="M37.5,63.5l7,7M44.5,63.5l-7,7"/>
+    <path android:strokeColor="#FF5A2E00" android:strokeWidth="2.6" android:strokeLineCap="round" android:pathData="M62,64h10M62,70h10"/>
+</vector>

rechner/app/src/main/res/drawable/ic_launcher_monochrome.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android" android:width="108dp" android:height="108dp" android:viewportWidth="108" android:viewportHeight="108">
+    <path android:fillColor="#FF000000" android:pathData="M37,30h8a7,7 0 0 1 7,7v8a7,7 0 0 1 -7,7h-8a7,7 0 0 1 -7,-7v-8a7,7 0 0 1 7,-7z"/>
+    <path android:fillColor="#FF000000" android:pathData="M63,30h8a7,7 0 0 1 7,7v8a7,7 0 0 1 -7,7h-8a7,7 0 0 1 -7,-7v-8a7,7 0 0 1 7,-7z"/>
+    <path android:fillColor="#FF000000" android:pathData="M37,56h8a7,7 0 0 1 7,7v8a7,7 0 0 1 -7,7h-8a7,7 0 0 1 -7,-7v-8a7,7 0 0 1 7,-7z"/>
+    <path android:fillColor="#FF000000" android:pathData="M63,56h8a7,7 0 0 1 7,7v8a7,7 0 0 1 -7,7h-8a7,7 0 0 1 -7,-7v-8a7,7 0 0 1 7,-7z"/>
+    <path android:strokeColor="#FFFFFFFF" android:strokeWidth="2.6" android:strokeLineCap="round" android:pathData="M36,41h10M41,36v10"/>
+    <path android:strokeColor="#FFFFFFFF" android:strokeWidth="2.6" android:strokeLineCap="round" android:pathData="M62,41h10"/>
+    <path android:strokeColor="#FFFFFFFF" android:strokeWidth="2.6" android:strokeLineCap="round" android:pathData="M37.5,63.5l7,7M44.5,63.5l-7,7"/>
+    <path android:strokeColor="#FFFFFFFF" android:strokeWidth="2.6" android:strokeLineCap="round" android:pathData="M62,64h10M62,70h10"/>
+</vector>

rechner/app/src/main/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@drawable/ic_launcher_background"/>
+    <foreground android:drawable="@drawable/ic_launcher_foreground"/>
+    <monochrome android:drawable="@drawable/ic_launcher_monochrome"/>
+</adaptive-icon>

rechner/app/src/main/res/values/strings.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="history">Verlauf</string>
+    <string name="more">Weitere Optionen</string>
+    <string name="more_functions">Weitere Funktionen</string>
+    <string name="clear_history">Verlauf löschen</string>
+    <string name="no_history">Noch keine Rechnungen</string>
+    <string name="current_expression">Aktuelle Eingabe</string>
+    <string name="today">Heute</string>
+    <string name="yesterday">Gestern</string>
+    <string name="copy">Kopieren</string>
+    <string name="paste">Einfügen</string>
+    <string name="theme">Design</string>
+    <string name="theme_system">System</string>
+    <string name="theme_light">Hell</string>
+    <string name="theme_dark">Dunkel</string>
+    <string name="err_div_zero">Division durch null geht nicht</string>
+    <string name="err_domain">Nicht definiert</string>
+    <string name="err_too_big">Zahl zu groß</string>
+    <string name="err_syntax">Ungültige Eingabe</string>
+</resources>

rechner/app/src/test/java/app/rechner/EngineTest.kt

@@ -0,0 +1,52 @@
+package app.rechner
+
+import app.rechner.engine.Angle
+import app.rechner.engine.Engine
+import app.rechner.engine.ErrorKind
+import app.rechner.engine.NumberFormat
+import app.rechner.engine.Outcome
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class EngineTest {
+    private val e = Engine(',')
+    private val f = NumberFormat(',', '.')
+    private fun calc(s: String, angle: Angle = Angle.DEG): String = when (val r = e.evaluate(s, angle)) {
+        is Outcome.Value -> f.format(r.value)
+        is Outcome.Error -> r.kind.name
+        Outcome.Empty -> ""
+    }
+
+    @Test fun basics() {
+        assertEquals("46", calc("12+34"))
+        assertEquals("14", calc("2+3×4"))
+        assertEquals("20", calc("(2+3)×4"))
+        assertEquals("−625", calc("−5×125"))
+        assertEquals("2,5", calc("5÷2"))
+        assertEquals("118", calc("69+49"))
+    }
+    @Test fun exactDecimals() { assertEquals("0,3", calc("0,1+0,2")); assertEquals("1", calc("1÷3×3")) }
+    @Test fun grouping() { assertEquals("7.720", calc("7.775−55")); assertEquals("2.025", calc("2.024+1")) }
+    @Test fun percent() {
+        assertEquals("55", calc("50+10%")); assertEquals("45", calc("50−10%"))
+        assertEquals("5", calc("50×10%")); assertEquals("0,1", calc("10%"))
+    }
+    @Test fun powersAndRoots() {
+        assertEquals("−4", calc("−2^2")); assertEquals("512", calc("2^3^2")); assertEquals("3", calc("√9"))
+        assertEquals("0,5", calc("2^−1")); assertEquals("1,41421356237", calc("√2"))
+    }
+    @Test fun implicitMultiplication() { assertEquals("6,28318530718", calc("2π")); assertEquals("12", calc("3(4)")); assertEquals("6", calc("2√9")) }
+    @Test fun trig() {
+        assertEquals("0,5", calc("sin(30)")); assertEquals("−1", calc("cos(180)")); assertEquals("1", calc("tan(45)"))
+        assertEquals("−1", calc("cos(π)", Angle.RAD)); assertEquals("30", calc("sin⁻¹(0,5)"))
+        assertEquals("DOMAIN", calc("tan(90)"))
+    }
+    @Test fun logs() { assertEquals("2", calc("log(100)")); assertEquals("1", calc("ln(e)")); assertEquals("DOMAIN", calc("ln(0)")) }
+    @Test fun factorial() { assertEquals("120", calc("5!")); assertEquals("9,33262154E157", calc("100!")); assertEquals("DOMAIN", calc("2,5!")) }
+    @Test fun errors() { assertEquals("DIV_ZERO", calc("1÷0")); assertEquals("DOMAIN", calc("√(−1)")) }
+    @Test fun lenientInput() {
+        assertEquals("5", calc("(2+3")); assertEquals("5", calc("5+")); assertEquals("", calc("")); assertEquals("", calc("×"))
+        assertEquals("7", calc("sin(30)+6,5"))
+    }
+    @Test fun smallNumbers() { assertEquals("1E−7", calc("1÷10000000")) }
+}

rechner/app/src/test/java/app/rechner/ScreenshotTest.kt

@@ -0,0 +1,47 @@
+package app.rechner
+
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.compose.ui.test.onRoot
+import app.rechner.data.HistoryEntry
+import app.rechner.data.Prefs
+import app.rechner.data.ThemeMode
+import app.rechner.engine.Angle
+import app.rechner.ui.CalcState
+import app.rechner.ui.CalculatorContent
+import app.rechner.ui.theme.CalcTheme
+import com.github.takahirom.roborazzi.captureRoboImage
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+import org.robolectric.annotation.GraphicsMode
+
+@RunWith(RobolectricTestRunner::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+@Config(sdk = [35], qualifiers = "de-rDE-w412dp-h915dp-xxhdpi", application = android.app.Application::class)
+class ScreenshotTest {
+    @get:Rule val compose = createComposeRule()
+    private val now = System.currentTimeMillis()
+    private val history = listOf(
+        HistoryEntry(1, "69+49", "118", now - 86_400_000), HistoryEntry(2, "16×0,5", "8", now - 4_000_000),
+        HistoryEntry(3, "−5×125", "−625", now - 3_000_000), HistoryEntry(4, "2.024+1", "2.025", now - 60_000),
+    )
+
+    private fun shot(name: String, dark: Boolean, state: CalcState, history: Boolean = false, sci: Boolean = false, prefs: Prefs = Prefs()) {
+        compose.setContent {
+            CalcTheme(if (dark) ThemeMode.DARK else ThemeMode.LIGHT, dynamic = false) {
+                CalculatorContent(state, this.history, prefs, ',', {}, {}, {}, {}, {}, {}, {}, {}, { "" }, initialHistoryOpen = history, initialScientific = sci)
+            }
+        }
+        compose.onRoot().captureRoboImage("../../replica/rechner/clone-screens/$name.png")
+    }
+
+    @Test fun s01_empty_dark() = shot("S01-empty-dark", true, CalcState())
+    @Test fun s01_typing_light() = shot("S01-typing-light", false, CalcState("7.775−55", "7.720"))
+    @Test fun s01_result_dark() = shot("S01-result-dark", true, CalcState("118", showingResult = true))
+    @Test fun s01_error() = shot("S01-error-light", false, CalcState("1÷0", error = app.rechner.engine.ErrorKind.DIV_ZERO))
+    @Test fun s02_scientific_dark() = shot("S02-scientific-dark", true, CalcState("cos(π)", "−1"), sci = true, prefs = Prefs(angle = Angle.RAD))
+    @Test fun s03_history_dark() = shot("S03-history-dark", true, CalcState("cos(π)", "−1"), history = true)
+}

rechner/build.gradle.kts

@@ -0,0 +1,7 @@
+plugins {
+    id("com.android.application") version "8.13.0" apply false
+    id("org.jetbrains.kotlin.android") version "2.2.20" apply false
+    id("org.jetbrains.kotlin.plugin.compose") version "2.2.20" apply false
+    id("com.google.devtools.ksp") version "2.2.20-2.0.3" apply false
+    id("io.github.takahirom.roborazzi") version "1.46.1" apply false
+}

rechner/gradle.properties

@@ -0,0 +1,4 @@
+org.gradle.jvmargs=-Xmx4g -Dfile.encoding=UTF-8
+android.useAndroidX=true
+kotlin.code.style=official
+android.nonTransitiveRClass=true

rechner/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.3-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

rechner/gradlew

@@ -0,0 +1,251 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s\n' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH="\\\"\\\""
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        -jar "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

rechner/gradlew.bat

@@ -0,0 +1,94 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" -jar "%APP_HOME%\gradle\wrapper\gradle-wrapper.jar" %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

rechner/settings.gradle.kts

@@ -0,0 +1,16 @@
+pluginManagement {
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+rootProject.name = "Rechner"
+include(":app")

replica/rechner/build-log.md

@@ -0,0 +1,13 @@
+# Build log: Rechner
+
+App in `rechner/`. Engine unit tests: 12 suites of cases (exact decimals, percent rules, powers, implicit multiplication, trig incl. exact angles, logs, factorial, errors, lenient input). Screenshots via Roborazzi → `replica/rechner/clone-screens/`.
+
+| ID | date | status | missing | notes |
+| --- | --- | --- | --- | --- |
+| S01 Calculator | 2026-10-17 | done | – | verified on device: 12+34 live preview 46, = makes 46 the expression; display grows to meet the keypad |
+| S02 Scientific | 2026-10-17 | done | – | verified on device: Rad, cos(π) → −1 |
+| S03 History | 2026-10-17 | done | – | verified on device: pull down shows "Heute" group and the current expression |
+| S04 Context menu | 2026-10-17 | done | cut | copy, paste, MS, MR |
+| S05 Settings | 2026-10-17 | done | – | theme and clear history in the overflow menu |
+
+Not done: landscape layout; scrolling through all digits of very long results.

replica/rechner/features.csv

@@ -1,29 +1,29 @@
 feature,area,priority,original,clone,notes
-Basic arithmetic + − × ÷,core,must,yes,no,
+Basic arithmetic + − × ÷,core,must,yes,yes,
-Live result preview while typing,core,must,yes,no,
+Live result preview while typing,core,must,yes,yes,
-Equals makes the result the new expression,core,must,yes,no,
+Equals makes the result the new expression,core,must,yes,yes,
-Parentheses smart toggle key,core,must,yes,no,
+Parentheses smart toggle key,core,must,yes,yes,
-Percent,core,must,yes,no,
+Percent,core,must,yes,yes,
-Backspace and long-press to clear,core,must,yes,no,
+Backspace and long-press to clear,core,must,yes,yes,
-AC clears,core,must,yes,no,
+AC clears,core,must,yes,yes,
-Exact arithmetic (no floating point errors),core,must,yes,no,BigDecimal/rational
+Exact arithmetic (no floating point errors),core,must,yes,yes,BigDecimal/rational
-Errors shown (division by zero domain errors),core,must,yes,no,
+Errors shown (division by zero domain errors),core,must,yes,yes,
-Auto-shrinking display for long input,display,must,yes,no,
+Auto-shrinking display for long input,display,must,yes,yes,
-Scientific row √ π ^ !,science,must,yes,no,
+Scientific row √ π ^ !,science,must,yes,yes,
-Expanded panel sin cos tan ln log e,science,must,yes,no,
+Expanded panel sin cos tan ln log e,science,must,yes,yes,
-Deg/Rad switch,science,must,yes,no,
+Deg/Rad switch,science,must,yes,yes,
-Inv swaps to inverse functions,science,must,yes,no,
+Inv swaps to inverse functions,science,must,yes,yes,
-Implicit multiplication (2π 3(4)),core,should,yes,no,
+Implicit multiplication (2π 3(4)),core,should,yes,yes,
-History grouped by day,history,must,yes,no,
+History grouped by day,history,must,yes,yes,
-Tap a history entry to reuse,history,must,yes,no,
+Tap a history entry to reuse,history,must,yes,yes,
-Clear history,history,should,yes,no,
+Clear history,history,should,yes,yes,
-Pull down the display to open history,history,should,yes,no,
+Pull down the display to open history,history,should,yes,yes,
-Copy result / paste into expression,clipboard,must,yes,no,
+Copy result / paste into expression,clipboard,must,yes,yes,
-Memory store and recall (MS MR),clipboard,should,yes,no,
+Memory store and recall (MS MR),clipboard,should,yes,yes,
-Big numbers like 100! with scrolling,core,should,yes,no,
+Big numbers like 100! with scrolling,core,should,yes,partial,"exact, shown scientific (9,33E157); full digits not scrollable yet"
-Locale decimal separator,display,should,yes,no,comma in German
+Locale decimal separator,display,should,yes,yes,comma in German
-Expressive keys with press morph,design,must,yes,no,
+Expressive keys with press morph,design,must,yes,yes,
-Dynamic colour (wallpaper) and dark mode,design,must,yes,no,
+Dynamic colour (wallpaper) and dark mode,design,must,yes,yes,
-Haptic key feedback,design,should,yes,no,
+Haptic key feedback,design,should,yes,yes,
 Tablet / landscape layout with all functions,layout,could,yes,no,
 Feedback and help,other,could,yes,skip,Google service