Long road starts here

library/build.gradle.kts

@@ -0,0 +1,101 @@
+import com.vanniktech.maven.publish.SonatypeHost
+import org.jetbrains.kotlin.gradle.ExperimentalKotlinGradlePluginApi
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
+plugins {
+    alias(libs.plugins.kotlinMultiplatform)
+    alias(libs.plugins.androidLibrary)
+    alias(libs.plugins.vanniktech.mavenPublish)
+    kotlin("plugin.serialization") version "2.1.20"
+}
+
+group = "net.sergeych"
+version = "0.0.1-SNAPSHOT"
+
+kotlin {
+    jvm()
+    androidTarget {
+        publishLibraryVariants("release")
+        @OptIn(ExperimentalKotlinGradlePluginApi::class)
+        compilerOptions {
+            jvmTarget.set(JvmTarget.JVM_11)
+        }
+    }
+//    iosX64()
+//    iosArm64()
+//    iosSimulatorArm64()
+    linuxX64()
+    js(IR) {
+        browser()
+        nodejs()
+    }
+
+    sourceSets {
+        all {
+            languageSettings.optIn("kotlinx.coroutines.ExperimentalCoroutinesApi")
+            languageSettings.optIn("kotlin.ExperimentalUnsignedTypes")
+            languageSettings.optIn("kotlin.coroutines.DelicateCoroutinesApi")
+        }
+
+        val commonMain by getting {
+            dependencies {
+                implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.8.1")
+                //put your multiplatform dependencies here
+                implementation(libs.kotlinx.coroutines.core)
+                implementation(libs.mp.bintools)
+            }
+        }
+        val commonTest by getting {
+            dependencies {
+                implementation(libs.kotlin.test)
+                implementation(libs.kotlinx.coroutines.test)
+            }
+        }
+    }
+}
+
+android {
+    namespace = "org.jetbrains.kotlinx.multiplatform.library.template"
+    compileSdk = libs.versions.android.compileSdk.get().toInt()
+    defaultConfig {
+        minSdk = libs.versions.android.minSdk.get().toInt()
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_11
+        targetCompatibility = JavaVersion.VERSION_11
+    }
+}
+
+mavenPublishing {
+    publishToMavenCentral(SonatypeHost.CENTRAL_PORTAL)
+
+    signAllPublications()
+
+    coordinates(group.toString(), "library", version.toString())
+
+    pom {
+        name = "Ling language"
+        description = "Kotlin-bound scripting loanguage"
+        inceptionYear = "2025"
+//        url = "https://sergeych.net"
+        licenses {
+            license {
+                name = "XXX"
+                url = "YYY"
+                distribution = "ZZZ"
+            }
+        }
+        developers {
+            developer {
+                id = "XXX"
+                name = "YYY"
+                url = "ZZZ"
+            }
+        }
+        scm {
+            url = "XXX"
+            connection = "YYY"
+            developerConnection = "ZZZ"
+        }
+    }
+}

library/src/commonMain/kotlin/net/sergeych/ling/Arguments.kt

@@ -0,0 +1,12 @@
+package net.sergeych.ling
+
+data class Arguments(val list: List<Statement> ) {
+
+    val size by list::size
+
+    operator fun get(index: Int): Statement = list[index]
+
+    companion object {
+        val EMPTY = Arguments(emptyList())
+    }
+}

library/src/commonMain/kotlin/net/sergeych/ling/Compiler.kt

@@ -0,0 +1,264 @@
+package net.sergeych.ling
+
+import kotlin.math.pow
+
+sealed class ObjType(name: String, val defaultValue: Obj? = null) {
+
+    class Str : ObjType("string", ObjString(""))
+    class Int : ObjType("real", ObjReal(0.0))
+
+}
+
+/**
+ * Descriptor for whatever object could be used as argument, return value,
+ * field, etc.
+ */
+data class ObjDescriptor(
+    val type: ObjType,
+    val mutable: Boolean,
+)
+
+data class MethodDescriptor(
+    val args: Array<ObjDescriptor>,
+    val result: ObjDescriptor
+)
+
+/*
+Meta context contains map of symbols.
+
+Each symbol can be:
+
+- a var
+- a const
+- a function
+- a type alias
+- a class definition
+
+Each have in common only its name.
+
+Var has: type, value. Const is same as var but value is fixed. Function has args and return value,
+type alias has target type name. So we have to have something that denotes a _type_
+
+ */
+
+
+//data class MetaContext(val symbols: MutableMap<String, > = mutableMapOf()) {
+//
+//}
+
+
+class Compiler {
+
+    fun compile(source: Source): Script {
+        val tokens = parseLing(source).listIterator()
+        val start = source.startPos
+        // at this level: "global" context: just script to execute or new function
+        // declaration forming closures
+        val statements = mutableListOf<Statement>()
+        while (parseStatement(tokens)?.also {
+                statements += it
+            } != null) {/**/
+        }
+        return Script(start, statements)
+    }
+
+    private fun parseStatement(tokens: ListIterator<Token>): Statement? {
+        val t = tokens.next()
+        return when (t.type) {
+            Token.Type.ID -> {
+                // could be keyword, assignment or just the expression
+                val next = tokens.next()
+                if (next.type == Token.Type.EQ) {
+                    // this _is_ assignment statement
+                    AssignStatement(
+                        t.pos, t.value,
+                        parseExpression(tokens) ?: throw ScriptError(
+                            t.pos,
+                            "Expecting expression for assignment operator"
+                        )
+                    )
+                }
+                // not assignment, maybe keyword statement:
+                // get back the token which is not '=':
+                tokens.previous()
+                // try keyword statement
+                parseKeywordStatement(t, tokens)
+                    ?: run {
+                        parseExpression(tokens)
+                    }
+            }
+
+            Token.Type.EOF -> null
+
+            else -> {
+                // could be expression
+                tokens.previous()
+                parseExpression(tokens)
+            }
+        }
+    }
+
+    private fun parseExpression(tokens: ListIterator<Token>, level: Int = 0): Statement? {
+        if (level == lastLevel)
+            return parseTerm(tokens)
+        var lvalue = parseExpression(tokens, level + 1)
+        if (lvalue == null) return null
+
+        while (true) {
+
+            val opToken = tokens.next()
+            val op = byLevel[level][opToken.value]
+            if (op == null) {
+                tokens.previous()
+                break
+            }
+
+            val rvalue = parseExpression(tokens, level + 1)
+                ?: throw ScriptError(opToken.pos, "Expecting expression")
+
+            lvalue = op.generate(opToken.pos, lvalue!!, rvalue)
+        }
+        return lvalue
+    }
+
+    fun parseTerm(tokens: ListIterator<Token>): Statement? {
+        // call op
+        // index op
+        // unary op
+        // parenthesis
+        // number or string
+        val t = tokens.next()
+        // todoL var?
+        return when (t.type) {
+//            "+" -> statement { parseNumber(true,tokens) }??????
+//            "-" -> statement { parseNumber(false,tokens) }
+//            "~" -> statement(t.pos) { ObjInt( parseLong(tokens)) }
+
+            Token.Type.PLUS -> {
+                val n = parseNumber(true, tokens)
+                statement(t.pos) { n }
+            }
+
+            Token.Type.MINUS -> {
+                val n = parseNumber(false, tokens)
+                statement(t.pos) { n }
+            }
+
+            Token.Type.INT, Token.Type.REAL, Token.Type.HEX -> {
+                tokens.previous()
+                val n = parseNumber(true, tokens)
+                statement(t.pos) { n }
+            }
+
+            else -> null
+        }
+
+    }
+
+
+    fun parseLong(tokens: ListIterator<Token>): Long =
+        // todo: hex notation?
+        getLong(tokens)
+
+    fun getLong(tokens: ListIterator<Token>): Long {
+        val t = tokens.next()
+        if (t.type != Token.Type.INT) throw ScriptError(t.pos, "expected number here")
+        return t.value.toLong()
+    }
+
+    fun parseNumber(isPlus: Boolean, tokens: ListIterator<Token>): Obj {
+        val t = tokens.next()
+        return when (t.type) {
+            Token.Type.INT, Token.Type.HEX -> {
+                val n = t.value.toLong(if (t.type == Token.Type.HEX) 16 else 10)
+                if (isPlus) ObjInt(n) else ObjInt(-n)
+            }
+
+            Token.Type.REAL -> {
+                val d = t.value.toDouble()
+                if (isPlus) ObjReal(d) else ObjReal(-d)
+            }
+
+            else -> {
+                throw ScriptError(t.pos, "expected number")
+            }
+        }
+    }
+
+    /**
+     * Parse keyword-starting statenment.
+     * @return parsed statement or null if, for example. [id] is not among keywords
+     */
+    private fun parseKeywordStatement(id: Token, tokens: ListIterator<Token>): Statement? {
+        return null
+    }
+
+//    fun parseStatement(parser: Parser): Statement? =
+//        parser.withToken {
+//            if (tokens.isEmpty()) null
+//            else {
+//                when (val token = tokens[0]) {
+//                    else -> {
+//                        rollback()
+//                        null
+//                    }
+//                }
+//            }
+//        }
+
+    companion object {
+        data class Operator(
+            val name: String,
+            val priority: Int, val arity: Int,
+            val generate: (Pos, Statement, Statement) -> Statement
+        )
+
+        val allOps = listOf(
+//            Operator("||", 0, 2) { pos, a, b -> LogicalOrStatement(pos, a, b) })
+            Operator("&&", 1, 2) { pos, a, b ->
+                LogicalAndStatement(pos, a, b)
+            },
+            // bitwise or 2
+            // bitwise and 3
+            // equality/ne 4
+            // relational <=,... 5
+            // shuttle <=> 6
+            // bitshhifts 7
+            // + - : 7
+            Operator("+", 7, 2) { pos, a, b ->
+                PlusStatement(pos, a, b)
+            },
+            Operator("-", 7, 2) { pos, a, b ->
+                MinusStatement(pos, a, b)
+            },
+            // * / %: 8
+        )
+        val lastLevel = 9
+        val byLevel: List<Map<String, Operator>> = (0..<lastLevel).map { l ->
+            allOps.filter { it.priority == l }
+                .map { it.name to it }.toMap()
+        }
+
+        fun compile(code: String): Script = Compiler().compile(Source("<eval>", code))
+    }
+}
+
+fun buildDoubleFromParts(
+    integerPart: Long,
+    decimalPart: Long,
+    exponent: Int
+): Double {
+    // Handle zero decimal case efficiently
+    val numDecimalDigits = if (decimalPart == 0L) 0 else decimalPart.toString().length
+
+    // Calculate decimal multiplier (10^-digits)
+    val decimalMultiplier = 10.0.pow(-numDecimalDigits)
+
+    // Combine integer and decimal parts
+    val baseValue = integerPart.toDouble() + decimalPart.toDouble() * decimalMultiplier
+
+    // Apply exponent
+    return baseValue * 10.0.pow(exponent)
+}
+
+suspend fun eval(code: String) = Compiler.compile(code).execute()

library/src/commonMain/kotlin/net/sergeych/ling/Context.kt

@@ -0,0 +1,46 @@
+package net.sergeych.ling
+
+import kotlin.math.PI
+
+class Context(
+    val callerPos: Pos,
+    val parent: Context? = null,
+    val args: Arguments = Arguments.EMPTY
+) {
+
+    data class Item(
+        val name: String, var value: Obj?,
+        val isMutable: Boolean = false
+    )
+
+    private val objects = mutableMapOf<String, Item>()
+
+    operator fun get(name: String): Item? = objects[name] ?: parent?.get(name)
+
+    fun copy(from: Pos, args: Arguments = Arguments.EMPTY): Context = Context(from, this, args)
+
+    fun addFn(name: String, fn: suspend Context.() -> Obj) = objects.put(name, Item(name,
+        object : Statement() {
+            override val pos: Pos = Pos.builtIn
+
+            override suspend fun execute(context: Context): Obj {
+                return try {
+                    context.fn()
+                } catch (e: Exception) {
+                    raise(e.message ?: "unexpected error")
+                }
+            }
+
+        })
+    )
+
+}
+
+val basicContext = Context(Pos.builtIn).apply {
+    addFn("println") {
+        require(args.size == 1)
+        println(args[0].execute(this).asStr.value)
+        Void
+    }
+    addFn("π") { ObjReal(PI) }
+}

library/src/commonMain/kotlin/net/sergeych/ling/Obj.kt

@@ -0,0 +1,59 @@
+package net.sergeych.ling
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlin.math.floor
+
+@Serializable
+sealed class Obj {
+    open val asStr: ObjString by lazy {
+        if( this is ObjString) this else ObjString(this.toString())
+    }
+}
+
+@Serializable
+@SerialName("void")
+object Void: Obj() {
+    override fun equals(other: Any?): Boolean {
+        return other is Void || other is Unit
+    }
+}
+
+@Serializable
+@SerialName("string")
+data class ObjString(val value: String): Obj() {
+    override fun toString(): String = value
+}
+
+interface Numeric {
+    val longValue: Long
+    val doubleValue: Double
+    val toObjInt: ObjInt
+    val toObjReal: ObjReal
+}
+
+@Serializable
+@SerialName("real")
+data class ObjReal(val value: Double): Obj(), Numeric {
+    override val asStr by lazy { ObjString(value.toString()) }
+    override val longValue: Long by lazy { floor(value).toLong() }
+    override val doubleValue: Double by lazy { value }
+    override val toObjInt: ObjInt by lazy { ObjInt(longValue) }
+    override val toObjReal: ObjReal by lazy { ObjReal(value) }
+}
+
+@Serializable
+@SerialName("int")
+data class ObjInt(val value: Long): Obj(), Numeric {
+    override val asStr by lazy { ObjString(value.toString()) }
+    override val longValue: Long by lazy { value }
+    override val doubleValue: Double by lazy { value.toDouble() }
+    override val toObjInt: ObjInt by lazy { ObjInt(value) }
+    override val toObjReal: ObjReal by lazy { ObjReal(doubleValue) }
+}
+
+@Serializable
+@SerialName("bool")
+data class ObjBool(val value: Boolean): Obj() {
+    override val asStr by lazy { ObjString(value.toString()) }
+}

library/src/commonMain/kotlin/net/sergeych/ling/Parser.kt

@@ -0,0 +1,184 @@
+package net.sergeych.ling
+
+private val idFirstChars: Set<Char> = (
+        ('a'..'z') + ('A'..'Z') + '_' + ('а'..'я') + ('А'..'Я')
+        ).toSet()
+val idNextChars: Set<Char> = idFirstChars + ('0'..'9')
+val digits = ('0'..'9').toSet()
+val hexDigits = digits + ('a'..'f') + ('A'..'F')
+
+fun parseLing(source: Source): List<Token> {
+    val p = Parser(fromPos = source.startPos)
+    val tokens = mutableListOf<Token>()
+    do {
+        val t = p.nextToken()
+        tokens += t
+    } while(t.type != Token.Type.EOF)
+    return tokens
+}
+
+private class Parser(fromPos: Pos) {
+
+    private val pos = MutablePos(fromPos)
+
+    /**
+     * Immutable copy of current position
+     */
+    private val currentPos: Pos get() = pos.toPos()
+
+    private fun raise(msg: String): Nothing = throw ScriptError(currentPos, msg)
+
+    fun nextToken(): Token {
+        skipws()
+        if (pos.end) return Token("", currentPos, Token.Type.EOF)
+        val from = currentPos
+        return when (val ch = pos.currentChar.also { advance() }) {
+            '(' -> Token("(", from, Token.Type.LPAREN)
+            ')' -> Token(")", from, Token.Type.RPAREN)
+            '{' -> Token("{", from, Token.Type.LBRACE)
+            '}' -> Token("}", from, Token.Type.RBRACE)
+            '[' -> Token("[", from, Token.Type.LBRACKET)
+            ']' -> Token("]", from, Token.Type.RBRACKET)
+            ',' -> Token(",", from, Token.Type.COMMA)
+            ';' -> Token(";", from, Token.Type.SEMICOLON)
+            '=' -> Token("=", from, Token.Type.ASSIGN)
+            '+' -> Token("+", from, Token.Type.PLUS)
+            '-' -> Token("-", from, Token.Type.MINUS)
+            '*' -> Token("*", from, Token.Type.STAR)
+            '/' -> Token("/", from, Token.Type.SLASH)
+            '.' -> Token(".", from, Token.Type.DOT)
+            '<' -> Token("<", from, Token.Type.LT)
+            '>' -> Token(">", from, Token.Type.GT)
+            '!' -> Token("!", from, Token.Type.NOT)
+            '"' -> loadStringToken()
+            in digits -> {
+                pos.back()
+                decodeNumber(loadChars(digits), from)
+            }
+            in idFirstChars -> {
+                // it includes first char, so from current position
+                Token(ch + loadChars(idNextChars), from, Token.Type.ID)
+            }
+            else -> raise("can't parse token")
+        }
+    }
+
+    private fun decodeNumber(p1: String, start: Pos): Token =
+        if( pos.end )
+            Token(p1, start, Token.Type.INT)
+        else if( currentChar == '.' ) {
+            // could be decimal
+            advance()
+            if( currentChar in digits ) {
+                // decimal part
+                val p2 = loadChars(digits)
+                // with exponent?
+                if( currentChar == 'e' || currentChar == 'E') {
+                    advance()
+                    var negative = false
+                    if(currentChar == '+' )
+                        advance()
+                    else if(currentChar == '-') {
+                        negative = true
+                        advance()
+                    }
+                    var p3 = loadChars(digits)
+                    if( negative ) p3 = "-$p3"
+                    Token("$p1.${p2}e$p3", start, Token.Type.REAL)
+                }
+                else {
+                    // no exponent
+                    Token("$p1.$p2", start, Token.Type.REAL)
+                }
+            }
+            else {
+                // not decimal
+                // something like 10.times, method call on integer number
+                pos.back()
+                Token(p1, start, Token.Type.INT)
+            }
+        }
+        else {
+            // could be integer, also hex:
+            if (currentChar == 'x' && p1 == "0") {
+                advance()
+                Token(loadChars(hexDigits), start, Token.Type.HEX).also {
+                    if( currentChar.isLetter() )
+                        raise("invalid hex literal")
+                }
+            } else {
+                Token(p1, start, Token.Type.INT)
+            }
+        }
+
+
+    private val currentChar: Char get() = pos.currentChar
+
+    private fun loadStringToken(): Token {
+        var start = currentPos
+
+        if (currentChar == '"') advance()
+        else start = start.back()
+
+        val sb = StringBuilder()
+        while (currentChar != '"') {
+            if( pos.end ) raise("unterminated string")
+            when (currentChar) {
+                '\\' -> {
+                    advance() ?: raise("unterminated string")
+                    when (currentChar) {
+                        'n' -> sb.append('\n')
+                        'r' -> sb.append('\r')
+                        't' -> sb.append('\t')
+                        '"' -> sb.append('"')
+                        else -> sb.append('\\').append(currentChar)
+                    }
+                }
+                else -> {
+                    sb.append(currentChar)
+                    advance()
+                }
+            }
+        }
+        advance()
+        return Token(sb.toString(), start, Token.Type.STRING)
+    }
+
+    /**
+     * Load characters from the set until it reaches EOF or invalid character found.
+     * stop at EOF on character not in [validChars].
+     * @return the string of valid characters, could be empty
+     */
+    private fun loadChars(validChars: Set<Char>): String {
+        val result = StringBuilder()
+        while (!pos.end) {
+            val ch = pos.currentChar
+            if (ch in validChars) {
+                result.append(ch)
+                advance()
+            } else
+                break
+        }
+        return result.toString()
+    }
+
+    /**
+     * next non-whitespace char (newline are skipped too) or null if EOF
+     */
+    private fun skipws(): Char? {
+        while (!pos.end) {
+            val ch = pos.currentChar
+            if (ch.isWhitespace())
+                advance()
+            else
+                return ch
+        }
+        return null
+    }
+
+    private fun advance() = pos.advance()
+
+    init {
+//        advance()
+    }
+}

library/src/commonMain/kotlin/net/sergeych/ling/Pos.kt

@@ -0,0 +1,69 @@
+package net.sergeych.ling
+
+data class Pos(val source: Source, val line: Int, val column: Int) {
+    override fun toString(): String {
+        return "${source.fileName}:$line:$column"
+    }
+
+    fun back(): Pos =
+        if( column > 0) Pos(source, line, column-1)
+        else if( line > 0) Pos(source, line-1, source.lines[line-1].length - 1)
+        else throw IllegalStateException("can't go back from line 0, column 0")
+
+    val currentLine: String get() = source.lines[line]
+
+    val showSource: String by lazy {
+        source.lines[line] + "\n" + "-".repeat(column - 1) + "^\n"
+    }
+
+    companion object {
+        val builtIn = Pos(Source.builtIn, 0, 0)
+    }
+
+}
+
+class MutablePos(private val from: Pos) {
+
+    val lines = from.source.lines
+    var line = from.line
+        private set
+    var column = from.column
+        private set
+
+    val end: Boolean get() =
+        line == lines.size
+
+    fun reset(to: Pos) {
+        line = to.line
+        column = to.column
+    }
+
+    fun toPos(): Pos = Pos(from.source, line, column)
+
+    fun advance(): Char? {
+        if (end) return null
+        val current = lines[line]
+        return if (column+1 < current.length) {
+            current[column++]
+        } else {
+            line++
+            column = 0
+            if(line >= lines.size) null
+            else lines[line][column]
+        }
+    }
+
+    fun back() {
+        if (column > 0) column--
+        else if (line > 0)
+            column = lines[--line].length - 1
+        else throw IllegalStateException("can't go back from line 0, column 0")
+    }
+    val currentChar: Char
+        get() =
+            if (end) 0.toChar()
+            else lines[line][column]
+
+    override fun toString() = "($line:$column)"
+
+}

library/src/commonMain/kotlin/net/sergeych/ling/Script.kt

@@ -0,0 +1,22 @@
+package net.sergeych.ling
+
+class Script(
+    override val pos: Pos,
+    private val statements: List<Statement> = emptyList(),
+) : Statement() {
+
+    override suspend fun execute(context: Context): Obj {
+        // todo: run script
+        var lastResult: Obj = Void
+        for (s in statements) {
+            lastResult = s.execute(context)
+        }
+        return lastResult
+    }
+
+    suspend fun execute() = execute(defaultContext)
+
+    companion object {
+        val defaultContext: Context = Context(Pos.builtIn)
+    }
+}

library/src/commonMain/kotlin/net/sergeych/ling/ScriptError.kt

@@ -0,0 +1,9 @@
+package net.sergeych.ling
+
+class ScriptError(val pos: Pos, val errorMessage: String) : Exception(
+    """
+        $pos: Error: $errorMessage
+        ${pos.currentLine}
+        ${"-".repeat(pos.column)}^
+    """.trimIndent()
+)

library/src/commonMain/kotlin/net/sergeych/ling/Source.kt

@@ -0,0 +1,14 @@
+package net.sergeych.ling
+
+class Source(val fileName: String, text: String) {
+
+    val lines = text.lines().map { it.trimEnd() }
+
+    companion object {
+        val builtIn: Source by lazy { Source("built-in", "") }
+    }
+
+    val startPos: Pos = Pos(this, 0, 0)
+
+    fun posAt(line: Int, column: Int): Pos = Pos(this, line, column)
+}

library/src/commonMain/kotlin/net/sergeych/ling/Token.kt

@@ -0,0 +1,12 @@
+package net.sergeych.ling
+
+data class Token(val value: String, val pos: Pos, val type: Type) {
+    enum class Type {
+        ID, INT, REAL, HEX, STRING, LPAREN, RPAREN, LBRACE, RBRACE, LBRACKET, RBRACKET, COMMA,
+        SEMICOLON, COLON, EQ, PLUS, MINUS, STAR, SLASH, ASSIGN, EQEQ, NEQ, LT, LTEQ, GT,
+        GTEQ, AND, OR, NOT, DOT, ARROW, QUESTION, COLONCOLON, EOF,
+    }
+    companion object {
+//        fun eof(parser: Parser) = Token("", parser.currentPos, Type.EOF)
+    }
+}

library/src/commonMain/kotlin/net/sergeych/ling/statements.kt

@@ -0,0 +1,117 @@
+package net.sergeych.ling
+
+fun String.toSource(name: String = "eval"): Source = Source(name, this)
+
+
+abstract class Statement : Obj() {
+    abstract val pos: Pos
+    abstract suspend fun execute(context: Context): Obj
+}
+
+fun Statement.raise(text: String): Nothing {
+    throw ScriptError(pos, text)
+}
+
+fun Statement.require(cond: Boolean, message: () -> String) {
+    if (!cond) raise(message())
+}
+
+fun statement(pos: Pos, f: suspend (Context) -> Obj): Statement = object : Statement() {
+    override val pos: Pos = pos
+    override suspend fun execute(context: Context): Obj = f(context)
+}
+
+class IfStatement(
+    override val pos: Pos,
+    val cond: Statement, val ifTrue: Statement, val ifFalse: Statement?
+) : Statement() {
+    override suspend fun execute(context: Context): Obj {
+        val c = cond.execute(context)
+        if (c !is ObjBool)
+            raise("if: condition must me boolean, got: $c")
+
+        return if (c.value) ifTrue.execute(context) else ifFalse?.execute(context) ?: Void
+    }
+}
+
+class LogicalAndStatement(
+    override val pos: Pos,
+    val left: Statement, val right: Statement
+) : Statement() {
+    override suspend fun execute(context: Context): Obj {
+
+        val l = left.execute(context).let {
+            (it as? ObjBool) ?: raise("logical and: left operand is not boolean: $it")
+        }
+        val r = right.execute(context).let {
+            (it as? ObjBool) ?: raise("logical and: right operand is not boolean: $it")
+        }
+        return ObjBool(l.value && r.value)
+    }
+}
+
+class PlusStatement(
+    override val pos: Pos,
+    val left: Statement, val right: Statement
+) : Statement() {
+    override suspend fun execute(context: Context): Obj {
+        // todo: implement also classes with 'plus' operator
+        val l = left.execute(context)
+
+        if (l is ObjString)
+            return ObjString(l.toString() + right.execute(context).toString())
+
+        if (l !is Numeric)
+            raise("left operand is not number: $l")
+
+        val r = right.execute(context)
+        if (r !is Numeric)
+            raise("right operand is not boolean: $r")
+
+        return if (l is ObjInt && r is ObjInt)
+            ObjInt(l.longValue + r.longValue)
+        else
+            ObjReal(l.doubleValue + r.doubleValue)
+    }
+}
+
+class MinusStatement(
+    override val pos: Pos,
+    val left: Statement, val right: Statement
+) : Statement() {
+    override suspend fun execute(context: Context): Obj {
+        // todo: implement also classes with 'minus' operator
+        val l = left.execute(context)
+        if (l !is Numeric)
+            raise("left operand is not number: $l")
+
+        val r = right.execute(context)
+        if (r !is Numeric)
+            raise("right operand is not number: $r")
+
+        return if (l is ObjInt && r is ObjInt)
+            ObjInt(l.longValue - r.longValue)
+        else
+            ObjReal(l.doubleValue - r.doubleValue)
+    }
+}
+
+class AssignStatement(override val pos: Pos, val name: String, val value: Statement) : Statement() {
+    override suspend fun execute(context: Context): Obj {
+        val variable = context[name] ?: raise("can't assign: variable does not exist: $name")
+        variable.value = value.execute(context)
+        return Void
+    }
+}
+
+class CallStatement(
+    override val pos: Pos,
+    val name: String,
+    val args: Arguments = Arguments.EMPTY
+) : Statement() {
+    override suspend fun execute(context: Context): Obj {
+        val callee = context[name] ?: raise("Call: unknown name: $name")
+        return (callee.value as? Statement)?.execute(context.copy(pos, args))
+            ?: raise("Call: not a callable object: $callee")
+    }
+}

library/src/commonTest/kotlin/ScriptTest.kt

@@ -0,0 +1,112 @@
+package io.github.kotlin.fibonacci
+
+import kotlinx.coroutines.test.runTest
+import net.sergeych.ling.*
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class ScriptTest {
+
+    @Test
+    fun level0() = runTest {
+        val s = Script(
+            Pos.builtIn,
+            listOf(
+                CallStatement(
+                    Pos.builtIn, "println",
+                    Arguments(listOf(CallStatement(Pos.builtIn, "π", Arguments.EMPTY)))
+                )
+            )
+        )
+        s.execute(basicContext)
+    }
+
+    fun parseFirst(str: String): Token =
+        parseLing(str.toSource()).firstOrNull()!!
+
+    @Test
+    fun parseNumbers() {
+        fun check(expected: String, type: Token.Type, row: Int, col: Int, src: String, offset: Int = 0) {
+            val source = src.toSource()
+            assertEquals(
+                Token(expected, source.posAt(row, col), type),
+                parseLing(source)[offset]
+            )
+        }
+        check("1", Token.Type.INT, 0, 0, "1")
+        check("7", Token.Type.INT, 0, 0, "7")
+        check("17", Token.Type.INT, 0, 0, "17")
+        check("17", Token.Type.INT, 0, 0, "17.")
+        check(".", Token.Type.DOT, 0, 2, "17.", 1)
+
+        // decimals
+        check("17.2", Token.Type.REAL, 0, 0, "17.2")
+        check("17.2", Token.Type.REAL, 0, 0, "17.2")
+        check("17.2", Token.Type.REAL, 0, 0, "17.2 ")
+        check("17.2", Token.Type.REAL, 0, 1, " 17.2")
+        check("17.2", Token.Type.REAL, 0, 2, "  17.2  ")
+        check("17.2e0", Token.Type.REAL, 0, 0, "17.2e0")
+        check("17.2e-22", Token.Type.REAL, 0, 0, "17.2e-22")
+        check("17.2e22", Token.Type.REAL, 0, 0, "17.2e+22")
+        check("17.2e22", Token.Type.REAL, 0, 0, "17.2E+22")
+        check("17.2e22", Token.Type.REAL, 0, 0, "17.2E22")
+        check("17.2e-22", Token.Type.REAL, 0, 0, "17.2E-22")
+
+        // hex
+        check("1", Token.Type.HEX, 0, 0, "0x1")
+        check("12", Token.Type.HEX, 0, 0, "0x12")
+        check("12abcdef", Token.Type.HEX, 0, 0, "0x12abcdef.gh")
+        check(".", Token.Type.DOT, 0, 10, "0x12abcdef.gh", 1)
+        check("gh", Token.Type.ID, 0, 11, "0x12abcdef.gh", 2)
+
+        check("5", Token.Type.INT, 0, 0, "5 6")
+        check("6", Token.Type.INT, 0, 2, "5 6", 1)
+
+    }
+
+    @Test
+    fun parse0() {
+        val src = """
+            println("Hello")
+            println( "world" )
+        """.trimIndent().toSource()
+
+        val p = parseLing(src).listIterator()
+
+        assertEquals(Token("println", src.posAt(0, 0), Token.Type.ID), p.next())
+        assertEquals(Token("(", src.posAt(0, 7), Token.Type.LPAREN), p.next())
+        assertEquals(Token("Hello", src.posAt(0, 8), Token.Type.STRING), p.next())
+        assertEquals(Token(")", src.posAt(0, 15), Token.Type.RPAREN), p.next())
+
+        assertEquals(Token("println", src.posAt(1, 0), Token.Type.ID), p.next())
+        assertEquals(Token("(", src.posAt(1, 7), Token.Type.LPAREN), p.next())
+        assertEquals(Token("world", src.posAt(1, 9), Token.Type.STRING), p.next())
+        assertEquals(Token(")", src.posAt(1, 17), Token.Type.RPAREN), p.next())
+    }
+
+    @Test
+    fun parse1() {
+        val src = "2 + 7".toSource()
+
+        val p = parseLing(src).listIterator()
+
+        assertEquals(Token("2", src.posAt(0, 0), Token.Type.INT), p.next())
+        assertEquals(Token("+", src.posAt(0, 2), Token.Type.PLUS), p.next())
+        assertEquals(Token("7", src.posAt(0, 4), Token.Type.INT), p.next())
+    }
+
+    @Test
+    fun compileNumbers() = runTest {
+        assertEquals(ObjInt(17), eval("17"))
+        assertEquals(ObjInt(17), eval("+17"))
+        assertEquals(ObjInt(-17), eval("-17"))
+
+
+        assertEquals(ObjInt(1970), eval("1900 + 70"))
+        assertEquals(ObjInt(1970), eval("2000 - 30"))
+
+//        assertEquals(ObjReal(3.14), eval("3.14"))
+        assertEquals(ObjReal(314.0), eval("3.14e2"))
+    }
+
+}