+var and val

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

@@ -61,14 +61,15 @@ class Compiler {
     }
 
     private fun parseStatement(tokens: ListIterator<Token>): Statement? {
+        while(true) {
             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) {
+                    if (next.type == Token.Type.ASSIGN) {
                         // this _is_ assignment statement
-                    AssignStatement(
+                        return AssignStatement(
                             t.pos, t.value,
                             parseExpression(tokens) ?: throw ScriptError(
                                 t.pos,
@@ -87,6 +88,8 @@ class Compiler {
                         }
                 }
 
+                Token.Type.SEMICOLON -> continue
+
                 Token.Type.EOF -> null
 
                 else -> {
@@ -96,6 +99,7 @@ class Compiler {
                 }
             }
         }
+    }
 
     private fun parseExpression(tokens: ListIterator<Token>, level: Int = 0): Statement? {
         if (level == lastLevel)
@@ -243,9 +247,37 @@ class Compiler {
      * Parse keyword-starting statenment.
      * @return parsed statement or null if, for example. [id] is not among keywords
      */
-    @Suppress("UNUSED_PARAMETER")
+    private fun parseKeywordStatement(id: Token, tokens: ListIterator<Token>): Statement?
-    private fun parseKeywordStatement(id: Token, tokens: ListIterator<Token>): Statement? {
+    = when (id.value) {
-        return null
+        "val" -> parseVarDeclaration(id.value, false, tokens)
+        "var" -> parseVarDeclaration(id.value, true, tokens)
+        else -> null
+    }
+
+    private fun parseVarDeclaration(kind: String, mutable: Boolean, tokens: ListIterator<Token>): Statement {
+        val nameToken = tokens.next()
+        if( nameToken.type != Token.Type.ID)
+            throw ScriptError(nameToken.pos, "Expected identifier after '$kind'")
+        val name = nameToken.value
+        val eqToken = tokens.next()
+        var setNull = false
+        if( eqToken.type != Token.Type.ASSIGN) {
+            if( !mutable )
+                throw ScriptError(eqToken.pos, "Expected initializator: '=' after '$kind ${name}'")
+            else {
+                tokens.previous()
+                setNull = true
+            }
+        }
+        val initialExpression = if( setNull ) null else parseExpression(tokens)
+            ?: throw ScriptError(eqToken.pos, "Expected initializer expression")
+        return statement(nameToken.pos) { context ->
+            if( context.containsLocal(name) )
+                throw ScriptError(nameToken.pos, "Variable $name is already defined")
+            val initValue = initialExpression?.execute(context) ?: ObjNull
+            context.addItem(name, mutable, initValue)
+            ObjVoid
+        }
     }
 
 //    fun parseStatement(parser: Parser): Statement? =

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

@@ -1,7 +1,7 @@
 package net.sergeych.ling
 
 class Context(
-    val parent: Context? = null,
+    val parent: Context? = Script.defaultContext.copy(),
     val args: Arguments = Arguments.EMPTY
 ) {
 
@@ -58,6 +58,11 @@ class Context(
         }
     }
 
+    suspend fun eval(code: String): Obj =
+        Compiler().compile(code.toSource()).execute(this)
+
+    fun containsLocal(name: String): Boolean = name in objects
+
     companion object {
         operator fun invoke() = Context()
     }

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

@@ -69,6 +69,7 @@ fun Obj.toLong(): Long =
         ?: (this as? ObjString)?.value?.toLong()
         ?: throw IllegalArgumentException("cannot convert to double $this")
 
+fun Obj.toInt(): Int = toLong().toInt()
 
 
 @Serializable

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

@@ -41,7 +41,14 @@ private class Parser(fromPos: Pos) {
             ']' -> Token("]", from, Token.Type.RBRACKET)
             ',' -> Token(",", from, Token.Type.COMMA)
             ';' -> Token(";", from, Token.Type.SEMICOLON)
-            '=' -> Token("=", from, Token.Type.ASSIGN)
+            '=' -> {
+                if( pos.currentChar == '=') {
+                    advance()
+                    Token("==", from, Token.Type.EQ)
+                }
+                else
+                    Token("=", from, Token.Type.ASSIGN)
+            }
             '+' -> Token("+", from, Token.Type.PLUS)
             '-' -> Token("-", from, Token.Type.MINUS)
             '*' -> Token("*", from, Token.Type.STAR)

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

@@ -20,7 +20,7 @@ class Script(
     suspend fun execute() = execute(defaultContext)
 
     companion object {
-        val defaultContext: Context = Context().apply {
+        val defaultContext: Context = Context(null).apply {
             addFn("println") {
                 require(args.size == 1)
                 println(args[0].asStr.value)

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

@@ -87,6 +87,8 @@ class MinusStatement(
 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")
+        if( !variable.isMutable )
+            throw ScriptError(pos,"can't reassign val $name")
         variable.value = value.execute(context)
         return ObjVoid
     }

library/src/commonTest/kotlin/ScriptTest.kt

@@ -3,10 +3,7 @@ package io.github.kotlin.fibonacci
 import kotlinx.coroutines.test.runTest
 import net.sergeych.ling.*
 import kotlin.math.PI
-import kotlin.test.Test
+import kotlin.test.*
-import kotlin.test.assertEquals
-import kotlin.test.assertIs
-import kotlin.test.assertTrue
 
 class ScriptTest {
 
@@ -109,4 +106,30 @@ class ScriptTest {
         assertTrue(eval("sin(π)").toDouble() - 1 < 0.000001)
     }
 
+    @Test
+    fun varsAndConsts() = runTest {
+        val context = Context()
+        assertEquals(ObjVoid,context.eval("""
+            val a = 17
+            var b = 3
+        """.trimIndent()))
+        assertEquals(17, context.eval("a").toInt())
+        assertEquals(20, context.eval("b + a").toInt())
+        assertFailsWith<ScriptError> {
+            context.eval("a = 10")
+        }
+        assertEquals(10, context.eval("b = a - 3 - 4; b").toInt())
+        assertEquals(10, context.eval("b").toInt())
+    }
+
+//    @Test
+//    fun functionTest() = runTest {
+//        val context = Context()
+//        context.eval("""
+//            fun foo(a, b) {
+//                a + b
+//            }
+//        """.trimIndent())
+//    }
+
 }