Implemented Blocks and Assignments

src/main/ExprGenerator.ws.kts

@@ -40,15 +40,19 @@ fun defineAst(baseName: String, types: List<String>) {
 }
 
 val exprTypes = listOf(
+    "Assign   : Token name, Expr value",
     "Binary   : Expr left, Token operator, Expr right",
     "Grouping : Expr expression",
     "Literal  : Any? value",
-    "Unary    : Token operator, Expr right"
+    "Unary    : Token operator, Expr right",
+    "Variable : Token name"
 )
 defineAst("Expr", exprTypes)
 
 val stmtTypes = listOf(
+    "Block : List<Stmt?> statements",
     "Expression : Expr expression",
-    "Print      : Expr expression"
+    "Print      : Expr expression",
+    "Var        : Token name, Expr? initializer"
 )
 defineAst("Stmt", stmtTypes)

src/main/fr/celticinfo/lox/AstPrinter.kt

@@ -5,20 +5,28 @@ class AstPrinter : ExprVisitor<String> {
         return expr.accept(this)
     }
 
-    override fun visitBinary(binary: Binary): String {
-        return parenthesize(binary.operator.lexeme, binary.left, binary.right)
+    override fun visitAssign(expr: Assign): String {
+        return parenthesize("=", expr)
     }
 
-    override fun visitGrouping(grouping: Grouping): String {
-        return parenthesize("group", grouping.expression)
+    override fun visitBinary(expr: Binary): String {
+        return parenthesize(expr.operator.lexeme, expr.left, expr.right)
     }
 
-    override fun visitLiteral(literal: Literal): String {
-        return literal.value?.toString() ?: "nil"
+    override fun visitGrouping(expr: Grouping): String {
+        return parenthesize("group", expr.expression)
     }
 
-    override fun visitUnary(unary: Unary): String {
-        return parenthesize(unary.operator.lexeme, unary.right)
+    override fun visitLiteral(expr: Literal): String {
+        return expr.value?.toString() ?: "nil"
+    }
+
+    override fun visitUnary(expr: Unary): String {
+        return parenthesize(expr.operator.lexeme, expr.right)
+    }
+
+    override fun visitVariable(expr: Variable): String {
+        return expr.name.lexeme
     }
     
     private fun parenthesize(name: String, vararg exprs: Expr): String {

src/main/fr/celticinfo/lox/Environment.kt

@@ -0,0 +1,47 @@
+package fr.celticinfo.lox
+
+/**
+ * The Environment class is used to store the variables and their values.
+ */
+class Environment {
+    private val enclosing: Environment?
+    private val values = mutableMapOf<String, Any?>()
+
+    constructor() {
+        enclosing = null
+    }
+
+    constructor(enclosing: Environment) {
+        this.enclosing = enclosing
+    }
+
+    fun define(name: String, value: Any?) {
+        values[name] = value
+    }
+
+    fun get(name: Token): Any? {
+        if (values.containsKey(name.lexeme)) {
+            return values[name.lexeme]
+        }
+
+        if (enclosing != null) {
+            return enclosing.get(name)
+        }
+
+        throw RuntimeError(name, "Undefined variable '${name.lexeme}'.")
+    }
+
+    fun assign(name: Token, value: Any?) {
+        if (values.containsKey(name.lexeme)) {
+            values[name.lexeme] = value
+            return
+        }
+
+        if (enclosing != null) {
+            enclosing.assign(name, value)
+            return
+        }
+
+        throw RuntimeError(name, "Undefined variable '${name.lexeme}'.")
+    }
+}

src/main/fr/celticinfo/lox/Expr.kt

@@ -4,10 +4,12 @@ package fr.celticinfo.lox
  * The ExprVisitor interface is used to visit the different types of expressions that can be parsed by the Parser.
  */
 interface ExprVisitor<R> {
+    fun visitAssign(expr: Assign): R
     fun visitBinary(expr: Binary): R
     fun visitGrouping(expr: Grouping): R
     fun visitLiteral(expr: Literal): R
     fun visitUnary(expr: Unary): R
+    fun visitVariable(expr: Variable): R
 }
 
 /**
@@ -17,6 +19,15 @@ sealed class Expr {
     abstract fun <R> accept(visitor: ExprVisitor<R>): R
 }
 
+data class Assign(
+    val name: Token,
+    val value: Expr
+) : Expr() {
+    override fun <R> accept(visitor: ExprVisitor<R>): R {
+        return visitor.visitAssign(this)
+    }
+}
+
 data class Binary(
     val left: Expr, val operator: Token, val right: Expr
 ) : Expr() {
@@ -48,3 +59,11 @@ data class Unary(
         return visitor.visitUnary(this)
     }
 }
+
+data class Variable(
+    val name: Token
+) : Expr() {
+    override fun <R> accept(visitor: ExprVisitor<R>): R {
+        return visitor.visitVariable(this)
+    }
+}

src/main/fr/celticinfo/lox/Interpreter.kt

@@ -3,8 +3,9 @@ package fr.celticinfo.lox
 import fr.celticinfo.lox.TokenType.*
 
 class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
+    private var environment = Environment()
 
-    fun interpret(statements: List<Stmt>) {
+    fun interpret(statements: List<Stmt?>) {
         try {
             for (statement in statements) {
                 execute(statement)
@@ -15,12 +16,28 @@ class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
         }
     }
 
-    private fun execute(stmt: Stmt) {
-        stmt.accept(this)
+    private fun execute(stmt: Stmt?) {
+        stmt?.accept(this)
     }
 
-    private fun evaluate(expr: Expr): Any? {
-        return expr.accept(this)
+    override fun visitBlock(stmt: Block) {
+        executeBlock(stmt.statements, Environment(environment))
+    }
+
+    private fun executeBlock(statements: List<Stmt?>, environment: Environment) {
+        val previous = this.environment
+        try {
+            this.environment = environment
+            for (statement in statements) {
+                execute(statement)
+            }
+        } finally {
+            this.environment = previous
+        }
+    }
+
+    private fun evaluate(expr: Expr?): Any? {
+        return expr?.accept(this)
     }
 
     override fun visitExpression(stmt: Expression) {
@@ -32,6 +49,17 @@ class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
         println(stringify(value))
     }
 
+    override fun visitVar(stmt: Var) {
+        val value = evaluate(stmt.initializer)
+        environment.define(stmt.name.lexeme, value)
+    }
+
+    override fun visitAssign(expr: Assign): Any? {
+        val value = evaluate(expr.value)
+        environment.assign(expr.name, value)
+        return value
+    }
+
     override fun visitBinary(expr: Binary): Any? {
         val left = evaluate(expr.left)
         val right = evaluate(expr.right)
@@ -104,6 +132,10 @@ class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
         }
     }
 
+    override fun visitVariable(expr: Variable): Any? {
+        return environment.get(expr.name)
+    }
+
     private fun isTruthy(obj: Any?): Boolean {
         return when (obj) {
             null -> false

src/main/fr/celticinfo/lox/Parser.kt

@@ -10,18 +10,44 @@ import fr.celticinfo.lox.TokenType.*
 class Parser(private val tokens: List<Token>) {
     private var current = 0
 
-    fun parse(): List<Stmt> {
-        val statements: MutableList<Stmt> = ArrayList()
+    fun parse(): List<Stmt?> {
+        val statements: MutableList<Stmt?> = ArrayList()
         while (!isAtEnd()) {
-            statements.add(statement())
+            statements.add(declaration())
         }
 
         return statements
     }
 
+    private fun declaration(): Stmt? {
+        return try {
+            when {
+                match(VAR) -> varDeclaration()
+                else -> statement()
+            }
+        } catch (error: ParseError) {
+            synchronize()
+            return null
+        }
+    }
+    
+    private fun varDeclaration(): Stmt {
+        val name = consume(IDENTIFIER, "Expect variable name.")
+
+        var initializer: Expr? = null
+        if (match(EQUAL)) {
+            initializer = expression()
+        }
+
+        consume(SEMICOLON, "Expect ';' after variable declaration.")
+        return Var(name, initializer)
+    }
+
+
     private fun statement(): Stmt {
         return when {
             match(PRINT) -> printStatement()
+            match(LEFT_BRACE) -> Block(blockStatement())
             else -> expressionStatement()
         }
     }
@@ -34,12 +60,41 @@ class Parser(private val tokens: List<Token>) {
 
     private fun expressionStatement(): Stmt {
         val value = expression()
-        consume(SEMICOLON, "Expect ';' after value.")
+        consume(SEMICOLON, "Expect ';' after expression.")
         return Expression(value)
     }
 
+    private fun blockStatement(): List<Stmt?> {
+        val statements: MutableList<Stmt?> = ArrayList()
+
+        while (!check(RIGHT_BRACE) && !isAtEnd()) {
+            statements.add(declaration())
+        }
+
+        consume(RIGHT_BRACE, "Expect '}' after block.")
+        return statements
+    }
+
     private fun expression(): Expr {
-        return equality()
+        return assignment()
+    }
+
+    private fun assignment(): Expr {
+        val expr = equality()
+
+        if (match(EQUAL)) {
+            val equals = previous()
+            val value = assignment()
+
+            if (expr is Variable) {
+                val name = expr.name
+                return Assign(name, value)
+            }
+
+            error(equals, "Invalid assignment target.")
+        }
+
+        return expr
     }
 
     private fun equality(): Expr {
@@ -116,6 +171,7 @@ class Parser(private val tokens: List<Token>) {
             match(TRUE) -> return Literal(true)
             match(NIL) -> return Literal(null)
             match(NUMBER, STRING) -> return Literal(previous().literal)
+            match(IDENTIFIER) -> return Variable(previous())
             match(LEFT_PAREN) -> {
                 val expr = expression()
                 consume(RIGHT_PAREN, "Expect ')' after expression.")

src/main/fr/celticinfo/lox/Stmt.kt

@@ -4,8 +4,10 @@ package fr.celticinfo.lox
  * The StmtVisitor interface is used to visit the different types of statements that can be parsed by the Parser.
  */
 interface StmtVisitor<R> {
+    fun visitBlock(stmt: Block): R
     fun visitExpression(stmt: Expression): R
     fun visitPrint(stmt: Print): R
+    fun visitVar(stmt: Var): R    
 }
 
 /**
@@ -15,6 +17,14 @@ sealed class Stmt {
     abstract fun <R> accept(visitor: StmtVisitor<R>): R
 }
 
+data class Block(
+    val statements: List<Stmt?>
+) : Stmt() {
+    override fun <R> accept(visitor: StmtVisitor<R>): R {
+        return visitor.visitBlock(this)
+    }
+}
+
 data class Expression(
     val expression: Expr
 ) : Stmt() {
@@ -30,3 +40,12 @@ data class Print(
         return visitor.visitPrint(this)
     }
 }
+
+data class Var(
+    val name: Token,
+    val initializer: Expr?
+) : Stmt() {
+    override fun <R> accept(visitor: StmtVisitor<R>): R {
+        return visitor.visitVar(this)
+    }
+}

src/main/fr/celticinfo/loxext/RpnPrinter.kt

@@ -7,20 +7,28 @@ class RpnPrinter : ExprVisitor<String> {
         return expr.accept(this)
     }
 
-    override fun visitBinary(binary: Binary): String {
-        return stack(binary.operator.lexeme, binary.left, binary.right)
+    override fun visitAssign(expr: Assign): String {
+        return stack("=", expr)
     }
 
-    override fun visitGrouping(grouping: Grouping): String {
-        return stack("", grouping.expression)
+    override fun visitBinary(expr: Binary): String {
+        return stack(expr.operator.lexeme, expr.left, expr.right)
     }
 
-    override fun visitLiteral(literal: Literal): String {
-        return literal.value?.toString() ?: "nil"
+    override fun visitGrouping(expr: Grouping): String {
+        return stack("", expr.expression)
     }
 
-    override fun visitUnary(unary: Unary): String {
-        return stack(unary.operator.lexeme, unary.right)
+    override fun visitLiteral(expr: Literal): String {
+        return expr.value?.toString() ?: "nil"
+    }
+
+    override fun visitUnary(expr: Unary): String {
+        return stack(expr.operator.lexeme, expr.right)
+    }
+
+    override fun visitVariable(expr: Variable): String {
+        return expr.name.lexeme
     }
 
     private fun stack(name: String, vararg exprs: Expr): String {

src/test/fr/celticinfo/lox/InterpreterTest.kt

@@ -1,8 +1,11 @@
 package fr.celticinfo.lox
 
 import fr.celticinfo.loxext.RpnPrinter
-import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertDoesNotThrow
+import java.io.ByteArrayOutputStream
+import java.io.PrintStream
 import kotlin.test.*
+import kotlin.test.Test
 
 class InterpreterTest {
 
@@ -57,4 +60,145 @@ class InterpreterTest {
             }
         )
     }
+
+    @Test
+    fun `Shadowing a variable should not raise error`() {
+        val code = """
+            var a = 1;
+            {
+                var a = 2;
+            }
+            print a;
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(3, statements.size)
+
+        assertDoesNotThrow {
+            Interpreter().interpret(statements)
+        }
+    }
+
+    @Test
+    fun `Variable reassignment should not raise error`() {
+        val code = """
+            var a = 1;
+            a = 2;
+            print a;
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(3, statements.size)
+
+        assertDoesNotThrow {
+            Interpreter().interpret(statements)
+        }
+    }
+
+    @Test
+    fun `Variable reassignment with different type should not raise error`() {
+        val code = """
+            var a = 1;
+            a = false;
+            print a;
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(3, statements.size)
+
+        assertDoesNotThrow {
+            Interpreter().interpret(statements)
+        }
+    }
+
+    @Test
+    fun `Variable shadowing should not raise error`() {
+        val code = """
+            var a = 1;
+            {
+                var a = false;
+                print a;
+            }
+            print a;
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(3, statements.size)
+
+        assertDoesNotThrow {
+            Interpreter().interpret(statements)
+        }
+    }
+
+    @Test
+    fun `Variable shadowing with different type should not raise error`() {
+        val code = """
+            var a = 1;
+            {
+                var a = false;
+                print a;
+            }
+            print a;
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(3, statements.size)
+
+        assertDoesNotThrow {
+            Interpreter().interpret(statements)
+        }
+    }
+
+    @Test
+    fun `Variable shadowing should work with block`() {
+        val standardOut = System.out
+        val outputStreamCaptor = ByteArrayOutputStream()
+
+        System.setOut(PrintStream(outputStreamCaptor))
+
+        try {
+            val code = """
+var a = "global a";
+var b = "global b";
+var c = "global c";
+{
+  var a = "outer a";
+  var b = "outer b";
+  {
+    var a = "inner a";
+    print a;
+    print b;
+    print c;
+  }
+  print a;
+  print b;
+  print c;
+}
+print a;
+print b;
+print c;
+            """.trimIndent()
+            val scanner = Scanner(code)
+            val tokens = scanner.scanTokens()
+            val parser = Parser(tokens)
+            val statements = parser.parse()
+            assertEquals(7, statements.size)
+
+            Interpreter().interpret(statements)
+            val output = outputStreamCaptor.toString().trim()
+            assertEquals("inner a\nouter b\nglobal c\nouter a\nouter b\nglobal c\nglobal a\nglobal b\nglobal c", output)
+        } finally {
+            System.setOut(standardOut)
+        }
+    }
 }

src/test/fr/celticinfo/lox/ParserTest.kt

@@ -1,8 +1,9 @@
 package fr.celticinfo.lox
 
 import fr.celticinfo.loxext.RpnPrinter
-import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertAll
 import kotlin.test.*
+import kotlin.test.Test
 
 class ParserTest {
     @Test
@@ -29,12 +30,10 @@ class ParserTest {
         val scanner = Scanner(code)
         val tokens = scanner.scanTokens()
         val parser = Parser(tokens)
-
-        assertFailsWith<Parser.ParseError>(
-            block = {
-                parser.parse()
-            }
-        )
+        val statements = parser.parse()
+        assertEquals(1,statements.size)
+        val stmt = statements.first()
+        assertNull(stmt)
     }
 
     @Test
@@ -45,11 +44,86 @@ class ParserTest {
         val scanner = Scanner(code)
         val tokens = scanner.scanTokens()
         val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(1,statements.size)
+        val stmt = statements.first()
+        assertNull(stmt)
+    }
+
+    @Test
+    fun `valid code with multiple statements`() {
+        val code = """
+            var a = 1;
+            var b = 2;
+            print a + b;
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(3,statements.size)
+        assertAll(
+            { assertTrue(statements[0] is Var) },
+            { assertTrue(statements[1] is Var) },
+            { assertTrue(statements[2] is Print) }
+        )
+    }
 
-        assertFailsWith<Parser.ParseError>(
-            block = {
-                parser.parse()
+    @Test
+    fun `valid code with block`() {
+        val code = """
+            {
+                var a = 1;
+                var b = 2;
+                print a + b;
             }
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(1,statements.size)
+        val stmt = statements.first()
+        assertTrue(stmt is Block)
+        val block = stmt.statements
+        assertEquals(3,block.size)
+        assertAll(
+            { assertTrue(block[0] is Var) },
+            { assertTrue(block[1] is Var) },
+            { assertTrue(block[2] is Print) }
+        )
+    }
+
+    @Test
+    fun `valid code with block and nested block`() {
+        val code = """
+            {
+                var a = 1;
+                {
+                    var b = 2;
+                    print a + b;
+                }
+            }
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(1,statements.size)
+        val stmt = statements.first()
+        assertTrue(stmt is Block)
+        val block = stmt.statements
+        assertEquals(2,block.size)
+        assertAll(
+            { assertTrue(block[0] is Var) },
+            { assertTrue(block[1] is Block) }
+        )
+        val nestedBlock = block[1] as Block
+        val nestedStatements = nestedBlock.statements
+        assertEquals(2,nestedStatements.size)
+        assertAll(
+            { assertTrue(nestedStatements[0] is Var) },
+            { assertTrue(nestedStatements[1] is Print) }
         )
     }
 }