Add class declarations

src/main/ExprGenerator.ws.kts

@@ -52,7 +52,8 @@ val exprTypes = listOf(
 defineAst("Expr", exprTypes)
 
 val stmtTypes = listOf(
-    "Block : List<Stmt?> statements",
+    "Block      : List<Stmt?> statements",
+    "ClassStmt  : Token name, List<Function> methods",
     "Expression : Expr expression",
     "Function   : Token name, List<Token> params, List<Stmt?> body",
     "If         : Expr condition, Stmt thenBranch, Stmt? elseBranch",

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

@@ -46,20 +46,10 @@ class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
         executeBlock(stmt.statements, Environment(environment))
     }
 
-    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 visitClassStmt(stmt: ClassStmt) {
+        environment.define(stmt.name.lexeme, null)
+        val klass = LoxClass(stmt.name.lexeme)
+        environment.assign(stmt.name, klass)
     }
 
     override fun visitExpression(stmt: Expression) {
@@ -215,6 +205,22 @@ class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
         return lookUpVariable(expr.name, expr)
     }
 
+    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)
+    }
+
     private fun lookUpVariable(name: Token, expr: Expr): Any? {
         val distance = locals[expr]
         return if (distance != null) {

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

@@ -0,0 +1,5 @@
+package fr.celticinfo.lox
+
+class LoxClass(val name: String) {
+    override fun toString() = name
+}

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

@@ -22,6 +22,7 @@ class Parser(private val tokens: List<Token>) {
     private fun declaration(): Stmt? {
         return try {
             when {
+                match(CLASS) -> classDeclaration()
                 match(FUN) -> function("function")
                 match(VAR) -> varDeclaration()
                 else -> statement()
@@ -32,7 +33,21 @@ class Parser(private val tokens: List<Token>) {
         }
     }
 
-    private fun function(kind: String): Stmt {
+    private fun classDeclaration(): ClassStmt {
+        val name = consume(IDENTIFIER, "Expect class name.")
+        consume(LEFT_BRACE, "Expect '{' before class body.")
+
+        val methods: MutableList<Function> = ArrayList()
+        while (!check(RIGHT_BRACE) && !isAtEnd()) {
+            methods.add(function("method"))
+        }
+
+        consume(RIGHT_BRACE, "Expect '}' after class body.")
+
+        return ClassStmt(name, methods)
+    }
+
+    private fun function(kind: String): Function {
         val name = consume(IDENTIFIER, "Expect $kind name.")
         consume(LEFT_PAREN, "Expect '(' after $kind name.")
         val parameters: MutableList<Token> = ArrayList()
@@ -51,7 +66,7 @@ class Parser(private val tokens: List<Token>) {
         return Function(name, parameters, body)
     }
 
-    private fun varDeclaration(): Stmt {
+    private fun varDeclaration(): Var {
         val name = consume(IDENTIFIER, "Expect variable name.")
 
         var initializer: Expr? = null
@@ -63,7 +78,7 @@ class Parser(private val tokens: List<Token>) {
         return Var(name, initializer)
     }
 
-    private fun whileStatement(): Stmt {
+    private fun whileStatement(): While {
         consume(LEFT_PAREN, "Expect '(' after 'while'.")
         val condition = expression()
         consume(RIGHT_PAREN, "Expect ')' after condition.")
@@ -120,7 +135,7 @@ class Parser(private val tokens: List<Token>) {
         return body
     }
 
-    private fun ifStatement(): Stmt {
+    private fun ifStatement(): If {
         consume(LEFT_PAREN, "Expect '(' after 'if'.")
         val condition = expression()
         consume(RIGHT_PAREN, "Expect ')' after if condition.")
@@ -135,20 +150,20 @@ class Parser(private val tokens: List<Token>) {
         return If(condition, thenBranch, elseBranch)
     }
 
-    private fun printStatement(): Stmt {
+    private fun printStatement(): Print {
         val value = expression()
         consume(SEMICOLON, "Expect ';' after value.")
         return Print(value)
     }
 
-    private fun returnStatement(): Stmt {
+    private fun returnStatement(): Return {
         val keyword = previous()
         val value = if (!check(SEMICOLON)) expression() else null
         consume(SEMICOLON, "Expect ';' after return value.")
         return Return(keyword, value)
     }
 
-    private fun expressionStatement(): Stmt {
+    private fun expressionStatement(): Expression {
         val value = expression()
         consume(SEMICOLON, "Expect ';' after expression.")
         return Expression(value)

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

@@ -17,6 +17,11 @@ class Resolver(private val interpreter: Interpreter) : ExprVisitor<Unit>, StmtVi
           endScope()
      }
 
+    override fun visitClassStmt(stmt: ClassStmt) {
+        declare(stmt.name)
+        define(stmt.name)
+    }
+
     override fun visitExpression(stmt: Expression) {
         resolve(stmt.expression)
     }

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

@@ -5,6 +5,7 @@ package fr.celticinfo.lox
  */
 interface StmtVisitor<R> {
     fun visitBlock(stmt: Block): R
+    fun visitClassStmt(stmt: ClassStmt): R
     fun visitExpression(stmt: Expression): R
     fun visitFunction(stmt: Function): R
     fun visitIf(stmt: If): R
@@ -29,6 +30,15 @@ data class Block(
     }
 }
 
+data class ClassStmt(
+    val name: Token,
+    val methods: List<Function>
+) : Stmt() {
+    override fun <R> accept(visitor: StmtVisitor<R>): R {
+        return visitor.visitClassStmt(this)
+    }
+}
+
 data class Expression(
     val expression: Expr
 ) : Stmt() {

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

@@ -769,4 +769,40 @@ var a = "global";
             System.setOut(standardOut)
         }
     }
+
+    @Test
+    fun `valid code with class declaration`() {
+        val standardOut = System.out
+        val outputStreamCaptor = ByteArrayOutputStream()
+
+        System.setOut(PrintStream(outputStreamCaptor))
+
+        try {
+            val code = """
+                class DevonshireCream {
+                  serveOn() {
+                    return "Scones";
+                  }
+                }
+                
+                print DevonshireCream;
+            """.trimIndent()
+            val scanner = Scanner(code)
+            val tokens = scanner.scanTokens()
+            val parser = Parser(tokens)
+            val statements = parser.parse()
+            assertEquals(2, statements.size)
+
+            val interpreter = Interpreter()
+
+            val resolver = Resolver(interpreter)
+            resolver.resolve(statements)
+
+            interpreter.interpret(statements)
+            val output = outputStreamCaptor.toString().trim()
+            assertEquals("DevonshireCream", output)
+        } finally {
+            System.setOut(standardOut)
+        }
+    }
 }

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

@@ -234,4 +234,24 @@ class ParserTest {
         val printStmt = stmt as Print
         assertTrue(printStmt.expression is Call)
     }
+
+    @Test
+    fun `valid code with class declaration`() {
+        val code = """
+            class DevonshireCream {
+              serveOn() {
+                return "Scones";
+              }
+            }
+            
+            print DevonshireCream;
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(2,statements.size)
+        val stmt = statements[0]
+        assertTrue(stmt is ClassStmt)
+    }
 }