Add support for [this]

src/main/ExprGenerator.ws.kts

@@ -48,6 +48,7 @@ val exprTypes = listOf(
     "Literal  : Any? value",
     "Logical  : Expr left, Token operator, Expr right",
     "Set      : Expr obj, Token name, Expr value",
+    "This     : Token keyword",
     "Unary    : Token operator, Expr right",
     "Variable : Token name"
 )

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

@@ -37,6 +37,10 @@ class AstPrinter : ExprVisitor<String> {
         return parenthesize("set", expr.obj, Literal(expr.name), expr.value)
     }
 
+    override fun visitThis(expr: This): String {
+        return "this"
+    }
+
     override fun visitUnary(expr: Unary): String {
         return parenthesize(expr.operator.lexeme, expr.right)
     }

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

@@ -12,6 +12,7 @@ interface ExprVisitor<R> {
     fun visitLiteral(expr: Literal): R
     fun visitLogical(expr: Logical): R
     fun visitSet(expr: Set): R
+    fun visitThis(expr: This): R
     fun visitUnary(expr: Unary): R
     fun visitVariable(expr: Variable): R
 }
@@ -95,6 +96,14 @@ data class Set(
     }
 }
 
+data class This(
+    val keyword: Token
+) : Expr() {
+    override fun <R> accept(visitor: ExprVisitor<R>): R {
+        return visitor.visitThis(this)
+    }
+}
+
 data class Unary(
     val operator: Token, val right: Expr
 ) : Expr() {

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

@@ -211,6 +211,10 @@ class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
         return value
     }
 
+    override fun visitThis(expr: This): Any? {
+        return lookUpVariable(expr.keyword, expr)
+    }
+
     override fun visitUnary(expr: Unary): Any? {
         val right = evaluate(expr.right)
 

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

@@ -5,6 +5,12 @@ class LoxFunction(
     private val closure: Environment
 ) : LoxCallable {
 
+    fun bind(instance: LoxInstance): LoxFunction {
+        val environment = Environment(closure)
+        environment.define("this", instance)
+        return LoxFunction(declaration, environment)
+    }
+
     override fun call(interpreter: Interpreter, arguments: List<Any?>): Any? {
         val environment = Environment(closure)
 

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

@@ -10,7 +10,7 @@ class LoxInstance(private val klass: LoxClass) {
 
         val method = klass.findMethod(name.lexeme)
         if (method != null) {
-            return method
+            return method.bind(this)
         }
 
         throw RuntimeError(name, "Undefined property '${name.lexeme}'.")

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

@@ -336,6 +336,7 @@ 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(THIS) -> return This(previous())
             match(IDENTIFIER) -> return Variable(previous())
             match(LEFT_PAREN) -> {
                 val expr = expression()

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

@@ -6,6 +6,8 @@ package fr.celticinfo.lox
 class Resolver(private val interpreter: Interpreter) : ExprVisitor<Unit>, StmtVisitor<Unit> {
     private val scopes = mutableListOf<MutableMap<String, Boolean>>()
     private var currentFunctionType = FunctionType.NONE
+    private var currentClassType = ClassType.NONE
+
 
     init {
         scopes.add(mutableMapOf())
@@ -18,13 +20,22 @@ class Resolver(private val interpreter: Interpreter) : ExprVisitor<Unit>, StmtVi
     }
 
     override fun visitClassStmt(stmt: ClassStmt) {
+        val enclosingClassType = currentClassType
+        currentClassType = ClassType.CLASS
+
         declare(stmt.name)
         define(stmt.name)
 
+        beginScope()
+        scopes.last()["this"] = true
+
         for (method in stmt.methods) {
             val declaration = FunctionType.METHOD
             resolveFunction(method, declaration)
         }
+        endScope()
+
+        currentClassType = enclosingClassType
     }
 
     override fun visitExpression(stmt: Expression) {
@@ -110,6 +121,14 @@ class Resolver(private val interpreter: Interpreter) : ExprVisitor<Unit>, StmtVi
         resolve(expr.obj)
     }
 
+    override fun visitThis(expr: This) {
+        if (currentClassType == ClassType.NONE) {
+            Lox.error(expr.keyword, "Cannot use 'this' outside of a class.")
+            return
+        }
+        resolveLocal(expr, expr.keyword)
+    }
+
     override fun visitUnary(expr: Unary) {
         resolve(expr.right)
     }
@@ -180,3 +199,8 @@ enum class FunctionType {
     FUNCTION,
     METHOD
 }
+
+enum class ClassType {
+    NONE,
+    CLASS
+}

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

@@ -39,6 +39,10 @@ class RpnPrinter : ExprVisitor<String> {
         return stack("set", expr.obj, Literal(expr.name), expr.value)
     }
 
+    override fun visitThis(expr: This): String {
+        return "this"
+    }
+
     override fun visitUnary(expr: Unary): String {
         return stack(expr.operator.lexeme, expr.right)
     }

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

@@ -907,4 +907,44 @@ var a = "global";
         } finally {
             System.setOut(standardOut)
         }
-    }}
+    }
+
+    @Test
+    fun `valid code with this`() {
+        val standardOut = System.out
+        val outputStreamCaptor = ByteArrayOutputStream()
+
+        System.setOut(PrintStream(outputStreamCaptor))
+
+        try {
+            val code = """
+                class Cake {
+                  taste() {
+                    var adjective = "delicious";
+                    print "The " + this.flavor + " cake is " + adjective + "!";
+                  }
+                }
+                
+                var cake = Cake();
+                cake.flavor = "German chocolate";
+                cake.taste();
+            """.trimIndent()
+            val scanner = Scanner(code)
+            val tokens = scanner.scanTokens()
+            val parser = Parser(tokens)
+            val statements = parser.parse()
+            assertEquals(4, statements.size)
+
+            val interpreter = Interpreter()
+
+            val resolver = Resolver(interpreter)
+            resolver.resolve(statements)
+
+            interpreter.interpret(statements)
+            val output = outputStreamCaptor.toString().trim()
+            assertEquals("The German chocolate cake is delicious!", output)
+        } finally {
+            System.setOut(standardOut)
+        }
+    }
+}

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

@@ -311,4 +311,29 @@ class ParserTest {
         assertTrue(statements[0] is ClassStmt)
         assertTrue(statements[1] is Expression)
     }
+
+    @Test
+    fun `valid code with this`() {
+        val code = """
+            class Cake {
+              taste() {
+                var adjective = "delicious";
+                print "The " + this.flavor + " cake is " + adjective + "!";
+              }
+            }
+            
+            var cake = Cake();
+            cake.flavor = "German chocolate";
+            cake.taste();
+        """.trimIndent()
+        val scanner = Scanner(code)
+        val tokens = scanner.scanTokens()
+        val parser = Parser(tokens)
+        val statements = parser.parse()
+        assertEquals(4,statements.size)
+        assertTrue(statements[0] is ClassStmt)
+        assertTrue(statements[1] is Var)
+        assertTrue(statements[2] is Expression)
+        assertTrue(statements[3] is Expression)
+    }
 }