Add function objects

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

@@ -3,7 +3,7 @@ package fr.celticinfo.lox
 import fr.celticinfo.lox.TokenType.*
 
 class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
-    private var globals = Environment()
+    var globals = Environment()
     private var environment = globals
 
     constructor() {
@@ -41,7 +41,7 @@ class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
         executeBlock(stmt.statements, Environment(environment))
     }
 
-    private fun executeBlock(statements: List<Stmt?>, environment: Environment) {
+    fun executeBlock(statements: List<Stmt?>, environment: Environment) {
         val previous = this.environment
         try {
             this.environment = environment
@@ -61,6 +61,11 @@ class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
         evaluate(stmt.expression)
     }
 
+    override fun visitFunction(stmt: Function) {
+        val function = LoxFunction(stmt)
+        environment.define(stmt.name.lexeme, function)
+    }
+
     override fun visitIf(stmt: If) {
         if (isTruthy(evaluate(stmt.condition))) {
             execute(stmt.thenBranch)

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

@@ -0,0 +1,27 @@
+package fr.celticinfo.lox
+
+class LoxFunction : LoxCallable {
+    private val declaration: Function
+
+    constructor(declaration: Function) {
+        this.declaration = declaration
+    }
+
+    override fun call(interpreter: Interpreter, arguments: List<Any?>): Any? {
+        val environment = Environment(interpreter.globals)
+        for (i in declaration.params.indices) {
+            environment.define(declaration.params[i].lexeme, arguments[i])
+        }
+        interpreter.executeBlock(declaration.body, environment)
+        return null
+    }
+
+    override fun arity(): Int {
+        return declaration.params.size
+    }
+
+    override fun toString(): String {
+        return "<fn ${declaration.name.lexeme}>"
+    }
+
+}

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

@@ -387,4 +387,32 @@ print clock();
         }
     }
 
+    @Test
+    fun `Function should work`() {
+        val standardOut = System.out
+        val outputStreamCaptor = ByteArrayOutputStream()
+
+        System.setOut(PrintStream(outputStreamCaptor))
+
+        try {
+            val code = """
+fun sayHi(first, last) {
+  print "Hi, " + first + " " + last + "!";
+}
+
+sayHi("Dear", "Reader");
+ """
+            val scanner = Scanner(code)
+            val tokens = scanner.scanTokens()
+            val parser = Parser(tokens)
+            val statements = parser.parse()
+            assertEquals(2, statements.size)
+
+            Interpreter().interpret(statements)
+            val output = outputStreamCaptor.toString().trim()
+            assertEquals("Hi, Dear Reader!", output)
+        } finally {
+            System.setOut(standardOut)
+        }
+    }
 }