3.7: Evaluate return statements

evaluator/evaluator.go

@@ -16,11 +16,14 @@ func Eval(node ast.Node) object.Object {
 
 	// statements
 	case *ast.Program:
-		return evalStatements(node.Statements)
+		return evalProgram(node)
 	case *ast.ExpressionStatement:
 		return Eval(node.Expression)
 	case *ast.BlockStatement:
-		return evalStatements(node.Statements)
+		return evalBlockStatement(node)
+	case *ast.ReturnStatement:
+		val := Eval(node.ReturnValue)
+		return &object.ReturnValue{Value: val}
 
 	// expressions
 	case *ast.IntegerLiteral:
@@ -42,11 +45,29 @@ func Eval(node ast.Node) object.Object {
 	return nil
 }
 
-func evalStatements(stmts []ast.Statement) object.Object {
+func evalProgram(program *ast.Program) object.Object {
 	var result object.Object
 
-	for _, statement := range stmts {
+	for _, statement := range program.Statements {
 		result = Eval(statement)
+
+		if returnValue, ok := result.(*object.ReturnValue); ok {
+			return returnValue.Value
+		}
+	}
+
+	return result
+}
+
+func evalBlockStatement(block *ast.BlockStatement) object.Object {
+	var result object.Object
+
+	for _, statement := range block.Statements {
+		result = Eval(statement)
+
+		if result != nil && result.Type() == object.RETURN_VALUE_OBJ {
+			return result
+		}
 	}
 
 	return result

evaluator/evaluator_test.go

@@ -155,3 +155,30 @@ func testNullObject(t *testing.T, obj object.Object) bool {
 	}
 	return true
 }
+
+func TestReturnStatements(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected int64
+	}{
+		{"return 10;", 10},
+		{"return 10; 9;", 10},
+		{"return 2 * 5; 9;", 10},
+		{"9; return 2 * 5; 9;", 10},
+		{`
+if (10 > 1) {
+  if (10 > 1) {
+    return 10;
+  }
+
+  return 1;
+}
+`, 10,
+		},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testIntegerObject(t, evaluated, tt.expected)
+	}
+}

object/object.go

@@ -5,9 +5,10 @@ import "fmt"
 type ObjectType string
 
 const (
-	INTEGER_OBJ = "INTEGER"
-	BOOLEAN_OBJ = "BOOLEAN"
-	NULL_OBJ    = "NULL"
+	INTEGER_OBJ      = "INTEGER"
+	BOOLEAN_OBJ      = "BOOLEAN"
+	NULL_OBJ         = "NULL"
+	RETURN_VALUE_OBJ = "RETURN_VALUE"
 )
 
 type Object interface {
@@ -33,3 +34,10 @@ type Null struct{}
 
 func (n *Null) Type() ObjectType { return NULL_OBJ }
 func (n *Null) Inspect() string  { return "null" }
+
+type ReturnValue struct {
+	Value Object
+}
+
+func (rv *ReturnValue) Type() ObjectType { return RETURN_VALUE_OBJ }
+func (rv *ReturnValue) Inspect() string  { return rv.Value.Inspect() }