Evaluate `return` Statement

3 files changed, 65 insertions, 7 deletions

diff --git a/evaluator/evaluator.go b/evaluator/evaluator.go
index 7aeaa24..3a9e54a 100644
--- a/evaluator/evaluator.go
+++ b/evaluator/evaluator.go
@@ -16,13 +16,13 @@ func Eval(node ast.Node) object.Object {
 	switch node := node.(type) {
 	// 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)
 
 	// Expressions
 	case *ast.IntegerLiteral:
@@ -42,16 +42,38 @@ func Eval(node ast.Node) object.Object {
 
 	case *ast.IfExpression:
 		return evalIfExpression(node)
+
+	case *ast.ReturnStatement:
+		val := Eval(node.ReturnValue)
+		return &object.ReturnValue{Value: val}
 	}
 
 	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
diff --git a/evaluator/evaluator_test.go b/evaluator/evaluator_test.go
index b124144..ca7738f 100644
--- a/evaluator/evaluator_test.go
+++ b/evaluator/evaluator_test.go
@@ -112,6 +112,31 @@ func TestIfElseExpressions(t *testing.T) {
 	}
 }
 
+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 {
+		evaulated := testEval(tt.input)
+		testIntegerObject(t, evaulated, tt.expected)
+	}
+}
+
 func testEval(input string) object.Object {
 	l := lexer.New(input)
 	p := parser.New(l)
diff --git a/object/object.go b/object/object.go
index cac36ac..fbecf88 100644
--- a/object/object.go
+++ b/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 {
@@ -25,6 +26,10 @@ type Boolean struct {
 
 type Null struct{}
 
+type ReturnValue struct {
+	Value Object
+}
+
 func (i *Integer) Type() ObjectType {
 	return INTEGER_OBJ
 }
@@ -49,4 +54,10 @@ func (n *Null) Inspect() string {
 	return "null"
 }
 
+func (rv *ReturnValue) Type() ObjectType {
+	return RETURN_VALUE_OBJ
+}
 
+func (rv *ReturnValue) Inspect() string {
+	return rv.Value.Inspect()
+}