Merge pull request #6 from kamilturek/object-system-foundation

Object system & evaluator foundation

evaluator/evaluator.go

@@ -0,0 +1,93 @@
+package evaluator
+
+import (
+	"github.com/kamilturek/monkey/ast"
+	"github.com/kamilturek/monkey/object"
+)
+
+var (
+	NULL  = &object.Null{}
+	TRUE  = &object.Boolean{Value: true}
+	FALSE = &object.Boolean{Value: false}
+)
+
+func Eval(node ast.Node) object.Object {
+	switch node := node.(type) {
+	// Statements
+	case *ast.Program:
+		return evalStatements(node.Statements)
+	case *ast.ExpressionStatement:
+		return Eval(node.Expression)
+
+	// Expressions
+	case *ast.IntegerLiteral:
+		return &object.Integer{
+			Value: node.Value,
+		}
+	case *ast.BooleanLiteral:
+		return nativeBoolToBooleanObject(node.Value)
+	case *ast.PrefixExpression:
+		right := Eval(node.Right)
+
+		return evalPrefixExpression(node.Operator, right)
+	}
+
+	return nil
+}
+
+func evalStatements(stmts []ast.Statement) object.Object {
+	var result object.Object
+
+	for _, stmt := range stmts {
+		result = Eval(stmt)
+	}
+
+	return result
+}
+
+func evalPrefixExpression(operator string, right object.Object) object.Object {
+	switch operator {
+	case "!":
+		return evalBangOperatorExpression(right)
+	case "-":
+		return evalMinusPrefixOperatorExpression(right)
+	default:
+		return NULL
+	}
+}
+
+func evalBangOperatorExpression(right object.Object) object.Object {
+	switch right {
+	case TRUE:
+		return FALSE
+	case FALSE:
+		return TRUE
+	case NULL:
+		return TRUE
+	default:
+		return FALSE
+	}
+}
+
+func evalMinusPrefixOperatorExpression(right object.Object) object.Object {
+	if right.Type() != object.INTEGER_OBJ {
+		return NULL
+	}
+
+	integer, ok := right.(*object.Integer)
+	if !ok {
+		return NULL
+	}
+
+	return &object.Integer{
+		Value: -integer.Value,
+	}
+}
+
+func nativeBoolToBooleanObject(input bool) *object.Boolean {
+	if input {
+		return TRUE
+	}
+
+	return FALSE
+}

evaluator/evaluator_test.go

@@ -0,0 +1,113 @@
+package evaluator_test
+
+import (
+	"testing"
+
+	"github.com/kamilturek/monkey/evaluator"
+	"github.com/kamilturek/monkey/lexer"
+	"github.com/kamilturek/monkey/object"
+	"github.com/kamilturek/monkey/parser"
+)
+
+func testEval(input string) object.Object {
+	l := lexer.NewLexer(input)
+	p := parser.NewParser(l)
+	program := p.ParseProgram()
+
+	return evaluator.Eval(program)
+}
+
+func testIntegerObject(t *testing.T, obj object.Object, expected int64) bool {
+	t.Helper()
+
+	result, ok := obj.(*object.Integer)
+	if !ok {
+		t.Errorf("object is not Integer. got=%T (%+v)", obj, obj)
+
+		return false
+	}
+
+	if result.Value != expected {
+		t.Errorf("object has wrong value. got=%d, want=%d", expected, result.Value)
+
+		return false
+	}
+
+	return true
+}
+
+func testBooleanObject(t *testing.T, obj object.Object, expected bool) bool { //nolint:unparam
+	t.Helper()
+
+	result, ok := obj.(*object.Boolean)
+	if !ok {
+		t.Errorf("object is not Boolean. got=%T (%+v)", obj, obj)
+
+		return false
+	}
+
+	if result.Value != expected {
+		t.Errorf("object has wrong value. got=%t, want=%t", expected, result.Value)
+
+		return false
+	}
+
+	return true
+}
+
+func TestEvalIntegerExpression(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		input    string
+		expected int64
+	}{
+		{"5", 5},
+		{"10", 10},
+		{"-5", -5},
+		{"-10", -10},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testIntegerObject(t, evaluated, tt.expected)
+	}
+}
+
+func TestEvalBooleanExpression(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		input    string
+		expected bool
+	}{
+		{"true", true},
+		{"false", false},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testBooleanObject(t, evaluated, tt.expected)
+	}
+}
+
+func TestBangOperator(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		input    string
+		expected bool
+	}{
+		{"!true", false},
+		{"!false", true},
+		{"!5", false},
+		{"!!true", true},
+		{"!!false", false},
+		{"!!5", true},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testBooleanObject(t, evaluated, tt.expected)
+	}
+}

object/object.go

@@ -0,0 +1,58 @@
+package object
+
+import (
+	"strconv"
+)
+
+type ObjectType string
+
+const (
+	BOOLEAN_OBJ = "BOOLEAN"
+	INTEGER_OBJ = "INTEGER"
+	NULL_OBJ    = "NULL"
+)
+
+type Object interface {
+	Type() ObjectType
+	Inspect() string
+}
+
+// Integer
+
+type Integer struct {
+	Value int64
+}
+
+func (i *Integer) Type() ObjectType {
+	return INTEGER_OBJ
+}
+
+func (i *Integer) Inspect() string {
+	return strconv.FormatInt(i.Value, 10)
+}
+
+// Boolean
+
+type Boolean struct {
+	Value bool
+}
+
+func (b *Boolean) Type() ObjectType {
+	return BOOLEAN_OBJ
+}
+
+func (b *Boolean) Inspect() string {
+	return strconv.FormatBool(b.Value)
+}
+
+// Null
+
+type Null struct{}
+
+func (n *Null) Type() ObjectType {
+	return NULL_OBJ
+}
+
+func (n *Null) Inspect() string {
+	return "null"
+}

repl/repl.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 
+	"github.com/kamilturek/monkey/evaluator"
 	"github.com/kamilturek/monkey/lexer"
 	"github.com/kamilturek/monkey/parser"
 )
@@ -33,7 +34,10 @@ func Start(in io.Reader, out io.Writer) {
 			continue
 		}
 
-		fmt.Fprint(out, program.String(), "\n")
+		evaluated := evaluator.Eval(program)
+		if evaluated != nil {
+			fmt.Fprintf(out, "%s\n", evaluated.Inspect())
+		}
 	}
 }