Strings

ast/ast.go

@@ -264,3 +264,16 @@ func (ce *CallExpression) String() string {
 
 	return out.String()
 }
+
+type StringLiteral struct {
+	Token token.Token
+	Value string
+}
+
+func (sl StringLiteral) TokenLiteral() string {
+	return sl.Token.Literal
+}
+func (sl StringLiteral) String() string {
+	return sl.Token.Literal
+}
+func (sl StringLiteral) expressionNode() {}

evaluator/evaluator.go

@@ -94,6 +94,9 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 
 		return applyFunction(function, args)
 
+	case *ast.StringLiteral:
+		return &object.String{Value: node.Value}
+
 	}
 
 	return nil
@@ -178,6 +181,8 @@ func evalInfixExpression(operator string, left, right object.Object) object.Obje
 	switch {
 	case left.Type() == object.INTEGER_OBJ && right.Type() == object.INTEGER_OBJ:
 		return evalIntegerInfixExpression(operator, left, right)
+	case left.Type() == object.STRING_OBJ && right.Type() == object.STRING_OBJ:
+		return evalStringInfixExpression(operator, left, right)
 	case operator == "==":
 		return nativeBoolToBooleanObject(left == right)
 	case operator == "!=":
@@ -189,6 +194,17 @@ func evalInfixExpression(operator string, left, right object.Object) object.Obje
 	}
 }
 
+func evalStringInfixExpression(operator string, left object.Object, right object.Object) object.Object {
+	if operator != "+" {
+		return newError("unknown operator: %s %s %s", left.Type(), operator, right.Type())
+	}
+
+	leftVal := left.(*object.String).Value
+	rightVal := right.(*object.String).Value
+
+	return &object.String{Value: leftVal + rightVal}
+}
+
 func evalIntegerInfixExpression(operator string, left, right object.Object) object.Object {
 	leftVal := left.(*object.Integer).Value
 	rightVal := right.(*object.Integer).Value

evaluator/evaluator_test.go

@@ -205,6 +205,10 @@ func TestErrorHandling(t *testing.T) {
 			"foobar",
 			"identifier not found: foobar",
 		},
+		{
+			`"Hello" - "World"`,
+			"unknown operator: STRING - STRING",
+		},
 	}
 
 	for _, tt := range tests {
@@ -294,6 +298,34 @@ func TestClosures(t *testing.T) {
 	testIntegerObject(t, testEval(input), 4)
 }
 
+func TestStringLiteral(t *testing.T) {
+	input := `"Hello World!"`
+
+	evaluated := testEval(input)
+	str, ok := evaluated.(*object.String)
+	if !ok {
+		t.Fatalf("object is not String. got=%T (+%v)", evaluated, evaluated)
+	}
+
+	if str.Value != "Hello World!" {
+		t.Errorf("String has wrong value. got=%q", str.Value)
+	}
+}
+
+func TestStringConcatenation(t *testing.T) {
+	input := `"Hello" + " " + "World!"`
+
+	evaluated := testEval(input)
+	str, ok := evaluated.(*object.String)
+	if !ok {
+		t.Fatalf("object is not String. got=%T (+%v)", evaluated, evaluated)
+	}
+
+	if str.Value != "Hello World!" {
+		t.Errorf("String has wrong value. got=%q", str.Value)
+	}
+}
+
 func testEval(input string) object.Object {
 	l := lexer.New(input)
 	p := parser.New(l)

lexer/lexer.go

@@ -91,6 +91,9 @@ func (l *Lexer) NextToken() token.Token {
 	case 0:
 		tok.Literal = ""
 		tok.Type = token.EOF
+	case '"':
+		tok.Type = token.STRING
+		tok.Literal = l.readString()
 	default:
 		if isLetter(l.ch) {
 			tok.Literal = l.readIdentifier()
@@ -145,3 +148,14 @@ func (l *Lexer) skipWhitespace() {
 		l.readChar()
 	}
 }
+
+func (l *Lexer) readString() string {
+	position := l.position + 1
+	for {
+		l.readChar()
+		if l.ch == '"' || l.ch == 0 {
+			break
+		}
+	}
+	return l.input[position:l.position]
+}

lexer/lexer_test.go

@@ -25,6 +25,8 @@ if (5 < 10) {
 				
 				10 == 10;
 				10 != 9;
+				"foobar"
+				"foo bar"
 			`
 
 	tests := []struct {
@@ -113,6 +115,8 @@ if (5 < 10) {
 		{token.INT, "9"},
 		{token.SEMICOLON, ";"},
 
+		{token.STRING, "foobar"},
+		{token.STRING, "foo bar"},
 		{token.EOF, ""},
 	}
 

object/object.go

@@ -16,6 +16,7 @@ const (
 	RETURN_VALUE_OBJ = "RETURN_VALUE"
 	ERROR_OBJ        = "ERROR"
 	FUNCTION_OBJ     = "FUNCTION"
+	STRING_OBJ       = "STRING"
 )
 
 type Object interface {
@@ -85,11 +86,11 @@ type Function struct {
 	Env        *Environment
 }
 
-func (f Function) Type() ObjectType {
+func (f *Function) Type() ObjectType {
 	return FUNCTION_OBJ
 }
 
-func (f Function) Inspect() string {
+func (f *Function) Inspect() string {
 	var out bytes.Buffer
 
 	params := []string{}
@@ -106,3 +107,15 @@ func (f Function) Inspect() string {
 
 	return out.String()
 }
+
+type String struct {
+	Value string
+}
+
+func (s *String) Type() ObjectType {
+	return STRING_OBJ
+}
+
+func (s *String) Inspect() string {
+	return s.Value
+}

parser/parser.go

@@ -64,6 +64,7 @@ func New(l *lexer.Lexer) *Parser {
 	p.registerPrefix(token.LPAREN, p.parseGroupedExpression)
 	p.registerPrefix(token.IF, p.parseIfExpression)
 	p.registerPrefix(token.FUNCTION, p.parseFunctionLiteral)
+	p.registerPrefix(token.STRING, p.parseStringLiteral)
 
 	p.infixParseFns = make(map[token.TokenType]infixParseFn)
 	p.registerInfix(token.PLUS, p.parseInfixExpression)
@@ -430,3 +431,7 @@ func (p *Parser) registerPrefix(tokenType token.TokenType, fn prefixParseFn) {
 func (p *Parser) registerInfix(tokenType token.TokenType, fn infixParseFn) {
 	p.infixParseFns[tokenType] = fn
 }
+
+func (p *Parser) parseStringLiteral() ast.Expression {
+	return &ast.StringLiteral{Token: p.curToken, Value: p.curToken.Literal}
+}

parser/parser_test.go

@@ -670,6 +670,25 @@ func TestCallExpressionParameterParsing(t *testing.T) {
 	}
 }
 
+func TestStringLiteralExpression(t *testing.T) {
+	input := `"hello world";`
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	stmt := program.Statements[0].(*ast.ExpressionStatement)
+	literal, ok := stmt.Expression.(*ast.StringLiteral)
+	if !ok {
+		t.Fatalf("exp not *ast.StringLiteral. got=%T", stmt.Expression)
+	}
+
+	if literal.Value != "hello world" {
+		t.Errorf("literal.Value not %q. got=%q", "hello world", literal.Value)
+	}
+}
+
 func testLetStatement(t *testing.T, s ast.Statement, name string) bool {
 	if s.TokenLiteral() != "let" {
 		t.Errorf("s.TokenLiteral not 'let'. got=%q", s.TokenLiteral())

token/token.go

@@ -14,6 +14,7 @@ const (
 	// Identifiers + literals
 	IDENT  = "IDENT" // add, foobar, x, y
 	INT    = "INT"   // 123456
+	STRING = "STRING"
 
 	// Operators
 	ASSIGN   = "="