string literal!!

ast/ast.go

@@ -236,3 +236,12 @@ func (ce *CallExpression) String() string {
 	out.WriteString(")")
 	return out.String()
 }
+
+type StringLiteral struct {
+	Token token.Token
+	Value string
+}
+
+func (sl *StringLiteral) expressionNode()      {}
+func (sl *StringLiteral) TokenLiteral() string { return sl.Token.Literal }
+func (sl *StringLiteral) String() string       { return sl.Token.Literal }

evaluator/evaluator.go

@@ -71,6 +71,8 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 			return args[0]
 		}
 		return applyFunction(function, args)
+	case *ast.StringLiteral:
+		return &object.String{Value: node.Value}
 	}
 	return nil
 }

lexer/lexer.go

@@ -84,6 +84,9 @@ func (l *Lexer) NextToken() token.Token {
 		tok = newToken(token.LBRACE, l.ch)
 	case '}':
 		tok = newToken(token.RBRACE, l.ch)
+	case '"':
+		tok.Type = token.STRING
+		tok.Literal = l.readString()
 	case 0:
 		tok.Literal = ""
 		tok.Type = token.EOF
@@ -137,6 +140,17 @@ func (l *Lexer) readNumber() string {
 	return l.input[position:l.position]
 }
 
+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]
+}
+
 func isDigit(ch byte) bool {
 	return '0' <= ch && ch <= '9'
 }

object/object.go

@@ -16,11 +16,14 @@ type Object interface {
 }
 
 const (
-	INTEGER_OBJ      = "INTEGER"
-	BOOLEAN_OBJ      = "BOOLEAN"
-	NULL_OBJ         = "NULL"
+	INTEGER_OBJ = "INTEGER"
+	STRING_OBJ  = "STRING"
+	BOOLEAN_OBJ = "BOOLEAN"
+
+	NULL_OBJ  = "NULL"
+	ERROR_OBJ = "ERROR"
+
 	RETURN_VALUE_OBJ = "RETURN_VALUE"
-	ERROR_OBJ        = "ERROR"
 	FUNCTION_OBJ     = "FUNCTION"
 )
 
@@ -78,3 +81,10 @@ type Error struct {
 
 func (e *Error) Type() ObjectType { return ERROR_OBJ }
 func (e *Error) Inspect() string  { return "ERROR: " + e.Message }
+
+type String struct {
+	Value string
+}
+
+func (s *String) Type() ObjectType { return STRING_OBJ }
+func (s *String) Inspect() string  { return s.Value }

parser/parser.go

@@ -60,6 +60,8 @@ func New(l *lexer.Lexer) *Parser {
 	p.prefixParseFns = make(map[token.TokenType]prefixParseFn)
 	p.registerPrefix(token.IDENTIFIER, p.parseIdentifier)
 	p.registerPrefix(token.INT, p.parseIntegerLiteral)
+	p.registerPrefix(token.STRING, p.parseStringLiteral)
+
 	p.registerPrefix(token.BANG, p.parsePrefixExpression)
 	p.registerPrefix(token.MINUS, p.parsePrefixExpression)
 	p.registerPrefix(token.TRUE, p.parseBoolean)
@@ -104,6 +106,10 @@ func (p *Parser) curPrecedence() int {
 	return LOWEST
 }
 
+func (p *Parser) parseStringLiteral() ast.Expression {
+	return &ast.StringLiteral{Token: p.curToken, Value: p.curToken.Literal}
+}
+
 func (p *Parser) parseCallExpression(function ast.Expression) ast.Expression {
 	exp := &ast.CallExpression{Token: p.curToken, Function: function}
 	exp.Arguments = p.parseCallArguments()
@@ -202,9 +208,7 @@ func (p *Parser) parseBlockStatement() *ast.BlockStatement {
 	p.nextToken()
 	for !p.curTokenIs(token.RBRACE) && !p.curTokenIs(token.EOF) {
 		stmt := p.parseStatement()
-		if stmt != nil {
-			block.Statements = append(block.Statements, stmt)
-		}
+		block.Statements = append(block.Statements, stmt)
 		p.nextToken()
 	}
 	return block
@@ -290,9 +294,7 @@ func (p *Parser) ParseProgram() *ast.Program {
 
 	for p.curToken.Type != token.EOF {
 		stmt := p.parseStatement()
-		if stmt != nil {
-			program.Statements = append(program.Statements, stmt)
-		}
+		program.Statements = append(program.Statements, stmt)
 		p.nextToken()
 	}