bind expression (:=) instead of let

lexer/lexer.go

@@ -134,7 +134,14 @@ func (l *Lexer) NextToken() token.Token {
 	case ']':
 		tok = newToken(token.RBRACKET, l.ch)
 	case ':':
-		tok = newToken(token.COLON, l.ch)
+		if l.peekChar() == '=' {
+			ch := l.ch
+			l.readChar()
+			literal := string(ch) + string(l.ch)
+			tok = token.Token{Type: token.BIND, Literal: literal}
+		} else {
+			tok = newToken(token.COLON, l.ch)
+		}
 	default:
 		if isLetter(l.ch) {
 			tok.Literal = l.readIdentifier()

lexer/lexer_test.go

@@ -7,15 +7,15 @@ import (
 
 func TestNextToken(t *testing.T) {
 	input := `#!./monkey-lang
-				let five = 5;
-				let ten = 10;
+				five := 5;
+				ten := 10;
 				
-				let add = fn(x, y) {
+				add := fn(x, y) {
 				  x + y;
 				};
 				
 				# this is a comment
-				let result = add(five, ten);
+				result := add(five, ten);
 				!-/*5;
 				5 < 10 > 5;
 				
@@ -40,19 +40,16 @@ func TestNextToken(t *testing.T) {
 		expectedLiteral string
 	}{
 		{token.COMMENT, "!./monkey-lang"},
-		{token.LET, "let"},
 		{token.IDENT, "five"},
-		{token.ASSIGN, "="},
+		{token.BIND, ":="},
 		{token.INT, "5"},
 		{token.SEMICOLON, ";"},
-		{token.LET, "let"},
 		{token.IDENT, "ten"},
-		{token.ASSIGN, "="},
+		{token.BIND, ":="},
 		{token.INT, "10"},
 		{token.SEMICOLON, ";"},
-		{token.LET, "let"},
 		{token.IDENT, "add"},
-		{token.ASSIGN, "="},
+		{token.BIND, ":="},
 		{token.FUNCTION, "fn"},
 		{token.LPAREN, "("},
 		{token.IDENT, "x"},
@@ -67,9 +64,8 @@ func TestNextToken(t *testing.T) {
 		{token.RBRACE, "}"},
 		{token.SEMICOLON, ";"},
 		{token.COMMENT, " this is a comment"},
-		{token.LET, "let"},
 		{token.IDENT, "result"},
-		{token.ASSIGN, "="},
+		{token.BIND, ":="},
 		{token.IDENT, "add"},
 		{token.LPAREN, "("},
 		{token.IDENT, "five"},
@@ -163,9 +159,9 @@ func TestNextToken(t *testing.T) {
 
 func TestStringEscapes(t *testing.T) {
 	input := `#!./monkey-lang
-let a = "\"foo\""
-let b = "\x00\x0a\x7f"
-let c = "\r\n\t"
+a := "\"foo\""
+b := "\x00\x0a\x7f"
+c := "\r\n\t"
 `
 
 	tests := []struct {
@@ -173,17 +169,14 @@ let c = "\r\n\t"
 		expectedLiteral string
 	}{
 		{token.COMMENT, "!./monkey-lang"},
-		{token.LET, "let"},
 		{token.IDENT, "a"},
-		{token.ASSIGN, "="},
+		{token.BIND, ":="},
 		{token.STRING, "\"foo\""},
-		{token.LET, "let"},
 		{token.IDENT, "b"},
-		{token.ASSIGN, "="},
+		{token.BIND, ":="},
 		{token.STRING, "\x00\n\u007f"},
-		{token.LET, "let"},
 		{token.IDENT, "c"},
-		{token.ASSIGN, "="},
+		{token.BIND, ":="},
 		{token.STRING, "\r\n\t"},
 		{token.EOF, ""},
 	}