comments

lexer/lexer.go

@@ -7,6 +7,7 @@ type Lexer struct {
 	position     int  // current position in input (point to current char)
 	readPosition int  // current reading position in input (after current char)
 	ch           byte // current char under exclamation
+	prevCh       byte // previous char read
 }
 
 func New(input string) *Lexer {
@@ -16,6 +17,7 @@ func New(input string) *Lexer {
 }
 
 func (l *Lexer) readChar() {
+	l.prevCh = l.ch
 	if l.readPosition >= len(l.input) {
 		l.ch = 0
 	} else {
@@ -39,6 +41,9 @@ func (l *Lexer) NextToken() token.Token {
 	l.skipWhitespace()
 
 	switch l.ch {
+	case '#':
+		tok.Type = token.COMMENT
+		tok.Literal = l.readLine()
 	case '=':
 		if l.peekChar() == '=' {
 			ch := l.ch
@@ -69,7 +74,13 @@ func (l *Lexer) NextToken() token.Token {
 		}
 
 	case '/':
-		tok = newToken(token.SLASH, l.ch)
+		if l.peekChar() == '/' {
+			l.readChar()
+			tok.Type = token.COMMENT
+			tok.Literal = l.readLine()
+		} else {
+			tok = newToken(token.SLASH, l.ch)
+		}
 	case '*':
 		tok = newToken(token.ASTERISK, l.ch)
 	case '<':
@@ -165,3 +176,14 @@ func (l *Lexer) readString() string {
 	}
 	return l.input[position:l.position]
 }
+
+func (l *Lexer) readLine() string {
+	position := l.position + 1
+	for {
+		l.readChar()
+		if l.ch == '\r' || l.ch == '\n' || l.ch == 0 {
+			break
+		}
+	}
+	return l.input[position:l.position]
+}

lexer/lexer_test.go

@@ -6,13 +6,15 @@ import (
 )
 
 func TestNextToken(t *testing.T) {
-	input := `let five = 5;
+	input := `#!./monkey-lang
+				let five = 5;
 				let ten = 10;
 				
 				let add = fn(x, y) {
 				  x + y;
 				};
 				
+				# this is a comment
 				let result = add(five, ten);
 				!-/*5;
 				5 < 10 > 5;
@@ -23,6 +25,7 @@ func TestNextToken(t *testing.T) {
 					return false;
 				}
 				
+				// this is another comment
 				10 == 10;
 				10 != 9;
 				"foobar"
@@ -35,6 +38,7 @@ func TestNextToken(t *testing.T) {
 		expectedType    token.TokenType
 		expectedLiteral string
 	}{
+		{token.COMMENT, "!./monkey-lang"},
 		{token.LET, "let"},
 		{token.IDENT, "five"},
 		{token.ASSIGN, "="},
@@ -61,6 +65,7 @@ func TestNextToken(t *testing.T) {
 		{token.SEMICOLON, ";"},
 		{token.RBRACE, "}"},
 		{token.SEMICOLON, ";"},
+		{token.COMMENT, " this is a comment"},
 		{token.LET, "let"},
 		{token.IDENT, "result"},
 		{token.ASSIGN, "="},
@@ -106,7 +111,7 @@ func TestNextToken(t *testing.T) {
 		{token.SEMICOLON, ";"},
 
 		{token.RBRACE, "}"},
-
+		{token.COMMENT, " this is another comment"},
 		{token.INT, "10"},
 		{token.EQ, "=="},
 		{token.INT, "10"},