feat: add comment support

close #52

Author: gengjiawen

lexer/lexer_test.rs

@@ -35,6 +35,11 @@ mod tests {
         test_lexer_common("let", "let x=5");
     }
 
+    #[test]
+    fn test_comments() {
+        test_lexer_common("comments", "// I am comments");
+    }
+
     #[test]
     fn test_lexer_let_with_space() {
         test_lexer_common("let_with_space", "let x = 5");
@@ -62,7 +67,9 @@ mod tests {
 
     #[test]
     fn test_lexer_complex() {
-        test_lexer_common("complex", "let five = 5;
+        test_lexer_common("complex", "
+// welcome to monkeylang
+let five = 5;
 let ten = 10;
 
 let add = fn(x, y) {

lexer/lib.rs

@@ -53,6 +53,7 @@ impl<'a> Lexer<'a> {
     pub fn next_token(&mut self) -> Token {
         // println!("self ch {}, position {} read_position {}", self.ch, self.position, self.read_position);
         self.skip_whitespace();
+        self.skip_comments();
         let t = match self.ch {
             '=' => {
                 if self.peek_char() == '=' {
@@ -113,6 +114,23 @@ impl<'a> Lexer<'a> {
         }
     }
 
+    fn skip_comments(&mut self) {
+        if self.ch == '/' && self.peek_char() == '/' {
+            self.read_char();
+            self.read_char();
+            loop {
+                self.read_char();
+                if self.ch == '\n' || self.ch == '\u{0}' {
+                    // consume the comments end
+                    if self.ch == '\n' {
+                        self.read_char();
+                    }
+                    break
+                }
+            }
+        }
+    }
+
     fn read_identifier(&mut self) -> (usize, usize, String) {
         let pos = self.position;
         while is_letter(self.ch) {

lexer/snapshots/lexer__lexer_test__tests__comments.snap

@@ -0,0 +1,15 @@
+---
+source: lexer/lexer_test.rs
+expression: // I am comments
+---
+[
+  {
+    "kind": {
+      "type": "EOF"
+    },
+    "span": {
+      "start": 16,
+      "end": 17
+    }
+  }
+]