Add Tokeniser::eat_if method

This method is used for consuming a multi-character sequence only if
that sequence matches a passed string.

1 files changed, 20 insertions, 0 deletions

diff --git a/src/tokeniser.rs b/src/tokeniser.rs
index 2214f42..3608e9e 100644
--- a/src/tokeniser.rs
+++ b/src/tokeniser.rs
@@ -93,6 +93,26 @@ impl Tokeniser {
         return option;
     }
 
+    /// Consume next characters if they match a pattern.
+    pub fn eat_if(&mut self, pattern: &str) -> Option<String> {
+        // Check that next characters match the pattern.
+        for (i, c) in pattern.chars().enumerate() {
+            if let Some(d) = self.chars.get(self.mark.i + i) {
+                if c == *d {
+                    continue;
+                }
+            }
+            return None;
+        }
+        // Consume the next characters.
+        self.prev = self.mark;
+        for c in pattern.chars() {
+            self.mark.advance(c);
+            self.mark_end();
+        }
+        return Some(pattern.to_string());
+    }
+
     /// Consume whitespace.
     pub fn eat_whitespace(&mut self) {
         while let Some(c) = self.peek_char() {