1 files changed, 91 insertions, 0 deletions

diff --git a/crates/ra_mbe/src/tt_cursor.rs b/crates/ra_mbe/src/tt_cursor.rs
new file mode 100644
index 000000000..30c8eda67
--- /dev/null
+++ b/crates/ra_mbe/src/tt_cursor.rs
@@ -0,0 +1,91 @@
+#[derive(Clone)]
+pub(crate) struct TtCursor<'a> {
+    subtree: &'a tt::Subtree,
+    pos: usize,
+}
+
+impl<'a> TtCursor<'a> {
+    pub(crate) fn new(subtree: &'a tt::Subtree) -> TtCursor<'a> {
+        TtCursor { subtree, pos: 0 }
+    }
+
+    pub(crate) fn is_eof(&self) -> bool {
+        self.pos == self.subtree.token_trees.len()
+    }
+
+    pub(crate) fn current(&self) -> Option<&'a tt::TokenTree> {
+        self.subtree.token_trees.get(self.pos)
+    }
+
+    pub(crate) fn at_punct(&self) -> Option<&'a tt::Punct> {
+        match self.current() {
+            Some(tt::TokenTree::Leaf(tt::Leaf::Punct(it))) => Some(it),
+            _ => None,
+        }
+    }
+
+    pub(crate) fn at_char(&self, char: char) -> bool {
+        match self.at_punct() {
+            Some(tt::Punct { char: c, .. }) if *c == char => true,
+            _ => false,
+        }
+    }
+
+    pub(crate) fn at_ident(&mut self) -> Option<&'a tt::Ident> {
+        match self.current() {
+            Some(tt::TokenTree::Leaf(tt::Leaf::Ident(i))) => Some(i),
+            _ => None,
+        }
+    }
+
+    pub(crate) fn bump(&mut self) {
+        self.pos += 1;
+    }
+    pub(crate) fn rev_bump(&mut self) {
+        self.pos -= 1;
+    }
+
+    pub(crate) fn eat(&mut self) -> Option<&'a tt::TokenTree> {
+        match self.current() {
+            Some(it) => {
+                self.bump();
+                Some(it)
+            }
+            None => None,
+        }
+    }
+
+    pub(crate) fn eat_subtree(&mut self) -> Option<&'a tt::Subtree> {
+        match self.current()? {
+            tt::TokenTree::Subtree(sub) => {
+                self.bump();
+                Some(sub)
+            }
+            _ => return None,
+        }
+    }
+
+    pub(crate) fn eat_punct(&mut self) -> Option<&'a tt::Punct> {
+        if let Some(it) = self.at_punct() {
+            self.bump();
+            return Some(it);
+        }
+        None
+    }
+
+    pub(crate) fn eat_ident(&mut self) -> Option<&'a tt::Ident> {
+        if let Some(i) = self.at_ident() {
+            self.bump();
+            return Some(i);
+        }
+        None
+    }
+
+    pub(crate) fn expect_char(&mut self, char: char) -> Option<()> {
+        if self.at_char(char) {
+            self.bump();
+            return Some(());
+        }
+        None
+    }
+}