diff --git a/crates/lexer/src/lib.rs b/crates/lexer/src/lib.rs
index b422eb9..4ca2263 100644
--- a/crates/lexer/src/lib.rs
+++ b/crates/lexer/src/lib.rs
@@ -445,120 +445,80 @@ impl LexemeParser {
     }
 }
 
-// but what if...? prefix-tree!
-mod trie {
-    use super::Token;
-    use std::collections::BTreeMap;
+use trie::{OnceAndIter, Tree};
 
-    #[derive(Debug, Default)]
-    struct Node {
-        keys: Vec<char>,
-        values: Vec<Option<Token>>,
-        edges: Vec<Option<Box<Node>>>,
-    }
+pub struct LexemeIterator<I: Iterator<Item = char>> {
+    trie: Tree<char, Token>,
+    iter: OnceAndIter<I, char>,
+}
 
-    #[derive(Debug)]
-    struct Tree {
-        root: Option<Box<Node>>,
-    }
+impl<I: Iterator<Item = char>> LexemeIterator<I> {
+    pub fn new(iter: I) -> Self {
+        let mut trie = Tree::new();
 
-    fn build_tree() -> Tree {
-        let lexemes = Token::lexemes()
-            .iter()
-            .map(|(tok, _)| tok.clone())
-            .collect::<Box<_>>();
-
-        let mut tree = Tree {
-            root: Some(Box::new(Node::default())),
-        };
-
-        for tok in lexemes {
-            let lexeme = tok.lexeme().unwrap();
-            let mut current = &mut Box::new(Node::default());
-            let mut next = &mut tree.root;
-            let mut p = 0;
-            for c in lexeme.chars() {
-                current = next.get_or_insert(Box::new(Node::default()));
-                p = match current.keys.binary_search(&c) {
-                    Ok(p) => p,
-                    Err(p) => {
-                        current.keys.insert(p, c);
-                        current.values.insert(p, None);
-                        current.edges.insert(p, None);
-                        p
-                    }
-                };
-
-                next = current.edges.get_mut(p).unwrap();
-            }
-            current.values[p] = Some(tok);
+        for (token, token_str) in Token::lexemes() {
+            trie.insert(token_str.chars(), *token);
         }
 
-        tree
+        Self {
+            trie,
+            iter: iter.into(),
+        }
     }
 
-    fn search_tree(tree: &Tree, mut tokens: impl Iterator<Item = char>) -> Option<Token> {
-        let mut current = tree.root.as_ref().unwrap();
-        let mut p = None;
+    fn parse(&mut self) -> Option<Token> {
+        match self.trie.get_closest(&mut self.iter) {
+            Some((Some(key), token)) => {
+                // skip the peeked item
+                self.iter.set_once(key);
+                Some(*token)
+            }
+            Some((None, token)) => Some(*token),
+            None => None,
+        }
+    }
 
+    fn skip_whitespaces(&mut self) {
         loop {
-            let Some(ch) = tokens.next() else {
-                break;
-            };
+            let Some(c) = self.iter.next() else { break };
 
-            if crate::is_things::is_whitespace(ch) {
+            if is_things::is_whitespace(c) {
+                continue;
+            } else {
+                self.iter.set_once(c);
                 break;
             }
-
-            let n = match current.keys.binary_search(&ch) {
-                Ok(p) => p,
-                Err(p) => {
-                    eprintln!("No match for {ch} in {:?} (p={p})", current.keys);
-                    return None;
-                }
-            };
-
-            current = match current.edges.get(n) {
-                Some(Some(node)) => node,
-                _ => {
-                    p = Some(n);
-                    break;
-                }
-            };
-        }
-
-        eprintln!("current: {:?}", current);
-        current.values.get(p?).copied().flatten()
-    }
-
-    #[cfg(test)]
-    mod tree_tests {
-        use super::*;
-
-        #[test]
-        fn test_tree() {
-            use werkzeug::iter::AdvanceWhile;
-            let tree = build_tree();
-            eprintln!("Tree: {tree:?}");
-            let mut tokens = "fn let void+++(++bool)".chars();
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::Fn));
-            tokens.advance_while(|&c| crate::is_things::is_whitespace(c));
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::Let));
-            tokens.advance_while(|&c| crate::is_things::is_whitespace(c));
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::Void));
-            tokens.advance_while(|&c| crate::is_things::is_whitespace(c));
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::PlusPlus));
-            tokens.advance_while(|&c| crate::is_things::is_whitespace(c));
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::Plus));
-            tokens.advance_while(|&c| crate::is_things::is_whitespace(c));
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::OpenParens));
-            tokens.advance_while(|&c| crate::is_things::is_whitespace(c));
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::PlusPlus));
-            tokens.advance_while(|&c| crate::is_things::is_whitespace(c));
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::Bool));
-            tokens.advance_while(|&c| crate::is_things::is_whitespace(c));
-            assert_eq!(search_tree(&tree, &mut tokens), Some(Token::CloseParens));
-            assert_eq!(search_tree(&tree, &mut tokens), None);
         }
     }
 }
+
+impl<I: Iterator<Item = char>> Iterator for LexemeIterator<I> {
+    type Item = Token;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        // skip whitespace
+        self.skip_whitespaces();
+
+        self.parse()
+    }
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_iterator() {
+        let mut tokens = "fn let void+++(++bool)".chars();
+        let mut lexer = LexemeIterator::new(&mut tokens);
+        assert_eq!(lexer.next(), Some(Token::Fn));
+        assert_eq!(lexer.next(), Some(Token::Let));
+        assert_eq!(lexer.next(), Some(Token::Void));
+        assert_eq!(lexer.next(), Some(Token::PlusPlus));
+        assert_eq!(lexer.next(), Some(Token::Plus));
+        assert_eq!(lexer.next(), Some(Token::OpenParens));
+        assert_eq!(lexer.next(), Some(Token::PlusPlus));
+        assert_eq!(lexer.next(), Some(Token::Bool));
+        assert_eq!(lexer.next(), Some(Token::CloseParens));
+        assert_eq!(lexer.next(), None);
+    }
+}