1 files changed, 42 insertions, 0 deletions

diff --git a/crates/parser/src/token_set.rs b/crates/parser/src/token_set.rs
new file mode 100644
index 000000000..994017acf
--- /dev/null
+++ b/crates/parser/src/token_set.rs
@@ -0,0 +1,42 @@
+//! A bit-set of `SyntaxKind`s.
+
+use crate::SyntaxKind;
+
+/// A bit-set of `SyntaxKind`s
+#[derive(Clone, Copy)]
+pub(crate) struct TokenSet(u128);
+
+impl TokenSet {
+    pub(crate) const EMPTY: TokenSet = TokenSet(0);
+
+    pub(crate) const fn singleton(kind: SyntaxKind) -> TokenSet {
+        TokenSet(mask(kind))
+    }
+
+    pub(crate) const fn union(self, other: TokenSet) -> TokenSet {
+        TokenSet(self.0 | other.0)
+    }
+
+    pub(crate) fn contains(&self, kind: SyntaxKind) -> bool {
+        self.0 & mask(kind) != 0
+    }
+}
+
+const fn mask(kind: SyntaxKind) -> u128 {
+    1u128 << (kind as usize)
+}
+
+#[macro_export]
+macro_rules! token_set {
+    ($($t:expr),*) => { TokenSet::EMPTY$(.union(TokenSet::singleton($t)))* };
+    ($($t:expr),* ,) => { token_set!($($t),*) };
+}
+
+#[test]
+fn token_set_works_for_tokens() {
+    use crate::SyntaxKind::*;
+    let ts = token_set![EOF, SHEBANG];
+    assert!(ts.contains(EOF));
+    assert!(ts.contains(SHEBANG));
+    assert!(!ts.contains(PLUS));
+}