1 files changed, 58 insertions, 0 deletions
diff --git a/src/syntax/ident.rs b/src/syntax/ident.rs
new file mode 100644
index 00000000..5ab7c73c
--- /dev/null
+++ b/src/syntax/ident.rs
@@ -0,0 +1,58 @@
+//! Unicode identifiers.
+
+use std::ops::Deref;
+
+use unicode_xid::UnicodeXID;
+
+/// An identifier as defined by unicode with a few extra permissible characters.
+///
+/// This is defined as in the [Unicode Standard], but allows additionally
+/// `-` and `_` as starting and continuing characters.
+///
+/// [Unicode Standard]: http://www.unicode.org/reports/tr31/
+#[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct Ident(pub String);
+
+impl Ident {
+    /// Create a new identifier from a string checking that it is a valid.
+    pub fn new(ident: impl AsRef<str> + Into<String>) -> Option<Self> {
+        if is_ident(ident.as_ref()) {
+            Some(Self(ident.into()))
+        } else {
+            None
+        }
+    }
+
+    /// Return a reference to the underlying string.
+    pub fn as_str(&self) -> &str {
+        self
+    }
+}
+
+impl AsRef<str> for Ident {
+    fn as_ref(&self) -> &str {
+        self
+    }
+}
+
+impl Deref for Ident {
+    type Target = str;
+
+    fn deref(&self) -> &Self::Target {
+        self.0.as_str()
+    }
+}
+
+/// Whether the string is a valid identifier.
+pub fn is_ident(string: &str) -> bool {
+    let mut chars = string.chars();
+    if matches!(chars.next(), Some(c) if c.is_xid_start() || is_also_ok(c)) {
+        chars.all(|c| c.is_xid_continue() || is_also_ok(c))
+    } else {
+        false
+    }
+}
+
+fn is_also_ok(c: char) -> bool {
+    c == '-' || c == '_'
+}