1 files changed, 7 insertions, 5 deletions
diff --git a/isabelle-unicode/src/lib.rs b/isabelle-unicode/src/lib.rs
index 8394e57..30a7cec 100644
--- a/isabelle-unicode/src/lib.rs
+++ b/isabelle-unicode/src/lib.rs
@@ -1,13 +1,15 @@
 
 symbolmacro::make_symbols!();
 
-// TODO: is it possible to be polymorphic over slice types here?
 pub trait PrettyUnicode {
-    fn to_pretty_unicode(self) -> Option<String>;
+    type Owned: core::borrow::Borrow<Self>;
+    fn to_pretty_unicode(&self) -> Option<Self::Owned>;
 }
 
-impl PrettyUnicode for &str {
-    fn to_pretty_unicode(self) -> Option<String> {
+impl PrettyUnicode for str {
+    type Owned = String;
+
+    fn to_pretty_unicode(&self) -> Option<Self::Owned> {
         // split at escape sequences
         let mut chunks = self.split("\\<");
 
@@ -30,7 +32,7 @@ impl PrettyUnicode for &str {
 
                 // how much of the rest do we need?
                 let offset = ident?
-                .len()
+                    .len()
                     + 1;
                 Some((symbol, &chunk[offset..]))
             })