diff --git a/TODO.md b/TODO.md
index 1c57b1b..8ed4158 100644
--- a/TODO.md
+++ b/TODO.md
@@ -8,6 +8,7 @@ DONE -experiment with storing metadata via ItemIds on AST nodes (cf. https://rus
 - standardize on an error type that isn't String
 -implement a visitor pattern for the use of scope_resolver
   - maybe implement this twice: 1) the value-returning, no-default one in the haoyi blogpost,
+  -look at https://gitlab.haskell.org/ghc/ghc/wikis/pattern-synonyms
                                 2) the non-value-returning, default one like in rustc (cf. https://github.com/rust-unofficial/patterns/blob/master/patterns/visitor.md)
 
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