Credence.Syntax.NoFnWithCapture (credence v0.8.0)

Repairs fn(&1 ...) — the fn keyword mistakenly mixed with capture syntax.

LLMs translating from other languages repeatedly emit fn(&1 > 0), gluing the fn keyword onto a capture body. In Elixir fn opens a clause that needs -> body end, so fn(&1 ...) never parses — the compiler reports a mismatched delimiter (the ) arrives where an end was expected). It is always a syntax error, so this is a REPAIR: the fix rewrites the leading fn( to &(, yielding the idiomatic capture form.

Only fn( immediately followed by a capture variable (&1, &2, …) is touched — fn(x) -> ... end (parenthesised parameters) is valid Elixir and a capture variable can never legally appear in that position, so the match fires exclusively on the malformed shape.

Bad (won't parse)

Enum.filter(list, fn(&1 > 0))

Good

Enum.filter(list, &(&1 > 0))