Emacs defines 'w' class as word chars and '_' as set that together with 'w' can form identifiers. Note that by this operators in programming languages fall under punctuation '.' class and are treated as such by for example c-mode, java-mode, etc. It is confusing that characters defined in Haskell Report as 'symbol' are NOT the same as 'symbol' character class defined in Emacs.
The `find' invocation was only generating any output for *.hsc files.