> It uses the pcre-heavy Haskell library which in turn calls out to the system-wide pcre C library for actually compiling and running the regex.

That's not true regular expressions, but a backtracker with eclectic features.

The regex used in the regex solution is just:

  mul\((\d+),(\d+)\)

If Haskell happens to provide bindings to the POSIX regcomp/regexec stuff, that would be something to try instead. \d has to be replaced with [0-9], needless to say.