Glasgow University Computing Science Dept. Furthermore, perl is widely known, so we have chosen to follow its lead, rather than invent our extensions ex nihilo. We achieve this, essentially, by adding Perl-like features to Haskell. To keep matters short, we assume basic familiarity with both Haskell and Perl. That is one of the major points that Haskerl addresses.
Braces delimit such a comprehension.
I.e., the usual stuff. Because we still expect String regexp-matching to be the predominant use, we provide special pleading for it. While convenient, it just doesn't make sense for polymorphic regexps. Furthermore, there is quite a bit of FWIM syntax associated with various of these. And there will be FWIM fiddling, as above, when merited.