Matching Regular Expressions with OCaml Patterns

This syntax extension turns

match%pcre x with
| {|re1|} -> e1
...
| {|reN|} -> eN
| _ -> e0

into suitable invocations to the ocaml-re library. The patterns are plain strings of the form accepted by Re_pcre, except groups can be bound to variables using the syntax (?<var>...). The type of var will be string if a match is of the groups is guaranteed given a match of the whole pattern, and string option if the variable is bound to or nested below an optionally matched group.