I incorporated regexp literal in Gauche Scheme and found it very handy. Regexp literal is written as #/pattern/. When appears in the procedure position it also works as a matcher.
(#/\d+/ "abc123") => #<match object>
The matcher returns a match object if the given string matches the pattern; you can extract submatches from it. The match object also works like a procedure.
The good thing I found about this "acts like a procedure" feature is that I can pass around it wherever a procedure is expected. For example, grep can be expressed in terms of the standard 'filter' procedure.
(filter #/\w+/ list-of-strings)
(I'm not sure Arc can go this direction, since Arc's operators that takes predicates (e.g. 'find', 'some', 'all', ...) does "auto-testification"---if a given object isn't a procedure, it creates a predicate that tests equality to the given object---which may conflict with this type of extended use of "callable objects".)
