Meeting Follow-Up: Processing User Input

[Eric Ivancich]

Hi Everyone,

I enjoyed last night's meeting, and I cleaned up my code quite a bit
as a result.

One issue we were dealing with was processing user terminal input.
This works, although if you were testing against two or more regexps,
it would be pretty clunky:

UserInput = io:get_line('(h)it or (s)tand? '),
Hit = case regexp:match(UserInput, "^[hH]") of
{match, _, _} -> yes;
nomatch -> no
end,

But what we really want is to test a string against a list of regexps
and returning some identifier when we find one that matches. I think
that's the solution Patrick envisioned and proposed. Well here's some
code:

% any_match/2 takes a string and a list, where each element of the
% list is a tuple containing a regular expression and match-value.
% Each regexp in the list is tested, in order, against the string, and
% when the first matches, it's match-value is returned. If no regexps
% match the string, then the atom 'nomatch' is returned.

any_match({match, _, _}, MatchValue, _String, _List) -> MatchValue;
any_match(nomatch, _MatchValue, _String, []) -> nomatch;
any_match(nomatch, _MatchValue, String, [{Regexp, MatchValue} | Rest])
->
any_match(regexp:match(String, Regexp), MatchValue, String, Rest).

any_match(String, MatchList) -> any_match(nomatch, ignored, String,
MatchList).

And that allows you to code something like this:

case any_match(UserInput, [{"^[Hh]", hit}, {"^[Ss]", stand}]) of
hit ->
% code for hit;
stand ->
% code for stand;
nomatch ->
io:format("Illegal input ~p.~n", [UserInput]),
% recurse so user can try again
end

Eric