How to do Erlang pattern matching using regular expressions?

Question

When I write Erlang programs which do text parsing, I frequently run into situations where I would love to do a pattern match using a regular expression.

For example, I wish I could do something like this, where ~ is a "made up" regular expression matching operator:

my_function(String ~ ["^[A-Za-z]+[A-Za-z0-9]*$"]) ->
    ....

I know about the regular expression module (re) but AFAIK you cannot call functions when pattern matching or in guards.

Also, I wish matching strings could be done in a case-insensitive way. This is handy, for example, when parsing HTTP headers, I would love to do something like this where "Str ~ {Pattern, Options}" means "Match Str against pattern Pattern using options Options":

handle_accept_language_header(Header ~ {"Accept-Language", [case_insensitive]}) ->
    ...

Two questions:

1. How do you typically handle this using just standard Erlang? Is there some mechanism / coding style which comes close to this in terms of conciseness and easiness to read?

2. Is there any work (an EEP?) going on in Erlang to address this?

Answer 1

You really don't have much choice other than to run your regexps in advance and then pattern match on the results. Here's a very simple example that approaches what I think you're after, but it does suffer from the flaw that you need to repeat the regexps twice. You could make this less painful by using a macro to define each regexp in one place.

-module(multire).

-compile(export_all).

multire([],_) ->
    nomatch;
multire([RE|RegExps],String) ->
    case re:run(String,RE,[{capture,none}]) of
    match ->
        RE;
    nomatch ->
        multire(RegExps,String)
    end.


test(Foo) ->
    test2(multire(["^Hello","world$","^....$"],Foo),Foo).

test2("^Hello",Foo) ->
    io:format("~p matched the hello pattern~n",[Foo]);
test2("world$",Foo) ->
    io:format("~p matched the world pattern~n",[Foo]);
test2("^....$",Foo) ->
    io:format("~p matched the four chars pattern~n",[Foo]);
test2(nomatch,Foo) ->
    io:format("~p failed to match~n",[Foo]).