Programmatically Use Pattern Matching

Question

Is it possible to programmatically pattern match?

Pattern = {error, '_'},
IsError = 
    case {error, "foo"} of
        Pattern -> true;
        _ -> false
    end.

I know I can do this with macros, but I have a dynamic list of patterns I would like to match that aren't known ahead of time.

the question is kind of open, there are ways, but mostly depends on what you want to match and what patterns you have in mind, will you just match tuples? maps? any term at all? i.e. you can use something like Pattern Matching (5.7) (erlang.org/doc/apps/mnesia/mnesia_chap4) on mnesia, you still have to code it. yourself, but it is a known way of programmatically do pattern matching in erlang maybe some sample with the patterns you have in mind will help — rorra
– rorra, Commented Jul 8, 2022 at 18:06
@rorra Darn and it looks like that's specific to mnesia/ets/dets? Followed mensia:match_object all the way down to ets:match_object and that looks like a NIF so something I couldn't use outside of mnesia/ets/dets. github.com/erlang/otp/blob/master/lib/stdlib/src/ets.erl#L262 — micah
– micah, Commented Jul 11, 2022 at 14:40

legoscia · Accepted Answer · 2022-07-11 15:54:20Z

2

Perhaps the closest you can get is using a compiled match specification, by calling the functions ets:match_spec_compile and ets:match_spec_run:

MS = ets:match_spec_compile([{{error, '_'}, [], ['$_']}]).
Items = [ok, {error, foo}, {error, bar}].
ets:match_spec_run(Items, MS).

This returns the two items in the Items list that match:

[{error,foo},{error,bar}]

answered Jul 11, 2022 at 15:54

legoscia

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