Comments on: Searching the abstract form in erlang

By: John Bender

John Bender — Fri, 24 Apr 2009 20:54:31 +0000

@Hynek

I agree they are hard to debug (for example the Name in checking for a function), but without my desired

 {something, _, _} == OtherThing

its the quickest solution for providing a “Matcher” of sorts.

By: Hynek (Pichi) Vychodil

Hynek (Pichi) Vychodil — Fri, 24 Apr 2009 19:29:07 +0000

And one more suggestion, avoid using macros on all places where functions or high order functions can be used. It is necessary only for pattern matching. If you are afraid about performance use -code(inline). or explicit -compile({inline, [{turn_cw, 1}, {turn_ccw, 1}]}). You can use it even in .hrl files. To suppress unused function warnings you should use -compile({nowarn_unused_function, [{turn_cw, 1}, {turn_ccw, 1}]}). for your checks you can introduce

-export([call_check/1, function_check/1]).

call_check(Name) ->
  fun(Form) ->
    case Form of
      {call,_,{atom,_,Name},_} -> true;
      _ -> false
    end
  end.

function_check(Name) ->
  fun(Form) ->
    case Form of
      {function,_,Name,_,_} -> true;
      _ -> false
    end
  end.

and usage:

foo(Form, Name) ->
    find(Form, util:call_check(Name)).

or even in .hrl:

%if there are performance reasons
%-compile({inline, [{call_check, 1}, {function_check, 1}]}).

%avoid warning
-compile({nowarn_unused_function, [{call_check, 1}, {function_check, 1}]}).

call_check(Name) ->
  fun(Form) ->
    case Form of
      {call,_,{atom,_,Name},_} -> true;
      _ -> false
    end
  end.

function_check(Name) ->
  fun(Form) ->
    case Form of
      {function,_,Name,_,_} -> true;
      _ -> false
    end
  end.

uasge:

-include("util.hrl").

foo(Form, Name) ->
    find(Form, call_check(Name)).

Macros are hard to debug and maintenance.

By: John Bender

John Bender — Fri, 24 Apr 2009 18:44:59 +0000

@Hynek

The head matching in a fun is awesome, I hadn’t even considered doing that as I’ve never seen it before. That is super clean.

By: Hynek (Pichi) Vychodil

Hynek (Pichi) Vychodil — Fri, 24 Apr 2009 18:37:37 +0000

Another suggestion:

-define(call_check, fun({call,_,{atom,_,Name},_}) -> true;
                       (_) -> false
                    end).

-define(function_check, fun({_, _, Name, _, _}) -> true;
                           (_) -> false
                        end).

By: John Bender

John Bender — Thu, 23 Apr 2009 16:35:38 +0000

@Hynek

That erl_syntax_lib was probably what I was looking for when I was on #erlang the other night. Didn’t get a response, but thanks for the insight!

By: Hynek (Pichi) Vychodil

Hynek (Pichi) Vychodil — Thu, 23 Apr 2009 15:24:39 +0000

find(Form, CompareFun) when is_list(Form) ->
[ Y || X <- Form, Y <- find(X, CompareFun) ].
find(Form, CompareFun) ->
lists:reverse(
erl_syntax_lib:fold(
fun(N, R) ->
case CompareFun(N) of
true -> [N|R];
_ -> R
end
end, [], X
)
).