[erlang-questions] How can I make a list of this

[Richard A. O'Keefe]

On 19/08/2015, at 11:10 pm, Roelof Wobben <r.wobben@REDACTED> wrote:
> 
> Still my question stands. How do I get a nice list of the ourcome of the exports of the functions ot more then 1 module.
> I now have a list of list of tuples where every list is the outcome of 1 module.

Step 1.
Module:module_info() ->
  [ {exports, List_Of_Exports}
  , {imports, List_Of_Imports}
  , {attributes, List_Of_Attributes}
  , {compile, Information_About_Compiler_Source_And_Options}
  ...
  ].

A little familiarity with the standard libraries suggests
that if f(Args) returns a list of {Key,Value} pairs then
f(Args,Key) might return just the Value you are interested
in.  Play with it in the shell and discover that it is true.

Step 2.
Module:module_info(exports) ->
  a list of {Name,Arity} pairs, just the exports we wanted.

Step 3.
You already know about list comprehension.
You may not realise that you can have more than one
generator (Pattern <- List) in a list comprehension
and that these operate as nested loops.

all_exports(Modules) ->
    [  {Module,Name,Arity}
    || Module <- Modules,
       {Name,Arity} <- Module:module_info(exports)
    ].

You could try this in the shell:

Modules = [orddict, proplists],
Triples = [  {Module,Name,Arity}
          || Module <- Modules,
             {Name,Arity} <- Module:module_info(exports) ].

Step 4.
If you want the list sorted on module, then name within module,
then arity within name within module, you can just use
lists:sort(Triples).

Now suppose we want that listed sorted by Name, then Arity,
then Module.  You have to write your own comparison function,
but that's not hard.

Compare = fun ({M1,F,N}, {M2,F,N}) -> M1 =< M2
            ; ({_,F,N1}, {_,F,N2}) -> N1 =< N2
            ; ({_,F1,_}, {_,F2,_}) -> F1 =< F2
          end,
lists:sort(Compare, Triples).

(try-it-in-the-shell code tested)