High Order Functions must be tested before use

From my previous article comments it is a small and efficient method of filtering datas:

Cpu = fun({cpu, _, _}) -> true; (_) false end.

But whenever we want to transposing it into a HOF (high order function):

Filter = fun(Elem) ->
 fun({Elem, _, _}) -> true; (_) false end
 end.

This naive approach doesn't work:

1> Filter = fun(Elem) -> fun({Elem, _, _}) -> true; (_) -> false end end. 
#Fun<erl_eval.6.49591080>
2> C = Filter(cpu).
#Fun<erl_eval.6.49591080>
3> C({test, t, t}).
true % this should have been false ...

As explained in this document, we need to use guards to make our high order function effective:

The rules for importing variables into a fun has the consequence that certain pattern matching 
operations have to be moved into guard expressions and cannot be written in the head of the fun. 

The correct way is:

Filter = fun(Elem) ->
 fun({X, _, _}) when X == Elem -> true; (_) false end
 end.

So we must keep in mind that sometimes we should really check that our HOF is working as expected !