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Erlang code snippet....

Code like that:

blah(X) ->
  X1 = f(X),
  X2 = g(X1),
  X3 = h(X2),
  i(X3).

is very error prone, and worse very hard to extend. Just adding another
function application between f(X) and g(X1) requires you to alter all lines
upto the end of the function:

blah(X) ->
  X1 = f(X),
  X2 = j(X1)
  X3 = g(X2),
  X4 = h(X3),
  i(X4).

This causes 2*numberoflinestoendoffunction potential error sources;

And this is also not at all a very functional style.
Why not rewriting it like this:

blah(X) -> 
    (chain([
       f,
       g,
       h,
       i
      ]))(X).

where one chains together the functions. Adding a function invocation in between is as easy as pie.



chain(FunList) ->
  lists:foldl(
    fun combine/2,
    fun id/1,
    FunList). 
 
id(X) -> X.

combine(F,G) ->
    RF = to_local_function(F),
    RG = to_local_function(G),
    fun(X) ->
     RF(RG(X))
    end.

to_local_function(F) ->
    case F of 
 {FM, FF} -> F;
 _ when is_atom(F) -> {?MODULE, F}
    end.

Another solution might be using the state monad, wich was
built for dealing with this kind of functional composition.

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