Unraverl

Unraverl is a parse transform library for erlang. You can run your module through the transformation by including the following attribute at the top of your module:

-compile([{parse_transform, unraverl}]).

Its rough around the edges and has no testing or build scripts at this point, but feel free to play around.

This parse transform provides two facilities:

Filters

By defining filters as attributes at the beginning of your module, unraverl will create a function chain for you, removing the need for extra calls inside the filtered functions.

In the following example both prepend and append have the all_lists function applied as a before filter to make sure that all arguments passed are lists. Additionally, the to_atom function is applied as an after filter to make sure that the result is an atom.

-before_exec({[prepend, append], all_lists}).
-after_exec({[prepend, append], to_a_atom}).

prepend(S1, S2) ->
    S1 ++ S2.

append(S1, S2) ->
    S2 ++ S1.

all_lists(Objects) when is_list(Objects)->
    lists:map(fun to_list/1, Objects).

to_list(Object) when is_number(Object) ->
    lists:flatten(io_lib:format("~w" , [Object]));

to_list(Object) when is_atom(Object) ->
    atom_to_list(Object); 

to_list(Object) when is_binary(Object) ->
    binary_to_list(Object);

to_list(Object) when is_tuple(Object) ->
    tuple_to_list(Object); 

to_list(Object) when is_list(Object) ->
    Object.

to_atom(List) when is_list(List) ->
    Result = list_to_atom(lists:flatten(List)),
    Result.

Obviously since we aren't able to modify global state with our filters they must alter the incoming arguments and as a result there are constraints on the arity of the filter function. Either the arity must match that of the function being filtered or it must take exactly one argument as a list of the arguments being passed.

Partial Application

Whenever a local function call is made within a module where the arity of the call is less than the next highest arity function definition, the call will be replaced by a fun definition requiring the remaining arguments.

add(L, R) -> L + R. 

foo() -> add(1). 

In most cases this would give you a compile error, but unraverl replaces foo with.

foo() -> fun(R) -> add(1, R) end.

Cheers!