How to use Parse Transform feature in Erlang for meta-programming.

main.erl

-module(main).
-export([hi/0, bye/0, hey/1]).
-compile({parse_transform, main_pt}).

hi() -> io:format("Hi there!~n").
bye() -> io:format("Bye there!~n").
hey(foo) -> io:format("Hey foo!~n");
hey(bar) -> io:format("Hey bar!~n").

main_pt.erl

-module(main_pt).
-export([parse_transform/2]).

parse_transform(Ast, _Opt) ->
	io:format("AST:~p~n",[Ast]),
        Ast2 = [parse(Tuple) || Tuple <- Ast],
        if Ast =:= Ast2 -> io:format("AST2 == AST !~n");
                   true -> io:format("AST2:~p~n",[Ast2]) end,
        Ast2.

parse({function,Line, FunName, ArgNum, Clauses}) ->
	{function, Line, FunName, ArgNum, [parse(Clause) || Clause <- Clauses]};

parse({clause, _Line, _Vars, _Guard, [Call]}=Tuple) ->
	erl_eval:expr(Call, erl_eval:new_bindings()),
        Tuple;

parse(Tuple) -> Tuple.