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]),
	[parse(X) || X <- Ast],
	Ast.

parse({function, _Line, _FunName, _ArgNum, Clause}) ->
	[parse(X) || X <- Clause];

parse({clause, _Line, _Vars, _Gaurd, ExprCalls}) ->
	[erl_eval:expr(X, erl_eval:new_bindings()) || X <- ExprCalls];

parse(_) -> ok.