identity parse transform using syntax_tools

Ulf Wiger (AL/EAB) <>
Mon Feb 13 14:40:18 CET 2006


I thought this might be of some use to those out there
writing parse transforms.

I simplified my plain_fsm_xform module into an entity
parse transform callback.

The main point is of course that a parse transform
based on syntax_tools should be much more stable
in time than cloning erl_id_trans and hacking it.

The actual work is done in a fun:

    Fun = fun(Type, Form, Context, Acc) ->
		  io:format("Type    = ~p~n"
			    "Form    = ~p~n"
			    "Context = ~p~n"
			    "Acc     = ~p~n", [Type, Form, Context,
Acc]),

		  {Form, _Recurse = true, Acc+1}
	  end,

and the parse_transform callback looks like this:

parse_transform(Forms, _Options) ->
    Fun = fun(Type, Form, Context, Acc) ->
		  ...
	  end,
    {NewTree, _} = transform(Forms, Fun, _Acc = 1),
    [erl_syntax:revert(T) || T <- lists:flatten(NewTree)].

The Recurse flag can be set to false if there is
no need to traverse the subtrees of a particular 
form. Perhaps an unnecessary optimization...

I haven't tested it much - basically just compiling
a module and checking that the printouts look ok.

I've attached the module. Let me know what you think.

Regards,
Ulf W




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