Thursday, September 10, 2009

Removing warnings from ct_expand

I use ct_expand alot (can you tell?). The released version outputs warnings about unused variables, which are harmless, except ... that it conditioned me to ignore unused variable warnings from the compiler. Then the other day I had a real bug which the compiler was warning me about (via an unused variable) that took me quite a bit of time to find. Lesson learned: make sure that a correct compile is as quiet as possible, so problems stand out.

Ulf gave me some pointers on how to prevent ct_expand from emitting these warnings. Basically, ensure that the temporary variables created by ct_expand are prefixed with an underbar. Here's a patch:

--- src/ct_expand.erl 5 Jun 2009 21:07:32 -0000 1.1
+++ src/ct_expand.erl 10 Sep 2009 04:12:07 -0000
@@ -139,6 +139,9 @@
{Fname, Arity} = erl_syntax_lib:analyze_function(Form),
VarNames = erl_syntax_lib:new_variable_names(
+ fun (N) ->
+ list_to_atom ("_V" ++ integer_to_list (N))
+ end,
{Form, [{function, Fname},
{arity, Arity},

1 comment:

Ulf Wiger said...

I'm glad it worked.

If you have time, It'd be great if you could give my new ct_expand a spin.

It shouldn't suffer from this problem at all, and has at least one additional useful feature: optional pretty-printing of the transformed code.

Documentation is catching up, but still leaves something to be desired. Contact me to resolve any confusion that it may cause.