Problems With Smart Exceptions

Olivier BOUDEVILLE <>
Mon Dec 20 18:25:46 CET 2010


Hi,

I tried both versions (stable/devel) of the Smart Exceptions 
parse-transform (as taken from https://github.com/thomasl/smart_exceptions
), but had not luck with either.

With the stable version, correct user code produced then unwanted 
warnings, like "Warning: variable 'KeyIndex' exported from 'case' (line 
90)" for:

"""
  addEntry( Key, Value, HashTable ) ->

     KeyIndex = erlang:phash2( Key, size(HashTable) ) + 1,

     % Retrieve appropriate tuple slot:
     PreviousList = element( KeyIndex, HashTable ),

     NewList = replaceBucket( Key, Value, PreviousList, [] ),

     setelement(KeyIndex,HashTable,NewList).
"""
(line 90 is "KeyIndex = erlang:phash2( Key, size(HashTable) ) + 1"). 
Many warnings like this one appeared, in the transformed code.


With the devel version, I could check that the parse transform was 
compiled and found at compile-time, but even when using the sample code in 
http://www.erlang.org/faq/how_do_i.html#id55258 I still have the exact 
same message that was output when this parse-transform was not used:

''''
Erlang R14B01 (erts-5.8.2) [source] [64-bit] [smp:8:8] [rq:8] 
[async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.2  (abort with ^G)
1>  c(crash, [{parse_transform, smart_exceptions}]).
./crash.erl:9: Warning: no clause will ever match
{ok,crash}
2> crash:f().
** exception error: no match of right hand side value 5
      in function  crash:g/0
''''

Am I doing something wrong?

A last question: shouldn't we expect a performance penalty when using this 
parse-transform? I imagine that the transformed code could be (slighthly?) 
less efficient if having to test for more matchings/wrap more exceptions?

Thanks in advance for any information,
Best regards,

Olivier Boudeville.
---------------------------
Olivier Boudeville

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