[mercury-users] type class bug?

[Nicholas Nethercote]

Hi,

I'm trying to use a type class.

I have these declarations:

   :- typeclass pstr(T) where [ func pstr(T) = string ].

   :- instance pstr(raw_item)  where [ func(pstr/1) is pstr_raw_item  ].
   :- instance pstr(type_expr) where [ func(pstr/1) is pstr_type_expr ].
   %:- instance pstr(expr)      where [ func(pstr/1) is pstr_expr      ].

This compiles fine.

If I uncomment the last line, I get this error:

   Mercury/cs/zinc.c:1144: error: redefinition of 'mercury_data_base_typeclass_info_zinc__pstr__arity1__pair__pair__arity2__'
   Mercury/cs/zinc.c:1135: error: previous definition of 'mercury_data_base_typeclass_info_zinc__pstr__arity1__pair__pair__arity2__' was here

In the zinc.c file the offending duplicate code looks like this:

   const MR_BaseTypeclassInfo
   mercury_data_base_typeclass_info_zinc__pstr__arity1__pair__pair__arity2__[] = {
         (MR_Code *) 0,
         (MR_Code *) 0,
         (MR_Code *) 0,
         (MR_Code *) 1,
         (MR_Code *) 1,
         MR_MAYBE_STATIC_CODE(MR_ENTRY_AP(fn__zinc__ClassMethod_for_zinc__pstr____pair__pair__arity2______zinc__pstr_1_1_0))
   };

The types 'type_expr' and 'expr' look like this:

   :- type type_expr == pair(raw_type_expr, src_locn).
   :- type expr == pair(raw_expr, src_locn).

It seems like these are similar enough that Mercury gets confused.

Is this a bug?  I'm using:

   Mercury Compiler, version rotd-2006-05-26, configured for i686-pc-linux-gnu

Thanks.

Nick
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