[mercury-users] very minor variable printing bug

Nicholas Nethercote njn at csse.unimelb.edu.au
Fri Oct 26 13:23:39 AEST 2007


It's not a big deal, but I thought I'd mention it:  if you have a variable 
whose name begins with "V_" in a Mercury program, it seems that any 
error message that mentions it prepends it with an additional "V_".
Eg. in this type-incorrect line from a program I wrote:

         VArray = [0-V_2, 1-V_1, 2-V_0],

I get an error message:

p.m:035: In clause for predicate `problem'/1:
p.m:035:   in list element #0:
p.m:035:   in unification of argument
p.m:035:   and term `(V_42 - V_V_2)':
p.m:035:   type error in argument(s) of functor `-/2'.
p.m:035:   Argument 2 (V_V_2) has type `(fd.fdvar)',
p.m:035:   expected type was `((fd.expression).var_expression)'.

If I change V_2 to, say, Z_2, it's printed correctly as "Z_2".

Maybe it's intended behaviour, but it took me a minute to work out what was 
happening when I first saw it.

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