[mercury-users] =/2 used as a goal, not as an expression

[Goncalo Jorge Coelho e Silva]

Hi,
 
>`yes' and `no' are defined in the bool module in the library. 

OK. So I tried to import it and then run the code again with
this predicate in it:

 What's wrong here? According to the compiler message,
this should work.


(with ":-import bool." on)
--------------------------

:- pred test(int).
:- mode test(in) is det.
test(Input):- if {Input = 0} then yes else no.

inter.m:660: In clause for predicate `inter:test/1':
inter.m:660:   in argument 1 of call to predicate `{}/1':
inter.m:660:   error: the language construct =/2 should be
inter.m:660:   used as a goal, not as an expression.
inter.m:660:   If you are trying to use a goal as a boolean function,
inter.m:660:   you should write `if <goal> then yes else no' instead.
inter.m:660: In clause for predicate `inter:test/1':
inter.m:660:   error: undefined predicate `{}/1'.
inter.m:660: In clause for predicate `inter:test/1':
inter.m:660:   error: undefined predicate `yes/0'.
inter.m:660: In clause for predicate `inter:test/1':
inter.m:660:   error: undefined predicate `no/0'.
make: *** [run] Error 1


or using DCGs:
--------------

inter.m:658: Error: no clauses for predicate `inter:test/1'.
inter.m:661: In clause for predicate `inter:test/3':
inter.m:661:   error: undefined predicate `yes/2'.
inter.m:661: In clause for predicate `inter:test/3':
inter.m:661:   error: undefined predicate `no/2'.
make: *** [run] Error 1


:- pred test(int).
:- mode test(in) is det.
test(Input)--> if {Input = 0} then yes else no.





 on the other sample code:
---------------------------


 I took some parts of the last sample code off, to 
show the least non-relevant code possible. So, yes,
it was a DCG predicate and yes, I made a mistake on
using {..} on IO io__write_string. I use DCG code 
with IO because, originaly, most of it is written
with no IO code at all. Eventually I have to pop
some in to test some aspects of it.

 Here's a whole predicate with the same problem.
How can I put 
	        if {ModeIn = 0} then
 to work?? (I believe there isn't any {...} error
here!)


inter.m:624: In clause for predicate `inter:code_gen/7':
inter.m:624:   in argument 1 of call to predicate `{}/1':
inter.m:624:   error: the language construct =/2 should be
inter.m:624:   used as a goal, not as an expression.
inter.m:624:   If you are trying to use a goal as a boolean function,
inter.m:624:   you should write `if <goal> then yes else no' instead.
inter.m:624: In clause for predicate `inter:code_gen/7':
inter.m:624:   error: undefined predicate `{}/1'.
make: *** [run] Error 1


624: >        if {ModeIn = 0} then



code_gen(instruction("unify_variable",Xi,""), HeapIn, HeapOut,
RegistHashIn, RegistHashOut) -->
        {
        lookup(RegistHashIn, "h") = H,
        lookup(RegistHashIn, "mode") = ModeIn,
        lookup(RegistHashIn, "s") = S,
        (
        if {ModeIn = 0} then
                array__lookup(HeapIn, S, SContent),
                string__det_to_int(SContent) = SConverted,
                set(RegistHashIn, Xi, SConverted) = RegistHashOut
                %(?)set(RegistHashIn, Xi, SContent) = RegistHash01,
                %(?)NewS = S + 1,
                %(?)set(RegistHash01, "s", NewS) = RegistHashOut
           else
                array__set(HeapIn, H, "REF", Heap01),
                string__int_to_string(H+1, ConvertedInt),
                array__set(Heap02, H+1, ConvertedInt, Heap03),
                set(RegistHashIn, Xi, H) = RegistHash01,
                set(RegistHash01, "h", NewH) = RegistHash02,
                NewH = H + 2,
                set(RegistHash02, "h", NewH) = RegistHash03
        ),
        NewS = S + 1,
        set(RegistHash03, "s", NewS) = RegistHashOut
        }.


Thanks,
Goncalo



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