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

[Goncalo Jorge Coelho e Silva]

(sorry about the message flood today ;) )

Ralph wrote:
>> inter.m:094: error: the language construct =/2 should be 
>> inter.m:094: used as a goal, not as an expression. 
>> inter.m:094: If you are trying to use a goal as a boolean function, 
>> inter.m:094: you should write `if <goal> then yes else no' instead. 
>> make: *** [run] Error 1 
>
>The error message seems very clear. 

Not to me I'm affraid. I tried to write the `if <goal> then yes else no'
code suggestion but 'yes' and 'no' come up as "error: undefined predicate 
`yes/0'"

Besides, I find no problem with this simple condition, for it to be
considered a goal:


	...
        lookup(RegistHashIn, "mode") = ModeIn,
        (
        if {ModeIn = 0} then
                %unify(Xi,S)
                {io__write_string(" Update Unify - unify_value ")}
           else
                array__set(HeapIn, H, Xi, HeapOut),
                NewH = H + 1,
                set(RegistHashIn, "h", NewH) = RegistHash01
        ),
	...

Thanks,
Goncalo






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