[mercury-users] boolean expressions from semidet predicates

[Mark Brown]

On 21-Apr-2006, Nicholas Nethercote <njn at csse.unimelb.edu.au> wrote:
> Hi,
> 
> I want to write something like this:
> 
>   require((0 < X) and (X < 10))
> 
> But I can't work out if it's possible to combine semidet operations in this 
> way.  'and' doesn't work, '/\' doesn't work (I'm not even sure what 'and' 
> and '/\' are, since the reference manual seems to only list the operators 
> without explaining what they do),

It's only concrete syntax.  `X and Y' means the same thing as `and(X, Y)'.

As for what they "are": `/\' is ISO-Prolog and `and' is an NU-Prolog
extension.

> and ',' doesn't work because you can't 
> have a goal inside require/1.

The argument to require/1 is a closure.  You can use an explicit lambda
expression or use the `Term(Args)' shorthand (of which `0 < X' is an
example).

> 
> Is this possible,

You can always define `and/2' and `or/2' to mean conjunction and
disjunction.  Or think of a meaningful name for your condition and
define a predicate that does what you want.

Cheers,
Mark.

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