[mercury-users] Restricted types with inst declarations? ELL type/inst usage?

[David Overton]

doug.auclair at logicaltypes.com wrote:
> Dear Ian, thank you for the inst question solution!  You also wrote:
>
>
>>But why don't you just do:
>>
>>:- type bit
>>	--->	one
>>	;		zero.
>>
>>I think that would make your life simpler.
>
> You are absolutely right on all counts.  So thank you for humouring me
> on this inst issue.  It's also a question of (*sigh*) semantics and
> conciseness.  1 and 0 are fairly strongly embedded into the mode of
> discourse, so reading something in the code like:
>
> Rule0 = [111 - 0, 110 - 0, 101 - 0, 100 - 1, 011 - 1, 010 - 1, 001 -
1, 000 - 0]
>
> is much easier for one to grasp* than
>
> Rule1 = [[one, one, one] - zero, [zero, one, one] - zero, [one, zero,
one] - zero, [zero, zero, one] - one,
>             [one, one, zero] - one, [zero, one, zero] - one, [one,
zero, zero] - one, [zero, zero, zero] - zero] +
>
>
> and, having Rule0 be proved type-correct at compile-time is the
benefit I'm looking for.

If you need to use the symbols 0 and 1 then how about

:- type bit
	--->	'0'
	;	'1'.

?

David
-- 
David Overton
http://www.overtons.id.au/
http://flickr.com/photos/overton/
Mobile: +44 7799 344 322
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