[m-dev.] subtyping proposal (repost)

[Tyson Dowd]

I prefer the second syntax, it is simpler.

Also the last example in the proposal is incorrect.

:- subtype io__bidirectional_stream < io__text_stream
	---> io__stream(_, _, yes, _).

should be

:- subtype io__bidirectional_stream < io__text_stream
	---> io__stream(_, yes, yes, _).

or

:- subtype io__bidirectional_stream < io__input_stream
	---> io__stream(_, _, yes, _).


I'm a little unclear on what you mean in your proposal about 
"abstract, but conceptually defined as follows".  What is the 
Mercury syntax for conceptual definitions?

I personally think this language feature is sorely missed, and I can
think of a number of places I'd like to use it already.

-- 
       Tyson Dowd           # 
                            #  Surreal humour isn't eveyone's cup of fur.
     trd at cs.mu.oz.au        # 
http://www.cs.mu.oz.au/~trd #
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