[mercury-users] this appears to be a mixin

[Ralph Becket]

> From: Terrence Brannon [mailto:tmbranno at oracle.com]
> Sent: 10 July 2001 05:28
> 
> I'm not sure what sort of angle the Mercury book will be taking in
> comparison to the Language Reference Manual, but I hope that it is
> full of completely working pragmatic examples.
> 
> Also, I think the book will be hard to write because at any point when
> discussing Mercury you must be conscious of the (at least) 3 types of
> audiences that may be reading it: those from the imperative,
> object-oriented, or functional perspectives.

Two (possibly three) books are contemplated: a tutorial, something
for L/FP experts, and possibly a "Mercury for the Real World" type
affair.  Working examples should be de rigeur.

> But anyway, my feeling is that the code below was not described as a
> mixin, when it does in fact appear to be so.
> 
> :- pred distance(P1, P2, float) <= (point(P1), point(P2)).
> :- mode distance(in, in, out) is det.
> 
> distance(A, B, Distance) :-
>         coords(A, Xa, Ya),
>         coords(B, Xb, Yb),
>         XDist = Xa - Xb,
>         YDist = Ya - Yb,
>         Distance = sqrt(XDist*XDist + YDist*YDist).

Having searched around on the web for a definition, it's still not
clear to me exactly what constitutes a mixin class.  As far as I
can work out, mixin classes are pretty much the same thing as
Java/C# interfaces - that is, something inheriting from a mixin 
class must provide its own implementations for the method signatures
specified in the mixin class.  On this basis, type classes are very
similar to interfaces/mixin classes since they do not provide
implementation inheritance.

- Ralph
--------------------------------------------------------------------------
mercury-users mailing list
post:  mercury-users at cs.mu.oz.au
administrative address: owner-mercury-users at cs.mu.oz.au
unsubscribe: Address: mercury-users-request at cs.mu.oz.au Message: unsubscribe
subscribe:   Address: mercury-users-request at cs.mu.oz.au Message: subscribe
--------------------------------------------------------------------------