[mercury-users] typeclass question #2

[Fergus Henderson]

On 02-May-2001, Terrence Brannon <princepawn at earthlink.net> wrote:
> 
> :- type rgb
>         ---> rgb(
>                 int,
>                 int,
>                 int
>         ).
> 
> :- type coloured_coordinate
>         ---> coloured_coordinate(
>                 float,
>                 float,
>                 rgb
>         ).
> 
> .... I would have done this a different way:
> 
> :- type coordinate --->
>   coordinate (float,float).
> 
> type colored_coordinate %correct spelling :-)
>    ---> colored_coordinate(
>            coordinate,
>            rgb
> 	   ).

Yes, that is probably better design, in fact.

> ... then I tried to figure out how to write methods to do the two
> levels of indirection but
>   a - the samples directory has no typeclasses
>   b - the library directory has one: enum, but only an interface and
>       no implementation.

There are instances of enum in the other library modules:
bool.m, char.m, int.m, term.m.

There are also some examples in the "tests" distribution,
in the directory tests/hard_coded/typeclasses.  

(However, these examples where not specifically designed for pedagogical
purposes.)

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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