[m-users.] Existential types example

[Volker Wysk]

P.S.:

> I've tried the following example from the Mercury Language Reference Manual,
> section 11.3 Existentially typed data types:
> 
> 
> :- typeclass showable(T) where [ func show(T) = string ].
> 
> :- type s
>     --->    some [T] (s(T) => showable(T)).
> 
> :- type list_of_showable == list(s).
> 
> :- instance showable(int)    where [ show(I) = string.string(I) ].
> :- instance showable(string) where [ show(S) = S ].

This part:

> :- func hetlist = list_of_showable.
> hetlist = [ s(123), s("bla") ].         % <-- line 63

... is by me. It isn't part of the example above.


Bye
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