[mercury-users] "some" and existential types

[Robert Ernst Johann JESCHOFNIK]

On Sun, 3 Oct 1999, Fergus Henderson wrote:

> There's an easy solution here: just declare `anything' to be an
> instance of `printable':
> 
> 	:- instance printable(anything) where [
> 		pred(print/3) is print_anything
> 	].
> 
> 	:- pred print_anything(anything::in, io__state::di, io__state::uo)
> 		is det.
> 	print_anything(thing(X)) --> print(X).
> 
> Then you can write `print_anythings(Xs) --> list__foldl(print, Xs)'
> and it should work just fine.

should this be "print_anythings(Xs) --> list__foldl(print_anything, Xs)."?
I'm still rather iffy on typeclasses and the like..


rob
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