On Tuesday 08 Nov 2011 16:35:40 Ralf Hemmecke wrote:
> > Monad(String,List)
>
> Can you give an argument why a compiler would accept your expression,
> but reject
>
> Monad(String, Map)
>
> or
>
> Monad(String, Fraction)
>
> ?
> In SPAD such things are decided at compile time, not runtime.
>
> Ralf
So what you are saying is that if we compiled:
Monad(A: Type, M: partialType): Category == with {
unit: A -> M o A
mult: M o M o A -> M o A
}
and then used:
Monad(String, Fraction)
It would not be detected as an error at that stage because it would
not do the substiutions inside Monad and see that 'Fraction String' is
not a valid type. Perhaps this is another difference between SPAD and
Haskell?
In that case I guess it would need some extra syntax to enforce this
better, perhaps a symbol that means 'can-be-applied-to' like this:
Monad(M: partialType can-be-applied-to A or M): Category == with {
unit: A -> M o A
mult: M o M o A -> M o A
}
Martin
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