[bitc-dev] Type compatibility at application

[Jonathan S. Shapiro]

> OK. Are you thinking of a case like:
> 
> (define (f x:(vector 'a) #t)
> 
> (define vec1:(vector int32)  (vector 1 2 3))
> (define vec2:(vector (mutable int32)) (vector 1 2 3 ))
> 
> (define vecApp
>     (begin
> 	(f vec1)
> 	(f vec2)
> )

Yes. I am thinking of exactly this. And here is the weird part: if F can
operate correctly on (vector (non-mutable T)), then it will operate
equally correctly on (vector (mutable T)). There is a subtyping thing
going on here. The complication is contravariance.

> The solution may be an optimization that the polyinstantiator can 
> perform -- if there are two instantiations that only differ in the 
> mutability of arguments, only one of them needs to be emitted during 
> code generation.

Maybe. But the difference in mutability cannot be based simply on
shallow analysis.

This is definitely an issue for later, not for now.


shap