On Fri, Nov 29, 2002 at 04:52:03PM -0000, Nicolas Cannasse wrote:
> Of course the ML type system relies on type inference and need do choose the
> "best available" type but what if we enrich the type system with an "OR"
> operator ? Then if (+) is overloaded on floats, you'll get :
> 
> f :  int -> int OR float -> float
> or something like a type constraint :   f : 'a -> 'a where 'a in [int;float]
> 
> This approach seems trivial to me, but I really can understand that this
> require a lot of addins in the typing algorithms & theory. BTW, does one of
> the upper approach has already been discussed ? any paper on it ? any
> countersample that will make me feel stupid ? :)

The problem is what *assembly code* should be generated for function f?
Code to add 2 integers or code to add 2 floats? Hmm.. we'll have a
problem then. Or maybe both? And choose versions of f based on type it
is applied to? But then consider:

let f x1 x2 ... xn = ((x1 + x1), (x2 + x2), ..., (xn + xn))

you need to generate 2^n versions of f. We're getting to ugly things
like C++ templates here.

There is third answer: generate code that checks if it's passed int or
float. But this has very significant perfomance impact.

-- 
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