On Monday, November 19, 2001, at 10:32 AM, Krishnaswami, Neel wrote:

>
> A functor is compiled to what is essentially a function that
> takes a record as an argument (the module it receives as an
> argument), and returns a record of functions and values. So
> code generation happens only once for each functor, and each
> functor application takes a very small amount of memory at
> link time.
>

Which of course is a problem at the "small-scale". For example I would 
like to develop a functor that is generic over the representation of 
reals (float32_elt, float64_elt, fixed_point, etc.). But now if I 
instantiate it for float64_elt and do arithmetic over float64_elt even 
simple operations will be looked-up at run-time leading to a terrible 
performance loss.

Ideally I would prefer it if the compiler allowed the programmer to 
decide which functor applications lead to compile-time code generation 
and which are through dictionary-passing.

For example, in Clean (which has type classes not functors of course), 
instants of basic types be prevented from using dictionary passing. Not 
sure what happens in haskell though...

--shiv--
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