[Haskell] Boxing (Day) Question

[Niklas Sorensson]

> On the whole it looks like you want type variables with kind #.
> There are very good implementation reasons for not allowing this.
> If you had type variables of kind # you could have polymorphic
> functions over unboxed values.  But since the values are unboxed
> they don't have a uniform representation (e.g., a Double# is probably
> twice the size of a Float#).  So polymorphic functions over unboxed
> values are not easy to implement.  (You can imagine implementations
> of them, but none of them are pleasent.)

That reminds me of something that I have wondered about for some
time. Why is there such reluctance to instantiate polymorhic functions
with the types with which they are used? (This isn't done automatically
in complilers right?)

I can imagine that it is akward to delay code generation until all uses
of a function are known, and that in some cases there may be infinitely
many instances needed. But apart from that, what are the reasons
against this implementation technique?

/Niklas