[MLton] HOL's Moscow ML implementation, and pushing MLton to
Daniel C. Wang
Fri, 08 Apr 2005 19:08:09 -0400
I forgot an extra level of indirection... here is some example code.
Assume that listF is always a fully boxed rep.
(i.e)' it's always a null pointer or a pointer to a pair of pointers.
Notice that wrapIntList and wrapRealList are constant time operations.
Shao's approach makes polymorphic/intrerpter code pay a penalty. There is no
polymorphic penalty for monomorphic/host code.
structure List =
datatype ('a,'b) listF =
| Cons of ('a * 'b)
fun length wrap Nil = 0
| length wrap (Cons(_,b)) = 1 + length wrap (wrap b)
fun wrapIntList  = Nil
| wrapIntList (x::xs) = Cons(x,xs)
fun wrapRealList  = Nil
| wrapRealList (x::xs) = Cons(x,xs)
val v1 = length wrapIntList (wrapIntList [1,2,3,4])
val v2 = length wrapRealList (wrapIntList [1.0,2.0,3.0,4.0])
Stephen Weeks wrote:
>>>Sure. MLton represents a Real64.real list using 12 bytes per list
>>>element, while it represents an Int32.int list using 8 bytes per list
>>In this case the universal rep is just a pair of pointers one to the head
>>and one to the tail... i.e. you can build that in constant time!
> That is the universal representation of "real * real list", not "real
> list". It's the recursive type that causes problems.
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