Re: higher-order functors

Dave Herman wrote:

> At this point I was stabbing in the dark, but I tried moving the 
> where-clause instead to the declaration of MK_COROUTINE:
> 
>      funsig MK_COROUTINE (type result) = COROUTINE
>          where type result = result
> 
> But then I got the compiler error:
> 
>      Error: Compiler bug: LtyExtern: wrong TCs in tc_select
> 
>      I
> 

As another data-point, I just encountered the same error while 
attempting to use higher-order functors.  In my case, the
example below compiles fine if I remove the definition of "add'". 
Alternately, I discovered that rewriting it as

	fun add' (x, b) = add (b, x)

also compiles fine.  eta-reducing the definition below to

	val add' = add o swap

doesn't fix the problem.  I'm using 110.62, with patches to the parser, 
but the problem also occurs when I tried an unpatched build of 110.54.


functor Bag (functor Map(K : ORD_KEY) : ORD_MAP) (K : ORD_KEY) = struct

   structure Key = K
   structure BM : ORD_MAP = Map (K)

   type item = BM.Key.ord_key
   type bag = word BM.map
   type t = bag

   val empty : bag = BM.empty
   fun singleton (x : item) = BM.singleton (x, 0w1)

   fun add (b : bag, x : item) =
       (case BM.find (b, x)
          of SOME n => BM.insert (b, x, n + 0w1 )
           | NONE => BM.insert (b, x, 0w1))

   fun swap (x, y) = (y, x)

   fun add' x = (add o swap) x

   (* ... other operations not yet implemented ... *)

end


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