Re: [stack] Type for row based languages

One more thing I should've mentioned. You state that your type system  
is compositional. I should note that you can get this quite easy by  
extending HM with row types and omitting any equivalent to let  
polymorphism. For example, 'dup apply' would fail to type:

     A b -> A b b
            C   (C -> D) -> D

     A (C -> D) -> A (C -> D) (C -> D)
                   C          (C -> D) -> D

     -- error: C occurs in A (C -> D)

Luckily (for some definition of "luck"), something like '[id] dup  
apply' would fail as well:

     A -> A (B -> B)
          C d        -> C d d

     A -> A (B -> B)
          C (B -> B) -> C (B -> B) (B -> B)

     A -> A (B -> B)
          A (B -> B) -> A (B -> B) (B -> B)

     A -> A (B -> B) (B -> B)

     A -> A (B -> B) (B -> B)
          C          (C -> D) -> D

     A -> A (D -> D) (D -> D)
          C          (C -> D) -> D

     A -> A (C -> C) (C -> C)
          C          (C -> C) -> C

     -- error: C occurs in A (C -> C)

For all expressions that do yield valid types, the order in which you  
infer the type does not matter.

Apologies if I'm stating the obvious.

- John