Re: [stack] Re: Cat article submission to Doctor Dobbs Journal

Briefly, just to give the correct types for functions involving first- 
class stacks:

     infra   :: A {B} (B -> C) -> A {C}
     push    :: A c {B} -> A {B c}
     pull    :: A {B c} -> A c {B}
     nullstk :: A -> A {_}
     stack   :: A -> A {A}
     unstack :: A {B} -> B
     swapstk :: A {B} -> B {A}

swapstk can be defined in terms of the other functions.

- John