type of 'id'?

[John Nowak]

In Cat, 'id' is assigned the type 'a -> a'. I'm curious why it isn't
'A -> A'. In other words, why does 'id' require there be anything on
the stack? I would've assumed the meaning of 'id' to be "returns the
stack unchanged" rather than "returns the top value of the stack
unchanged".

- John

[Christopher Diggins]

Hi John,

The "id" operation is used just to simplify certain type signatures.
In reality it doesn't vary from the the "noop" operation:

define noop : ('A -> 'A) { }

- Christopher