Re: Static type-checking with dynamic scoping

It seems to me that one could consider (dynamically bound) free
variables in a procedure to simply be additional parameters to the
procedure. Then standard ML-like type inference could be done.


Not being fluent with ML syntax, I give an example in (dynamically
scoped) Lisp:
(defun f (x)
(y x)) ;; y free, bound dynamically
Here f might taken to have type:
([y: a->b], a) -> b
that is, it takes an argument of type a, a binding of y with type a->b,
and returns a value of type b.


A place where f is used might look like:
(let ((y sub1))
(f 3))
where y has type
int -> int
and f is applied to ([y:int->int], int) which may be unified with the
above, yielding a result of int as well.


Keeping track of all of the current bindings and determining which
onese were relevant in a particular application would certainly
clutter up the type inference, but it shouldn't make it terribly
more difficult.


-Brian Murphy
brm@cs.stanford.edu
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