On Sun, 04 Jun 2000, Koen Claessen wrote:
> You cannot ask a question like this without explaining why
> you are interested in this subject! :-) Just out of
> curiosity... (I think that it is has to do with a recursive
> do-translation, am I right?
Yes, we're working on a new semantics for do, where you'll be able
to bind variables recursively. For instance:
do xs <- Just (1:xs)
return (take 5 xs)
will evaluate to: Just [1,1,1,1,1]
Such recursive bindings are quite useful for a class of problems (and for
a class of monads.)
It turns out that if we allow polymorphic let-bindings, the translation gets
far more complicated. So we're trying to figure out whether restricting
let-generators to be monomorphic is OK.
My apologies for not making this clear in the first posting..
-Levent.
PS. Some more detail for the truly interested: In the recursive-do, one
can stil have polymorphic let-bindings: use the usual <let ... in> form, i.e.
do ...1... --> f is not visible
...2... --> in the first two lines
let f = ....
in do ...3... -+
...4... |> f will be polymorphic here
...5... -+
But, of course, f will not be visible before it's definition (i.e. the first
two lines of the do.) But a let-generator will be visible everywhere:
do .... -+
.... |
let f = ... |> f is visible everywhere (but is monomorphic)
.... |
.... -+
but it will not be polymorphic.
We'll appreciate any comments on this design.. Thanks again,
