[plt-scheme] Recursive types and their specification

From: Noel Welsh (noelwelsh at yahoo.com)
Date: Tue Aug 9 11:44:52 EDT 2005

--- Robby Findler <robby at cs.uchicago.edu> wrote:

> Did you try using a datatype to do that?

Nope.  Being a faithful student of HtDP I decorate my
Scheme programs with type declarations in the comments, so
this question arose from Scheme programming, not <your
favourite statically typed FPL>.  I couldn't see a way to
write down the type without going introducing extra

--- Matthew Flatt <mflatt at cs.utah.edu> wrote:

> Yes. As your subject line says, the problem is a
> equi-recursive function type
>   mu x . () -> (action * x)
> which is not in the type system.

Thanks.  This is interesting.  Had I the time, I'd read
more about this (Google turns up some interesting hits); as
it is, back to Pacman.


Email: noelwelsh <at> yahoo <dot> com   noel <at> untyped <dot> com
AIM: noelhwelsh
Blogs: http://monospaced.blogspot.com/  http://www.untyped.com/untyping/

Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 

Posted on the users mailing list.