Re: [Caml-list] Polymorphic recursion

[skaller <skaller@users.sourceforge.net>]

On Tue, 2007-04-03 at 13:00 -0700, brogoff wrote:
> On Tue, 3 Apr 2007, Till Varoquaux wrote:
> > Therefor, if you wish to use polymorphic recursion (yep you can) you
> > might want to use something where you have to specify the type; this
> > includes records, objects and recursive modules. So this
> >
> > type 'a seq = Unit | Seq of ('a * ('a * 'a)seq)
> >
> > type szRec={f:'a.'a seq -> int};;
> >
> > let size=
> >  let rec s =
> >   {f=function
> >     | Unit -> 0
> >     | Seq(_, b) -> 1 + 2 * s.f b}
> >  in
> >  s.f
> >
> > might be what you where yearning for.
> 
> What I'd be yearning for would be more like
> 
> let rec size : 'a . 'a seq -> int =
>   fun s ->
>     match s with Unit -> 0 | Seq(_,b) -> 1 + 2 * (size b)
> 
> rather than having to use recursive modules or higher rank polymorphism
> of record fields/polymorphic methods.

Why not:

let fun rec size : 'a . 'a seq -> int =
  | Unit -> 0 
  | Seq(_,b) -> 1 + 2 * (size b)

with a nice camlp4 example for people by nicolas.pouillard@gmail.com ? 


-- 
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net