[Caml-list] Re: Strange behavior of mutualy recursive definitions

[Jeffrey Scofield <jeffsco@psellos.com>]

rixed@happyleptic.org writes:

> Why 'let rec f = f' is rejected is clear: you cannot type f.

In my thinking, f is typeable with type 'a (fully general type).
I don't think it's untypeable, it just doesn't have a useful type.
It's similar to the type of failwith : string -> 'a, but without
the string.

In Haskell the equivalent definition has useful purposes.
It represents "bottom" (erroneous computation).  In a strict
language you can't have such a value hanging around, seems
like.  So in OCaml you have failwith instead (a lazy version of an
erroneous computation).

So to me it makes sense that it's rejected not on typing but on
other grounds.

It's also worth noting that

    let rec f x = f x

is just a shorthand for

    let rec f = fun x -> f x

This also is typeable with type 'a -> 'b.  Again this isn't a
very useful type, but there's no problem with this value in a strict
language, because the lambda ("fun") essentially makes it lazy.

Jeffrey