Re: [Chicken-users] Binding identifiers with set!

[felix]

On 13 Oct 2003 09:24:26 +1300, Bruce Hoult <address@hidden> wrote:

> The thing that I dislike *more* is the (documented) way that Chicken
> makes "define", other than at the start of a lambda-or let-body,
> exactly equivalent to set!.  i.e. per r5rs a define at the start of a
> body is exactly the same as a "let" (and several are the same as a
> "letrec") and creates a local lexical binding with the rest of the body
> inside the "let", but if you put so much as a debug output statement
> before one of the defines then it suddenly modifies (or, per your
> complaint, creates!) a toplevel variable instead of a local binding. This 
> has caught me out more than once.
>
> My own preference would be for *every* non-toplevel "define" being the
> same as a "let" having the rest of the body as its scope.  Which means
> that a series of "defines" is effectively a "let*".
>
> This would be in line with the way that local bindings work in Dylan or
> C++ or almost any other modern language. Unfortunately it is in conflict
> with r5rs at the start of a lambda-or let-body because r5rs requires a
> sequence of "define"s to be "letrec", not "let*"  :-( :-(

Well, you could handle this by treating every sequence of local defintions
as a letrec. So for example

(let (...)
 (define foo 1)
 (define bar 2)
 (print "oink!")
 (define baz 3)
 (define quux 4)
 ...)

would expand into:

(let (...)
 (letrec ([foo 1] [bar 2])
   (print "oink!")
   (letrec ([baz 3] [quux 4])
     ...) ) )

This would be compliant to R5RS (for the first set of definitions).

Would this be useful?


cheers,
felix