2013/8/20 David Pirotte <[email protected]>
> Hello,
>
> > It seems following is invalid:
> >
> > (let ((a 2))
> > (define (foo x) (+ a x)))
> >
> > I prefer to reduce scope of variable as much as possible, so
> > I find this restriction unconvinent. Is is part of standard or technical
> > limitation? Is it any workaround?
>
The Scheme's idiomatic way to achieve the effect that you
probably want would be
(define foo #f)
(let ((a 2))
(set! foo (lambda (x) (+ a x))))
Although it allows to achieve the desired effect, it doesn't
express the programmer's intention quite clearly.
If you're interested, I recently wrote a macro that would
allow to get the same in a IMHO slightly more elegant way, i.e.
(publish
(define (foo x) (+ a x))
where
(define a 2))
The macro's definition (procedural) follows.
Regards.
=============================
(define-macro (publish . definitions)
(define (interface-name interface)
(match interface
((head . tail)
(interface-name head))
((? symbol? name)
name)))
(let-values (((public-definitions where&private-definitions)
(split-before (equals? 'where) definitions)))
`(begin ,@(map (match-lambda
((define-variant interface . body)
`(define ,(interface-name interface) #f)))
public-definitions)
(let ()
,@(match where&private-definitions
(('where . private-definitions)
private-definitions)
(() '()))
,@(map (match-lambda
((define-variant interface . body)
(let ((name (interface-name interface)))
`(set! ,name
(let ()
(,define-variant ,interface . ,body)
,name)))))
public-definitions)))))
