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Re: question on elisp best practive


From: Aemon
Subject: Re: question on elisp best practive
Date: Fri, 12 Oct 2007 00:51:08 -0000
User-agent: G2/1.0

On Oct 10, 2:22 am, Barry Margolin <address@hidden> wrote:
> In article <address@hidden>,
>
>
>
>  Aemon <address@hidden> wrote:
> > Hi all,
>
> > I've got a lot of code that traverses trees and does something at
> > every node. I'd like to abstract the traversal part of the code, and
> > just pass in the bit that does the action. Something like:
>
> > (defun visit-each (tree func depth)
> >   (funcall func tree depth)
> >   (dolist (ea (tree-children tree))
> >     (visit-each ea (+ 1 depth))))
>
> > This seems to work pretty well, called like so:
>
> > (visit-each my-tree
> >        (lambda (subtree depth)
> >          (message "%s %s" subtree depth)))
>
> > However, as it's not a closure I'm passing in, I would get into
> > trouble if I tried:
>
> > (visit-each my-tree
> >        (let ((depth "my depth"))
> >          (lambda (subtree)
> >            (message "%s %s" subtree depth))))
>
> > Elisp's dynamic scope would cause my local binding of 'depth' -> "my
> > depth" to always be shadowed.
>
> Does it work if you use lexical-let instead of let?
>
> --
> Barry Margolin, address@hidden
> Arlington, MA
> *** PLEASE post questions in newsgroups, not directly to me ***
> *** PLEASE don't copy me on replies, I'll read them in the group ***

Wow - I was not aware of that :)
That seems to work pretty well. I guess it's probably well understood
that lambdas passed to library functions should lexical-let ( or be
careful what variables they reference) ?

Thanks!
Aemon



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