In fact in many languages - including every version of Lisp before Scheme and Perl before my was introduced in Perl 5 - dynamic scope was routinely used for what we now tell people to use lexical scope for.

That would be a grave mistake. If that is true, then I can certainly see why you would be hesitant about the use of dynamic scope; it is clearly inappropriate for avoiding namespace clashes. That wouldn't work very well at all; there would be all sorts of hard-to-debug problems if it were used for that. However, that doesn't mean dynamic scope isn't useful, or even that it's less useful than lexical scope; it only means it's not useful for the same kinds of things.

And there are times when you really do want dynamic scope. But those are few and far between.

I can't agree with that. When you understand dynamic scope properly (i.e., are using it for what it's good for, not as some kind of warped substitute for lexical scope), it's very useful indeed.

If you need to simulate lexical scope in a language that doesn't support it directly, the right way to do that is by naming convention (i.e., name your lexical variables starting with the name of the package (and possibly routine) that contains them), not by misusing dynamic scope. But it's also not appropriate to try to use lexical scope as a substitute for dynamic scope; that would be at least as hideously inappropriate, if it could even be made to work at all.

And no, most of the time you aren't going to be dynamically scoping lots and lots of variables. But the ones that you do need to scope that way, you need to scope that way. As you point out, trying to work around a lack of it is nightmarish. Yeah, it can be done -- in the same sense that recursion can be done in languages like line number BASIC that don't support passing parameters to subroutines. (I did this once. It was kinda fun, actually, in a perverse sort of way. I used a set of parallel arrays to simulate a stack, which I pushed my values onto before GOSUB (to save them) and then popped them off of after the routine RETURNed. It was messy, though, and fun only as an exercise, and I don't want to do it again.) 

for(unpack("C*",'GGGG?GGGG?O__\?WccW?{GCw?Wcc{?Wcc~?Wcc{?~cc'
.'W?')){$j=$_-63;++$a;for$p(0..7){$h[$p][$a]=$j%2;$j/=2}}for$
p(0..7){for$a(1..45){$_=($h[$p-1][$a])?'#':' ';print}print$/}

[download]

In reply to Re: Implementing (elisp-like) buffers in Perl 6: how to do buffer-localisation of arbitrary package variables? by jonadab
in thread Implementing (elisp-like) buffers in Perl 6: how to do buffer-localisation of arbitrary package variables? by jonadab

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.