Dynamic Binding

[James J. Besemer]

Tim Peters wrote:

> [Tim]
> > It seems this would have been a surprise to McCarthy <wink>:
> >
> >     http://www-formal.stanford.edu/jmc/history/lisp/node4.html

> [James J. Besemer]
> > I disagree with your interpretation.
>
> I take it you didn't follow the link and read the referenced paragraph.

No, I must confess I did not.  I started to and then got drawn into doing some
real work for a couple days.  Also, it looked familiar and I was thinking that
maybe I had read it long ago.

When finally I sat back down to reply, my objective was merely to establish that
dynamic scoping originally was SOP in Lisp.  From that perspective, the quote
does speak for itself.  I actually thought you cited the quote in contradiction
of my premise and I said I disagreed because it clearly does not.

But actually, in a way, you were agreeing with me, right?  ;o)  And the quote
does provide additional fodder.

So I was wrong to disagree with you because you were agreeing with me, right?
:o)

Mistakes like this can happen in "heated agreement."

Please excuse my misunderstanding.

> > Rather he is saying that the implementation DID use dynamic "scoping,"
> > that it worked just fine in most circumstances and that when people
> > encountered a situation where "lexical scoping" would help McCarthy
> > regarded their "difficulty" simply to be a bug.
>
> I'll just finish the sentence I partially quoted:
>
>      I must confess that I regarded this difficulty as just a bug and
>      expressed confidence that Steve Russell would soon fix it.

Clarifies the ambiguity about who's bug it was.

> The differences between
> lexical and dynamic scoping weren't clearly understood at the time.  Yes, it
> used dynamic scoping, but the full implications of that implementation
> choice weren't understood in advance, and some came as unwelcome surprises.

I think we're in complete agreement here.

As I said elsewhere in my previous post, I think dynamic scoping a natural
progression that many language designers go through.  The associated problems
are fairly subtle and complex.

> Reading the paper remains a recommended alternative to presumption <wink>.

It does look worthwhile.  I'll definitely make a point of reading it.

Thanks for the history pointer, the clarifications, an interesting discussion
generally and your patience.

Regards

--jb

--
James J. Besemer  503-280-0838 voice
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