Re: Tagged loops (was RE: [PATCH] experimental php-like 'break N' to break acrossmultipleloops)

[Rici Lake <lua@...>]

On 2-Nov-06, at 11:32 AM, Sam Roberts wrote:

> Breaking out of multiple nested loops is useful!
>
>   Knuth - Structured Programming with Goto Statments:
>
>   http://pplab.snu.ac.kr/courses/adv_pl05/papers/p261-knuth.pdf

Nothing like a quick visit to the time machine to get your perspective 
:)

Interesting rereading that article, though, after all these years. It 
struck me forcibly that some ideas tend to re-emerge subliminally, 
although they are often once again repressed.

The loop ... while condition; ... repeat; syntax suggested by Knuth on 
pages 279-280 of that article is pretty similar to (a subset of) the 
syntax suggested by Shivers in the paper I referenced in my post last 
year on the subject, and is almost precisely the implementation I 
provided in the patch which Karel refers to. Here I'm referring to the 
loop primitives, not the labelled break/continue statements, which I 
never particularly liked.

Knuth's comment:

"at first these may seem strange, but probably less strange than the 
while and repeat statements did when we first learned them" (p. 280)

seems to underestimate the reaction to the construct by people who have 
already learned while and repeate statements; certainly, aside from 
sporadic attempts to revive the idea, I know of no mainstream language 
which actually implements the construct, despite Knuth's judgement at 
the bottom of the left hand column on page 280. I presume that most 
programmers don't get beyond the first impression. :)