Re: Why is there no `until' in elisp?

[Paul Eggert]

On 10/17/18 2:46 AM, Yuri Khan wrote:
> + Pascal has ‘repeat’/‘until’ (a termination post-condition loop), and
> it was my first association for the name ‘until’.

Pascal did it right, for a reason I haven't seen mentioned in this 
thread. The natural tendency when reading a conditional is to assume 
that the condition will be true in the code that immediately follows the 
text of the condition. This works for (if C S) and (while C S), and it 
also works for Pascal's 'repeat S1 until C; S2' where C is true just 
before S2 is executed. It does not work for the confusing C syntax 'do 
S1 while (C); S2' where C is false just before S2 is executed. It also 
does not work for the proposed Elisp syntax (until C S), where C would 
be false just before S is executed. Because of this elementary 
psychological principle, the Elisp syntax for the proposed loop 
construct should *not* be (until C S).