Re: language design implications for variant records in a pascal-like language

On Fri, 14 Jan 2011 10:50:29 +0000, Martin Rodgers
<mcr@wildcard.demon.co.uk> wrote:


>glen herrmannsfeldt wrote:
>
>> Now, why do some languages have DO ... UNTIL, where others have
>> DO ... WHILE for "test at the end" loops?


          If the test is after the loop, it makes sense. Mind you, I do
not think that putting the test at the end makes sense. I want my
loop control up-front and would rather see
                    until <cond>
                          body
and just know that the body will be executed once for sure. Going
through the body when I know the condition means that I may be able to
desk-check much faster.


>I've always prefered languages that have both. I picked on a specific
>Basic dialect because that was the example that irritated me the most.
>*My* experience of Basic was mainly with another dialect that had
>neither WHILE mor REPEAT - you had to use IF/GOTO or FOR.


          BTDT. I loved it as much as you did.


>BBC Basic was also irritating to me because, unlike the earlier Basic
>implementations that I knew on on micros, the ROM was large enough
>to support both control structures, so why pick just one?


          Microsoft BASIC 5 had WHILE but not UNTIL.


>So I can only guess why the implementers made that choice. To be fair,
>a lot of choices made in Basic implementation of that era seem bizzarre
>to me today. They seemed pretty odd to me at the time, but I learned a
>lot about the pitfalls of language design by studying them, so at least
>they had some value for me. It's a small design space, but that may have
>helped me - at some point, language design comes down to the very
>small details that will matter to programmers and implementers. I can
>recommend this technique to anyone interested in language design - study
>entire families of dialects, their evolution, their implementions, the costs
>and trade-offs made, the context(s) and general family history.


          I always look for the philosophy of a programming language.


>Looking at the subject for this thread, I might suggest starting with the
>Algol family. ;)


Sincerely,


Gene Wirchenko

Return to the comp.compilers page.
Search the comp.compilers archives again.