Re: Loops (was Re: do { quit; } else { })

On 2025-04-23, bart <bc@freeuk.com> wrote:

On 23/04/2025 16:31, David Brown wrote:

On 22/04/2025 22:03, bart wrote:

>

Too few levels of functions and/or macros (there is no semantic
difference between macros and functions in this matter)

>
There is a great deal of difference. Functions tend to be well-formed in
their inputs and outputs.
>
Macros take some abitrary blocks of syntax and return another arbitrary
block of syntax:
>
     #define INDEX(a, b, y) a y b
     INDEX(a, i, [) ];

While that's terrible, I've never seen anything like it in the wild.

Macros which open a brace, relying on the invocation of a paired
macro to close it, are reasonably common.

The macro we had been discussing whereby the for (..) part of
a loop is also an example of something which generates a syntactic
fragment, which must be completed by something which follows
the macro, namely a statement.

Speaking purely in terms of formal syntqx, this is exactly what is going
on in your example with the completing closing bracket. In that
situation, it gives us a useful technique whose use is clear.

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