Question about alloca() and alternative to using stack in an implementation

[Dan Pop]

It is an assumption. That doesn't prevent it from being a correct
assumption, and therefore also a fact.

It is an implicit premise for your statement about the non-portability
of VLAs, which would have been clearer if you had stated it
explicitly.

Anyone reasonably familiar with C89 should be aware that there are no
such things as VLAs in the language. And a discussion about alloca is
not supposed to be for green newbie consumption. So, why should I treat
my target audience as a bunch of ignorants?

Dan