[m-dev.] require_tail_recursion(name/arity, [none])

[Julien Fischer]

Hi Zoltan,

Your original proposal is fine; I didn't read the mail subject
properly and misunderstood
what you are trying to do.

Julien.

On Fri, 5 Jun 2026 at 16:21, Zoltan Somogyi <zoltan.somogyi at runbox.com> wrote:
>
>
>
> On Fri, 5 Jun 2026 15:35:52 +1000, Julien Fischer <jfischer at opturion.com> wrote:
> > On Fri, 5 Jun 2026 at 14:47, Zoltan Somogyi <zoltan.somogyi at runbox.com> wrote:
> > > Would anyone object if I replaced this syntax with a new pragma
> > > named suppress_tail_recursion(name/arity)? It would make documenting it
> > > significantly easier. (The internal representation already corresponds to the
> > > proposed new syntax, because it is clearer.)
> >
> > Is that not conflating two things? The requirement that a predicate
> > uses constant
> > stack space with warning suppression about a lack of tail recursion.
>
> I guess suppress_non_tail_recursion_{diagnostic,warning} would be
> more descriptive names. Would something like that make you happy?
>
> However, other than that possible misunderstanding, there is no conflation here:
> requiring constant stack space IS requiring tail recursion, and the only effect
> of a requirement not being met is a diagnostic. The pragma's name implicitly says
> it is asking for a diagnostic if the requirement is not met. Using that same name
> to FORBID the diagnostic seems counterintuitive.
>
> The existing require_tail_recursion pragma controls diagnostics in one of two ways:
>
> - in the usual case where --warn-non-tail-recursion is not set, it ENABLES diagnostics
>   about non-tail recursion for a pred or func, and
>
> - in the case where --warn-non-tail-recursion IS set, it can DISABLE those very same
>   diagnostics for a pred or func.
>
> People can now do the latter by specifying the option "none". This option is completely
> different from all the other options, and is also incompatable with all of them.
> Instead of trying to describe this clusterfck in the manual, I would prefer to
> simply describe a simple pragma that disables these diagnostics for a pred or func
> in the presence of --warn-non-tail-recursion.
>
> I am not proposing any change in semantics, only in syntax.
>
> > The name require_tail_recursion fits with the other assertion-like constructs
> > in the language (e.g. require_det, require_feature_set).
>
> Yes, but the whole point of the proposed new pragma is to NOT require something.
> Including "require" in the name of such a construct seems ... counterproductive.
>
> Zoltan.