Re: Proposed feature: die on compile with undefined functions

On Thu, 29 Jan 2026, 11:52 Philippe Bruhat (BooK), <[email protected]>
wrote:

> On Wed, Jan 28, 2026 at 11:59:47AM -0600, David Condon wrote:
> >
> > *1. Here is a problem*
> > Scripts that have undeclared subroutines will run, even though the
> > subroutines are not declared/loaded/whatever:
> >
> > There are no syntax changes.  The only change is that undefined
> subroutines
> > would be treated the same way that undefined scalars are treated.
>
> s/undefined scalares/undeclared scalars/
>
> > I want perl to check for the undefined function max before running the
> > script, similarly to the way that this 1-line script:
>
> > *4. Here are potential problems*
> >
> > I am unaware of any.  I just want something that will happen anyway to
> > happen sooner to save time.  This change *shouldn't *be buggy.
>
> The problem is see is that it's extremely hard to detect if a function
>

Indeed, "halting problem" hard.

will be defined by the time Perl tries to call it:
>
>     use v5.42;
>     require List::Util;
>     List::Util->import("max");
>     say max( 1..10, -1..7);
>
> All of those lines happens at run time, and max is available by the time
> it's called. At the end of compilation, though, max is not defined


And while a super strict mode could require forward declarations for this
exact case there are others where we document that forward references to
fully qualified subs should  work.

Yves