Re: Temporary variables in make .for loops

On Fri, Nov 11, 2022 at 4:56 PM Tijl Coosemans <tijl@freebsd.org> wrote:
>
> On Fri, 11 Nov 2022 15:41:51 +0300 Gleb Popov <arrowd@freebsd.org> wrote:
> > Hello fellow porters.
> >
> > My variable modifiers are growing and become too incomprehensible, so
> > here is the question I wanted to ask long ago:
> >
> > How do I make and use a temporary variable in the .for loop?
> >
> > This is what I have in Mk/Uses/cabal.mk:
> >
> > .  for package in ${_use_cabal}
> > _PKG_GROUP=        ${package:C/[\.-]//g}
> >
> > MASTER_SITES+=    https://hackage.haskell.org/package/:${package:C/[\.-]//g}
> > .  endfor
> >
> > I'd like to write ${_PKG_GROUP} instead of repeating that regexp
> > incantation, but due to specifics of .for operation it doesn't work.
> > Using := with _PKG_GROUP also doesn't fix the problem.
> >
> > Now I need to add another regexp substitution to every expression
> > inside this loop and it'll become even less readable than before.
> >
> > Is there a clean solution to this problem?
>
> You could use a nested .for loop:
>
> .  for package in ${_use_cabal}
> .    for pkg_group pkg_norev rev in \
>         ${package:C/[.-]//g} ${packa...} ${packa...}
>
> You can drop the backslash by the way.

That's a really neat trick, thanks!