Re: [PATCH] Support the mksh's ${|func;} substitution

[Bart Schaefer <schaefer@brasslantern.com>]

On Wed, Sep 11, 2019 at 7:07 PM Sebastian Gniazdowski
<sgniazdowski@gmail.com> wrote:
>
> On Thu, 12 Sep 2019 at 03:03, Bart Schaefer <schaefer@brasslantern.com> wrote:
> >
> > In an (e) glob, REPLY is set to each possible file name in turn, but
> > $reply can provide multiple names to the final result.
>
> array( "a" "b c" "d" )
> func() { reply=( ${=REPLY} ); }
> array=( ${(x^func^)array} )
>
> and it would result in FOUR array elements, not three. [...]
> I think that in order to
> allow contraction of the result, the (x) flag could use only reply,
> without REPLY as opposed to the (e), unless we do that reply being
> just set invalidates REPLY and allows the empty result.

Hm, perhaps you're still confused about something.  The value of
$REPLY means nothing after the code has run -- it's strictly an input.
$reply is the only output.  So if we were to do as I'm suggesting,

array( "a" "b c" "d" )
func() {
  if (( ${#${=REPLY}} > 1 ))
  then reply=()
  else reply=( $REPLY )
  fi
}
array=( ${(x^func^)array} )

would result in two elements ("a" "d").

Oh, I've forgotten an important bit -- the return value of the code
matters as well.  The full semantics is:
1. on entry, REPLY is set to one element and reply is unset
2. If the code returns nonzero (false, failure) then the result is the
empty array
   (so the corresponding element is removed from the input set)
3. else if reply has become set, that array is used (even if empty)
   (so the corresponding element may become zero, one, or more elements)
4. else if REPLY is set, the value of REPLY is used
   (so the corresponding element changes, possibly to an empty string)
5. else the original element is unchanged

> > Whether the syntax ${(x+func)...} would call "func" once for each
> > array element (again by analogy to glob (e+func))
>
> Why only one + in the examples? (I've tried this syntax with (e), it
> doesn't seem to support it).

Oops, I've typo'd.  as a glob flag, (+func) is (e:func:), you don't
use (e+).  I don't think we can get away with using a bare leading "+"
like that in parameter flags.

Here are examples globbing in my zsh source (gmail is probably going
to line wrap some of this, sorry):

% i=0; echo *(oNe:'REPLY=$((++i))':)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
% echo *(e:'() return 1':)
zsh: no matches found: *(e:() return 1:)
% func() { if (( $#REPLY > 4 )); then REPLY=; fi }
% echo *(oNP:,:+func)
, Misc ,  ,  ,  ,  , Test , Util ,  ,  ,  ,  ,  ,  ,  ,  , Etc ,  ,  ,
 ,  ,  ,  ,  ,  ,  , NEWS ,  ,  ,  ,  ,  ,  ,  ,  , Doc ,  ,  , zsh ,
,  ,  , Src
% func() { if (( $#REPLY > 4 )); then reply=(); fi }
% echo *(+func)
Doc Etc Misc NEWS Src Test Util zsh