Re: Equivalent of Vim's has("feature")?

["Benjamin R. Haskell" <zsh@xxxxxxxxxx>]

On Mon, 22 Nov 2010, Peter Stephenson wrote:

> On Mon, 22 Nov 2010 12:12:51 -0500 (EST) "Benjamin R. Haskell" wrote:
> > For commands and widgets I've found the following to work well:
> >
> > (( $+commands[screen] )) && # do something with screen
> >
> > (( $+widgets[history-incremental-pattern-search-backward] )) \
> > && bindkey "^R" history-incremental-pattern-search-backward
> >
> > But, 1) I can't seem to rediscover the documentation for those 
> > arrays,
>
> Look at the documentation for the zsh/parameter module in zshmodules.

Thanks.  Didn't realize these weren't standard (for some value of 
"standard").


> > and 2) Is there such an array for things that are more inbuilt?  In 
> > particular, I'm looking for a test that the ':A' history modifier 
> > exists.
>
> If you haven't recorded the version when it first appeared so you can 
> use the is-at-least function, which is the usual way (as long as you 
> do it as soon as the feature appears it's painless),

Is there any support for ZSH_PATCHLEVEL in is-at-least?  :a and :A were 
added in ZSH_VERSION=4.3.10(-dev-1?) ZSH_PATCHLEVEL=1.4618.


> you have to attempt to make use of the feature and record the result.
>
> integer history_A
> ( : ${PATH:A} ) 2>/dev/null  &&  history_A=1

Both of these seem slippery-slopy.  (Easy for one feature, but 
increasingly annoying as more tests are needed.  Also, if a given 
feature takes non-trivial time to test.).  Nonetheless, I guess I don't 
have some easy-peasy way to add the feature detection to the case 
statement in Src/hist.c and a new parameter in Src/Modules/parameter.c 
(<-- note to self in the unlikely even I get back to this), so I'll 
retreat with:

( : ${${:-/}:A} ) 2>/dev/null && has_A=true
...
(( $+has_A )) && # use it

which works fine for this case.

--
Thanks,
Ben