Default values for key-value macros

Default values for key-value macros

[noib3 via ntg-context]

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The way I've been defining key-value macros is to first pass them to Lua,
handle the parsing there thanks to `utilities.parsers.settings_to_hash` and
then assign the resulting Lua table to ConTeXt variables.

This worked fine up to now, but I'm having problems with the following MWE:

```
\def\style#1[#2] {
  \ctxlua{userdata.style([==[#2]==])}
  \placestyle
}

\startluacode
  userdata = userdata or {}

  userdata.style = function(keyvals)
    local style = {
      color = nil,
      text = nil,
    }
    args = utilities.parsers.settings_to_hash(keyvals)
    for k, v in pairs(args) do
      style[k] = v
    end
    context.setvariables({'style'}, style)
  end
\stopluacode

\define\placestyle{
  \doiftext
    {\getvariable{style}{text}}
    {\color[\getvariable{style}{color}]{\getvariable{style}{text}}}
}

\starttext

\style[
  text={Some red text},
  color=red,
]

\style[
  color=blue,
]

\stoptext
```

Here I assign a default value of `nil` to every key, and then check if the
`text` variable is empty before printing it. I would expect the second
macro not to print anything since its `text` should be nil, instead both
macros print 'Some red text', the first one in red and the second one in
blue.

I have attached a screenshot of the output.

What am I doing wrong?

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Re: Default values for key-value macros

[Hans Hagen via ntg-context]

On 10/10/2021 2:01 PM, noib3 via ntg-context wrote:
> The way I've been defining key-value macros is to first pass them to 
> Lua, handle the parsing there thanks to 
> `utilities.parsers.settings_to_hash` and then assign the resulting Lua 
> table to ConTeXt variables.
> 
> This worked fine up to now, but I'm having problems with the following MWE:
> 
> ```
> \def\style#1[#2] {
>    \ctxlua{userdata.style([==[#2]==])}
>    \placestyle
> }

here you overload a core macro

> \startluacode
>    userdata = userdata or {}
> 
>    userdata.style = function(keyvals)
>      local style = {
>        color = nil,
>        text = nil,
>      }
>      args = utilities.parsers.settings_to_hash(keyvals)

use "local args" here ^

>      for k, v in pairs(args) do
>        style[k] = v
>      end
>      context.setvariables({'style'}, style)
>    end
> \stopluacode
> 
> \define\placestyle{
>    \doiftext
>      {\getvariable{style}{text}}
>      {\color[\getvariable{style}{color}]{\getvariable{style}{text}}}
> }
> 
> \starttext
> 
> \style[
>    text={Some red text},
>    color=red,
> ]
> 
> \style[
>    color=blue,
> ]
> 
> \stoptext
> ```
> 
> Here I assign a default value of `nil` to every key, and then check if 
> the `text` variable is empty before printing it. I would expect the 
> second macro not to print anything since its `text` should be nil, 
> instead both macros print 'Some red text', the first one in red and the 
> second one in blue.

context.setvariables

like any setting, it accumulates unless you group

> I have attached a screenshot of the output.
> 
> What am I doing wrong?

     local style = {
       color = "",
       text  = "",
     }

or you can go fancy with:

\startluacode
interfaces.implement {
     name      = "MyStyle",
     public    = true,
     protected = true,
     arguments = "hash",
     actions   = function(a)
         if a.text and a.text ~= ""  then
             if a.color and a.color ~= "" then
                 context.color( { a.color }, a.text)
             else
                 context(a.text)
             end
         end
     end
}
\stopluacode

\MyStyle[
   text={Some blue text},
   color=blue,
]

\MyStyle[
   color=blue,
]

\MyStyle[
   text={test \em test},
]



-----------------------------------------------------------------
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___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________