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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: Named options/enumerations (Was re: Defining \bool_case:nn)
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On 09/07/2013 04:27, Joel C. Salomon wrote:
>>> This use of named options feels like it should be reasonably common i=
n
>>> user-facing code, but Expl3 doesn=92t have an obvious way of managing
> this.
>>>
>>>     \keys_define:nn { jcsfonts }
>>>       { font .choice_code:n =3D \tl_gset:NV \g_jcsfonts_option_tl
>>> \l_keys_choice_tl }
>>>
>>>     \str_case:Vnn \g_jcsfonts_option_tl
>>>       { { cmodern } {} % Computer Modern is LaTeX default
>>>         { kpfonts } { \RequirePackage{kpfonts} }
>>>       } { \msg_error=85 }
>>
>> What about
>>
>>     \keys_define:nn { jcsfonts }
>>       {
>>         font .choice: ,
>>         font / cmodern .code:n =3D { } ,
>>         font / kpfonts .code:n =3D { \RequirePackage{kpfonts} } ,
>>       }
>>
>> This will trigger a "key-choice-unknown" error upon encountering an
>> unknown choice (well, right now the message is not defined... that'll
>> be fixed).  Maybe we could add a feature to allow arbitrary code for
>> unknown choices.
>=20
> The code in the various options is more than a single line =97 about te=
n
> lines per option, actually, and it seems messy to intertwine option
> processing with option execution like that.

What's wrong with

  \keys_define:nn { jcsfonts }
    {
      font .choice: ,
      font / cmodern .code:n =3D { } ,
      font / kpfonts .code:n =3D  { \jcsfonts_kpfonts: } ,
      ...
      font / unknown .code:n =3D { \jcsfonts_load_unknown:n {#1} }
    }

or similar, i.e. placing the 'payload' in support functions (may be some
are can be combined with different args: no idea what the real code is!).
--=20
Joseph Wright