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Date:         Mon, 1 Jul 2013 18:30:29 -0400
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From: "Joel C. Salomon" <joelcsalomon@GMAIL.COM>
Subject: Named options/enumerations (Was re: Defining \bool_case:nn)
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A moment ago, I wrote:
> I=E2=80=99ve invited A. Ellett (the fellow who requested \bool_case on Te=
X.SE)
> to join this thread and explain, but my guess would be that he's got a
> group of booleans, only one of which is supposed to be set at any
> given time: a selection from a set of mutually-exclusive options, for
> example.


This use of named options feels like it should be reasonably common in
user-facing code, but Expl3 doesn=E2=80=99t have an obvious way of managing=
 this.

I recently asked =E2=80=9CCan I refer to key value in general code?=E2=80=
=9D (
http://tex.stackexchange.com/q/120258/2966). My initial thought (somewhat
bizarre, I=E2=80=99ll admit) was to save the option is a quark, set equal t=
o one of
a group of quarks.

Enrico pointed me in the direction of string comparisons, and I=E2=80=99ve =
moved to
using code like 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=E2=80=A6 }

This works, but does not feel entirely satisfactory. Given my C background,
I=E2=80=99m tempted to write an enum package, loosely wrapping l3int, to be=
 used
something like this:

    \enum_case:Vnn \g_jcsfonts_option_enum
      { \c_jcsfonts_cmodern_enum {}
        \c_jcsfonts_kpfonts_enum { \RequirePackage{kpfonts} }
      } { \msg_error=E2=80=A6 }

It=E2=80=99s too early for anything to be idiomatic LaTeX3, but what should
*become* idiomatic?

=E2=80=94Joel

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<div dir=3D"ltr">A moment ago, I wrote:<br>&gt; I=E2=80=99ve invited A. Ell=
ett (the fellow who requested \bool_case on TeX.SE)<br>&gt; to join this th=
read and explain, but my guess would be that he&#39;s got a<br>&gt; group o=
f booleans, only one of which is supposed to be set at any<br>
&gt; given time: a selection from a set of mutually-exclusive options, for<=
br>&gt; example.<br><br><br>This use of named options feels like it should =
be reasonably common in user-facing code, but Expl3 doesn=E2=80=99t have an=
 obvious way of managing this.<div>
<br></div><div>I recently asked =E2=80=9CCan I refer to key value in genera=
l code?=E2=80=9D (<a href=3D"http://tex.stackexchange.com/q/120258/2966">ht=
tp://tex.stackexchange.com/q/120258/2966</a>). My initial thought (somewhat=
 bizarre, I=E2=80=99ll admit) was to save the option is a quark, set equal =
to one of a group of quarks.</div>
<div><br></div><div>Enrico pointed me in the direction of string comparison=
s, and I=E2=80=99ve moved to using code like this:<br><br>=C2=A0 =C2=A0 \ke=
ys_define:nn { jcsfonts }<br>=C2=A0 =C2=A0 =C2=A0 { font .choice_code:n =3D=
 \tl_gset:NV \g_jcsfonts_option_tl \l_keys_choice_tl }<br>
<br>=C2=A0 =C2=A0 \str_case:Vnn \g_jcsfonts_option_tl</div><div>=C2=A0 =C2=
=A0 =C2=A0 { { cmodern } {} % Computer Modern is LaTeX default</div><div>=
=C2=A0 =C2=A0 =C2=A0 =C2=A0 { kpfonts } { \RequirePackage{kpfonts} }</div><=
div>=C2=A0 =C2=A0 =C2=A0 } { \msg_error=E2=80=A6 }<br><br></div><div>
This works, but does not feel entirely satisfactory. Given my C background,=
 I=E2=80=99m tempted to write an enum package, loosely wrapping l3int, to b=
e used something like this:</div><div><br></div><div>=C2=A0 =C2=A0 \enum_ca=
se:Vnn \g_jcsfonts_option_enum</div>
<div>=C2=A0 =C2=A0 =C2=A0 { \c_jcsfonts_cmodern_enum=C2=A0{}</div><div>=C2=
=A0 =C2=A0 =C2=A0 =C2=A0 \c_jcsfonts_kpfonts_enum=C2=A0{ \RequirePackage{kp=
fonts} }</div><div>=C2=A0 =C2=A0 =C2=A0 } { \msg_error=E2=80=A6 }</div><div=
><br></div><div>It=E2=80=99s too early for anything to be idiomatic LaTeX3,=
 but what should *become* idiomatic?</div>
<div><br></div><div>=E2=80=94Joel</div></div>

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