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Date:         Mon, 14 Apr 2014 15:30:29 +0200
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From: =?ISO-8859-1?Q?Lars_Hellstr=F6m?= <Lars.Hellstrom@RESIDENSET.NET>
Subject: Variable functions, or function-valued variables
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Status: R

I just noticed another point where the expl3 naming rules doesn't say wha=
t=20
to do: what if I have a variable that is also a function? In traditional=20
imperative languages those may seem like exclusive categories, but in=20
(La)TeX programming it is sometimes perfectly natural, and quite=20
straightforward.

The typical example of this would be a callback function: something that =
a=20
module calls at specified points, but which the user of that module is=20
expected to define. Treating this as just a function loses the specificat=
ion=20
of the scope for that variable. Treating it as a variable of type tl lose=
s=20
the specification that it takes arguments. What I found natural is to use=
 a=20
name of the form

   \<SCOPE>_<MODULE>_<DESCRIPTION>:<ARG-SPEC>

e.g.

   \l_harmless_callback:nn

This could be interpreted both as adding a SCOPE part to function names (=
the=20
vast majority of functions without a SCOPE are implicity considered to be=
 c_=20
constant), or alternatively as proclaiming any :<ARG-SPEC> to be a valid=20
_<TYPE> for a variable.

Lars Hellstr=F6m