Expandable macro with loops and advanced string functions?
This is easy enough using expl3
(there are several possible approaches):
\documentclass{article}
\usepackage{expl3,xparse}
\ExplSyntaxOn
\DeclareExpandableDocumentCommand \mycmd { m }
{
\__mycmd_loop:nN {#1} aeiouAEIOU \q_recursion_tail \q_recursion_stop
}
\cs_new:Npn \__mycmd_loop:nN #1#2
{
\quark_if_recursion_tail_stop_do:nn {#2} { a }
\tl_if_head_eq_charcode:nNT {#1} #2
{
\use_i_delimit_by_q_recursion_stop:nw { an }
}
\__mycmd_loop:nN {#1}
}
\ExplSyntaxOff
\usepackage{mfirstuc}
\begin{document}
\mycmd{somestring} % should print "a "
\emakefirstuc{\mycmd{sometext}} % should print "A "
\mycmd{otherstring} % should print "an "
\emakefirstuc{\mycmd{otherstring}} % should print "An "
\end{document}
As \makefirstuc
does no expansion, I've had to use the e
version. I'd probably prefer to get around that by using the expandable (and Unicode-aware) \text_titlecase:n
:
\documentclass{article}
\usepackage{expl3,xparse}
\ExplSyntaxOn
\DeclareExpandableDocumentCommand \mycmd { m }
{
\__mycmd_loop:nN {#1} aeiouAEIOU \q_recursion_tail \q_recursion_stop
}
\cs_new:Npn \__mycmd_loop:nN #1#2
{
\quark_if_recursion_tail_stop_do:nn {#2} { a }
\tl_if_head_eq_charcode:nNT {#1} #2
{
\use_i_delimit_by_q_recursion_stop:nw { an }
}
\__mycmd_loop:nN {#1}
}
\cs_new_eq:NN \Mymakefirstuc \text_uppercase:n
\ExplSyntaxOff
\begin{document}
\mycmd{somestring} % should print "a "
\Mymakefirstuc{\mycmd{sometext}} % should print "A "
\mycmd{otherstring} % should print "an "
\Mymakefirstuc{\mycmd{otherstring}} % should print "An "
\end{document}
Depending on the number of cases, it might be desirable to lowercase all of the input first
\DeclareExpandableDocumentCommand \mycmd { m }
{
\exp_args:Nf \__mycmd:n { \text_lowercase:n {#1} }
}
\cs_new:Npn \__mycmd:n #1
{
\__mycmd_loop:nN {#1} aeiou \q_recursion_tail \q_recursion_stop
}
Here's an approach with expl3
\documentclass{article}
\usepackage{xparse,glossaries}
\ExplSyntaxOn
\DeclareExpandableDocumentCommand{\indef}{m}
{
\str_case_x:nnF { \tl_head:f { \tl_lower_case:n { #1 } } }
{
{a}{an}
{e}{an}
{i}{an}
{o}{an}
{u}{an}
}
{a}~#1
}
\ExplSyntaxOff
\begin{document}
\indef{abc} --- \indef{cde} --- \indef{ABC} --- \indef{CDE}
\emakefirstuc{\indef{abc}} --- \emakefirstuc{\indef{cde}} ---
\emakefirstuc{\indef{ABC}} --- \emakefirstuc{\indef{CDE}}
\end{document}
Here's a LuaLaTeX-based solution. It defines two fully-expandable "wrapper" macros named \mycmd
and \mkfirstuc
, which pass their arguments to Lua functions named mycmd
and mkfirstuc
. The Lua functions perform the actual work of prefixing "an " or "a " to a string and of upper-casing the first character in the string, respectively.
% !TEX TS-program = lualatex
\documentclass{article}
%% Lua-side code
\usepackage{luacode}
\begin{luacode}
function mycmd ( s )
if string.match ( string.sub(s,1,1) , "[aeiouAEIOU]" ) then
return tex.sprint ("an " .. s)
else
return tex.sprint ("a " .. s)
end
end
function mkfirstuc ( s )
return tex.sprint ( string.upper(string.sub(s,1,1)) .. string.sub(s,2) )
end
\end{luacode}
%% TeX-side code
\newcommand\mycmd[1]{\directlua{mycmd(\luastring{#1})}}
\newcommand\mkfirstuc[1]{\directlua{mkfirstuc(\luastring{#1})}}
\begin{document}
\mycmd{abc}, \mycmd{def}, \mycmd{ABC}, \mycmd{DEF}.
\mkfirstuc{\mycmd{abc}}, \mkfirstuc{\mycmd{def}},
\mkfirstuc{\mycmd{ABC}}, \mkfirstuc{\mycmd{DEF}}.
\end{document}