From d751f070113da57a9193c0d189ede00811abc7d7 Mon Sep 17 00:00:00 2001
From: Martin Mares <mj@ucw.cz>
Date: Thu, 31 May 2018 16:28:46 +0200
Subject: [PATCH] Added facilities for defining macros with optional arguments

---
 ucwmac.tex | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/ucwmac.tex b/ucwmac.tex
index 9c99369..f49d765 100644
--- a/ucwmac.tex
+++ b/ucwmac.tex
@@ -94,6 +94,31 @@
 \setmargins{1truein}
 \setpaper{a4}
 
+%%% Macros with optional arguments %%%
+
+% After \def\a{\withoptarg\b}, the macro \a behaves in this way:
+%	\a[arg]		does \def\optarg{arg} and then it expands \b
+%	\a		does \let\optarg=\relax and then it expands \b
+\def\withoptarg#1{\let\xoptcall=#1\futurelet\next\xopt}
+\def\xopt{\ifx\next[\expandafter\xoptwith\else\let\optarg=\relax\expandafter\xoptcall\fi}
+\def\xoptwith[#1]{\def\optarg{#1}\xoptcall}
+
+% A shortcut for defining macros with optional arguments:
+% \optdef\macro behaves as \def\domacro, while \macro itself is defined
+% as a wrapper calling \domacro using \withoptarg.
+\def\optdef#1{%
+	\edef\xoptname{\expandafter\eatbackslash\string#1}%
+	\edef#1{\noexpand\withoptarg\csname do\xoptname\endcsname}%
+	\expandafter\def\csname do\xoptname\endcsname
+}
+
+% Trick: \eatbackslash eats the next backslash of category 12
+\begingroup\lccode`\+=`\\
+\lowercase{\endgroup\def\eatbackslash+{}}
+
+% Expand to the optional argument if it exists
+\def\optargorempty{\ifx\optarg\relax\else\optarg\fi}
+
 %%% Placing material at specified coordinates %%%
 
 % Set all dimensions of a given box register to zero
-- 
2.39.2