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LaTeX Cheatsheet: xparse

Syntax

xparse-declare ::= cmd-declare <cmd name> arg-spec <definition code>
                 | env-declare <env name> arg-spec <begin code> <end code>

cmd-declare    ::= "\\" prefix ["Expandable"] "DocumentCommand"
env-declare    ::= "\\" prefix "DocumentEnvironment"
prefix         ::= "New" | "Renew" | "Provide" | "Declare"

arg-spec       ::= argument*
argument       ::= processor* [modifier] arg-type

Note: notation introduced by Python Language Reference is used.

Example

\ExplSyntaxOn
\NewDocumentCommand \myCmd { s O{default} m }
  {
    \IfBooleanTF {#1} {star} {no-star},
    #1, #2
  }

\NewDocumentEnvironment {myEnv} { +m }
  {begin code} {end code}
\ExpleSyntaxOff

\myCmd{arg2}        % -> "no-star,default,arg2"
\myCmd*{arg2}       % -> "star,default,arg2"
\myCmd[arg1]{arg2}  % -> "no-star,arg1,arg2"

\begin{myEnv}{...}
\end{myEnv}

<prefix>: Name Prefix

Prefix If <cmd-name>/<env-name> defined If not defined
"New" ERROR run
"Renew" run ERROR
"Provide" ignored run
"Declare" run run

<arg-type>: Argument Type

Denoting Mandatory Argument

Type Meaning
m standard
r<char1><char2> delimited by <char1> and <char2>
R<char1><char2>{default} variant of r
v delimited like \verb
b denote the body of environment

Denoting Optional Argument

Type Meaning Tester
o standard \If(No)ValueTF
O{default} variant of o
d<char1><char2> delimited by <char1> and <char2> \If(No)ValueTF
D<char1><char2>{default} variant of d
s optional star * argument \IfBooleanTF
t<char> optional <char> argument \IfBooleanTF

<modifier>: Argument Modifier

Modifiers Meaning Examples
+ mark next argument as long +m
! ignore space-prefixed optional argument !o

<processor>: Argument Processor

processor ::= ">{" processor-function "}"
Processor function Meaning
\ReverseBoolean reverse logic of specifiers s or t
\SplitArgument{<number>}{<token(s)>} split argument into <number> + 1 parts by <tokens(s)>
\SplitList{<token(s)>} split argument into variable parts by <tokens(s)>
\TrimSpaces
user defined \procFunc<n args> - \procFunc accepts n + 1 argument(s)
- return processed argument as variable \ProcessedArgument

Examples

% \SplitArgument: split argument into fixed parts
> { \SplitArgument { 2 } { ; } } m

{a;b}     => {a}{b}{-NoValue-}
{a;b;c}   => {a}{b}{c}
{a;b;c;d} => ERROR (too many `;`s are present)

% \SplitList: split argument into variable parts
> { \SplitList { ; } } m

{a;b}     => {a}{b}
{a;b;c}   => {a}{b}{c}
{a;b;c;d} => {a}{b}{c}{d}

% \ProcessList: list-processing helper function
> { \foo } m

\NewDocumentCommand \foo { > { \SplitList { ; } } m }
  { \ProcessList {#1} { \map } }
\NewDocumentCommand \map { m }
  { |#1| }

{a;b}     => {|a|}{|b|}
{a;b;c}   => {|a|}{|b|}{|c|}
{a;b;c;d} => {|a|}{|b|}{|c|}{|d|}

Not Included

Argument types

  • denoting optional argument: e/E
  • backwards compatibility: mandatory l and u, optional g/G

See documentation of xparse package for full introduction.