How do I create a specially delimited command in `xparse`

Using def I can define a command as follows:

def

defaecmd#1 located at (#2);---definition---


I can recreate this with xparse as follows:

xparse

NewDocumentCommandaecmd u~located~at~(u);----definition---


However, I have a situation where I want to be able to write a command with an (almost final) optional argument. This would be a pain in the neck to do with def.

def

I'd like a command which could be expressed as either

aecmdManditory content[optional content] located at (location);


or

aecmdManditory content located at (location);


Essentially, I would like something that works like r but instead of taking a single token as the delimiters can take whole strings. Let's call this hypothetical argument specifier b

r

b

Then my desired command could be defined along these lines:

NewDocumentCommand{ mob~located~at~(); ---something---


I'm aware I could write something like that following:

NewDocumentCommandaecmd{ mou~located~at~(u);---definition---


Further, I suppose that I could test whether or not something was passed in the 3rd argument and raise an error if there was anything there.

But this just seems clunky. It doesn't feel right to me.

Any suggestions about how to do this better?

2 Answers
2

xparse? Pshaw!

xparse

EDITED to capture syntax error if optional argument is unbracketed.

documentclassarticle
usepackageparskip

newcommandaecmd[1]defmandatory#1aecmdaux
defaecmdaux#1 located at (#2);deflocation#2aecmdauxA#1
newcommandaecmdauxA[1]setbox0=hbox%
if[#1[gdefnextaecmdauxB#1else gdefnextsyntax errorfi%
next%

newcommandaecmdauxB[1]%
Optional: #1\ Mandatory: mandatory\ location: location

begindocument
aecmdColonel Mustard located at (the library);

aecmdColonel Mustard[with a wrench] located at (the library);

aecmdColonel Mustard on 4th street located at (the library);
enddocument


If one does not like the output of "syntax error" then in the definition of aecmdauxA, the words "syntax error" can be replaced with aecmdauxB and the effect will be to ignore the stray words in the syntax, while still producing the mandatory and location arguments.

aecmdauxA

aecmdauxB

aecmdColonel Mustard on 4th street located at (the library);

With xparse, but I find such syntax a very bad idea, notwithstanding TikZ using it.

xparse

documentclassarticle
usepackagexparse

ExplSyntaxOn
NewDocumentCommandaecmdmoulocated~at~(u);

tl_if_blank:nF #3 ERROR
noindent
#1~(mandatory)\
IfValueT#2#2~(optional)\
#4~(final)

ExplSyntaxOff

begindocument

aecmdMandatory content[optional content] located at (location);

aecmdMandatory content located at (location);

aecmdColonel Mustard on 4th street located at (the library);

enddocument


Note that the third call raises an error.

TikZ

xparse

Required, but never shown

Required, but never shown

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.