How to define a command with two optional arguments?

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up vote
7
down vote

favorite

2

I would like to have a single command that can take either 1, 2, or 3 arguments and do something different for each number of arguments.

ca -> C_a
cab -> C_a^[b]
cabc -> C_a,c^[b]

Since Latex has no command overloading, I decided that optional arguments are good enough:

ca -> C_a
c[b]a -> C_a^[b]
c[c][b]a -> C_a,c^[b]

I found that this great answer using xparse might do exactly what I need. However his answer works only for 2 optional arguments. He mentions how to extend it to any number of arguments, but I couldn't figure it out. I tried:

usepackagexparse
....
DeclareDocumentCommand c o o m %
 IfNoValueTF #1 %
 IfNoValueTF #2 %
 C_#3%
 %
 C_#3^[#2]%
 %
 %
 C_#2, #3^[#1]%
 % 


$ca c[b]a c[c][b]a$ 

But it seems that I cannot get the branch with two arguments to work:

What am I doing wrong?

macros xparse optional-arguments

share|improve this question

asked Aug 30 at 17:34

Martin Drozdik

82931527

• 
  
  
  

  
  

  
  
  
  
  
  

  
  In LaTeX you don't need braces with undelimited single-token-arguments. Thus: How to handle cabc? Shall this mean c has one arg and the one-arg-call to c is trailed by letters b and c which do not form args of c? Shall this mean a three-argument-call to c with two args just not being nested in braces as braces are not really needed with single-token-arguments? You can check if a single-argument-macro's arg in turn consists of three or two or one brace-delimited arguments, i.e., cabc, but then you need to specify behavior for other cases and spaces as well.
  – Ulrich Diez
  Aug 31 at 16:56
  
  

  
  
  
  

add a comment | 

up vote
7
down vote

favorite

2

I would like to have a single command that can take either 1, 2, or 3 arguments and do something different for each number of arguments.

ca -> C_a
cab -> C_a^[b]
cabc -> C_a,c^[b]

Since Latex has no command overloading, I decided that optional arguments are good enough:

ca -> C_a
c[b]a -> C_a^[b]
c[c][b]a -> C_a,c^[b]

I found that this great answer using xparse might do exactly what I need. However his answer works only for 2 optional arguments. He mentions how to extend it to any number of arguments, but I couldn't figure it out. I tried:

usepackagexparse
....
DeclareDocumentCommand c o o m %
 IfNoValueTF #1 %
 IfNoValueTF #2 %
 C_#3%
 %
 C_#3^[#2]%
 %
 %
 C_#2, #3^[#1]%
 % 


$ca c[b]a c[c][b]a$ 

But it seems that I cannot get the branch with two arguments to work:

What am I doing wrong?

macros xparse optional-arguments

share|improve this question

asked Aug 30 at 17:34

Martin Drozdik

82931527

• 
  
  
  

  
  

  
  
  
  
  
  

  
  In LaTeX you don't need braces with undelimited single-token-arguments. Thus: How to handle cabc? Shall this mean c has one arg and the one-arg-call to c is trailed by letters b and c which do not form args of c? Shall this mean a three-argument-call to c with two args just not being nested in braces as braces are not really needed with single-token-arguments? You can check if a single-argument-macro's arg in turn consists of three or two or one brace-delimited arguments, i.e., cabc, but then you need to specify behavior for other cases and spaces as well.
  – Ulrich Diez
  Aug 31 at 16:56
  
  

  
  
  
  

add a comment | 

up vote
7
down vote

favorite

2

up vote
7
down vote

favorite

2

2

I would like to have a single command that can take either 1, 2, or 3 arguments and do something different for each number of arguments.

ca -> C_a
cab -> C_a^[b]
cabc -> C_a,c^[b]

Since Latex has no command overloading, I decided that optional arguments are good enough:

ca -> C_a
c[b]a -> C_a^[b]
c[c][b]a -> C_a,c^[b]

I found that this great answer using xparse might do exactly what I need. However his answer works only for 2 optional arguments. He mentions how to extend it to any number of arguments, but I couldn't figure it out. I tried:

usepackagexparse
....
DeclareDocumentCommand c o o m %
 IfNoValueTF #1 %
 IfNoValueTF #2 %
 C_#3%
 %
 C_#3^[#2]%
 %
 %
 C_#2, #3^[#1]%
 % 


$ca c[b]a c[c][b]a$ 

But it seems that I cannot get the branch with two arguments to work:

What am I doing wrong?

macros xparse optional-arguments

share|improve this question

asked Aug 30 at 17:34

Martin Drozdik

82931527

I would like to have a single command that can take either 1, 2, or 3 arguments and do something different for each number of arguments.

ca -> C_a
cab -> C_a^[b]
cabc -> C_a,c^[b]

Since Latex has no command overloading, I decided that optional arguments are good enough:

ca -> C_a
c[b]a -> C_a^[b]
c[c][b]a -> C_a,c^[b]

I found that this great answer using xparse might do exactly what I need. However his answer works only for 2 optional arguments. He mentions how to extend it to any number of arguments, but I couldn't figure it out. I tried:

usepackagexparse
....
DeclareDocumentCommand c o o m %
 IfNoValueTF #1 %
 IfNoValueTF #2 %
 C_#3%
 %
 C_#3^[#2]%
 %
 %
 C_#2, #3^[#1]%
 % 


$ca c[b]a c[c][b]a$ 

But it seems that I cannot get the branch with two arguments to work:

What am I doing wrong?

macros xparse optional-arguments

share|improve this question

asked Aug 30 at 17:34

Martin Drozdik

82931527

share|improve this question

share|improve this question

asked Aug 30 at 17:34

Martin Drozdik

82931527

asked Aug 30 at 17:34

Martin Drozdik

82931527

asked Aug 30 at 17:34

Martin Drozdik

82931527

82931527

• 
  
  
  

  
  

  
  
  
  
  
  

  
  In LaTeX you don't need braces with undelimited single-token-arguments. Thus: How to handle cabc? Shall this mean c has one arg and the one-arg-call to c is trailed by letters b and c which do not form args of c? Shall this mean a three-argument-call to c with two args just not being nested in braces as braces are not really needed with single-token-arguments? You can check if a single-argument-macro's arg in turn consists of three or two or one brace-delimited arguments, i.e., cabc, but then you need to specify behavior for other cases and spaces as well.
  – Ulrich Diez
  Aug 31 at 16:56
  
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  In LaTeX you don't need braces with undelimited single-token-arguments. Thus: How to handle cabc? Shall this mean c has one arg and the one-arg-call to c is trailed by letters b and c which do not form args of c? Shall this mean a three-argument-call to c with two args just not being nested in braces as braces are not really needed with single-token-arguments? You can check if a single-argument-macro's arg in turn consists of three or two or one brace-delimited arguments, i.e., cabc, but then you need to specify behavior for other cases and spaces as well.
  – Ulrich Diez
  Aug 31 at 16:56
  
  

  
  
  
  

In LaTeX you don't need braces with undelimited single-token-arguments. Thus: How to handle cabc? Shall this mean c has one arg and the one-arg-call to c is trailed by letters b and c which do not form args of c? Shall this mean a three-argument-call to c with two args just not being nested in braces as braces are not really needed with single-token-arguments? You can check if a single-argument-macro's arg in turn consists of three or two or one brace-delimited arguments, i.e., cabc, but then you need to specify behavior for other cases and spaces as well.
– Ulrich Diez
Aug 31 at 16:56

In LaTeX you don't need braces with undelimited single-token-arguments. Thus: How to handle cabc? Shall this mean c has one arg and the one-arg-call to c is trailed by letters b and c which do not form args of c? Shall this mean a three-argument-call to c with two args just not being nested in braces as braces are not really needed with single-token-arguments? You can check if a single-argument-macro's arg in turn consists of three or two or one brace-delimited arguments, i.e., cabc, but then you need to specify behavior for other cases and spaces as well.
– Ulrich Diez
Aug 31 at 16:56

add a comment | 

2 Answers
2

active

oldest

votes

up vote
7
down vote



accepted

You should start from examining #2 rather than #1, because #2 only can have a value if #1 has, too.

documentclassarticle
usepackagexparse

NewDocumentCommand C o o m %
 IfNoValueTF#2
 %
 IfNoValueTF #1
 %
 C_#3%
 
 %
 C_#3^[#1]%
 %
 
 %
 C_#3, #1^[#2]%
 % 


begindocument

$Ca quad C[b]a quad C[c][b]a$ 

enddocument

And don't use DeclareDocumentCommand to override the meaning of c: you'll regret it when you have to cite some French or Turkish author with “ç” in their name.

share|improve this answer

answered Aug 30 at 17:48

egreg

681k8318083056

add a comment | 

up vote
1
down vote

You wish to define a macro c. But c is already defined in LaTeX.

Therefore I will henceforth not refer to the macro in question as c.

Instead I will refer to the macro in question as macroc.

---

Are you aware that in TeX/LaTeX undelimited arguments consisting of a single token don't need to be nested in braces?

After defining newcommandfoo[1]This is argument 1: #1.,
foob will yield the same result as
foo b.

After defining newcommandbar[2]This is argument 1: #1. This is argument 2: #2., the following calls will all yield the same result:
barab
bar ab
bar ab
bar ab
bara b
bar a b
bar a b
bar a b

This is because

1. you don't need braces when undelimited arguments consist of a single token.


2. (La)TeX does discard space tokens preceding undelimited arguments.

When called as macrocabc—how shall macroc "know" whether the user intends to have c as macroc's third argument which consists of the single token c or whether the user intends to have macroc called with only two arguments, namely a and b while c shall not be considered a third argument?

The situation is ambiguous.

You can turn the situation into something unambiguous by having macroc process only one undelimited argument and having macroc check whether that argument in turn is of one of the patterns

⟨argument 1⟩

⟨argument 1⟩⟨argument 2⟩

⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

and having macroc act accordingly in case one of these patterns is detected and having macroc deliver an error-message otherwise.

I.e.,

macroc⟨argument 1⟩

macroc⟨argument 1⟩⟨argument 2⟩

macroc⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

---

With the example below, macroc does process one undelimited argument.

Syntax: macroc⟨argument⟩.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩,
macrocatonearg⟨argument 1⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩,
macrocattwoargs⟨argument 1⟩⟨argument 2⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩,
macrocatthreeargs⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩ will be carried out.

In all other cases an error-message will inform the user about a syntax-error.

Thus you can do, e.g., :

macroca

macrocab

macrocabc

documentclassarticle

makeatletter
%%=============================================================================
%% Paraphernalia:
%% UD@firstoftwo, UD@secondoftwo,
%% UD@gobble, UD@gobbletwo, UD@gobblethree
%% UD@CheckWhetherNull, UD@CheckWhetherBrace,
%%=============================================================================
newcommandUD@firstoftwo[2]#1%
newcommandUD@secondoftwo[2]#2%
newcommandUD@gobble[1]%
newcommandUD@gobbletwo[2]%
newcommandUD@gobblethree[3]%
%%-----------------------------------------------------------------------------
%% Check whether argument is empty:
%%.............................................................................
%% UD@CheckWhetherNull<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is empty>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is not empty>%
%%
%% The gist of this macro comes from Robert R. Schneck's ifempty-macro:
%% <https://groups.google.com/forum/#!original/comp.text.tex/kuOEIQIrElc/lUg37FmhA74J>
newcommandUD@CheckWhetherNull[1]%
 romannumeral0expandafterUD@secondoftwostringexpandafter
 UD@secondoftwoexpandafterexpandafterstring#1expandafter
 UD@secondoftwostringexpandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@secondoftwoexpandafterexpandafterUD@firstoftwo UD@firstoftwo%
%
%%-----------------------------------------------------------------------------
%% Check whether argument's first token is a catcode-1-character
%%.............................................................................
%% UD@CheckWhetherBrace<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has leading
%% catcode-1-token>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has no leading
%% catcode-1-token>%
newcommandUD@CheckWhetherBrace[1]%
 romannumeral0expandafterUD@secondoftwoexpandafterexpandafter%
 string#1.expandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@firstoftwoexpandafterexpandafterUD@firstoftwo UD@secondoftwo%
%
%%=============================================================================
%% macroc for processing one argument within which
%% you may have one or two or three brace-nested arguments:
%%-----------------------------------------------------------------------------
newcommandmacrocatonearg[1]C_#1%
newcommandmacrocattwoargs[2]C_#1^[#2]%
newcommandmacrocatthreeargs[3]C_#1,#3^[#2]%
newcommandmacrocatsyntaxerror%
 @latex@errorIncorrect SyntaxSpecify either one or two or three arguments that are nested in braces.%
%
newcommandmacroc[1]%
 UD@CheckWhetherBrace#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobble#1%
 macrocatonearg#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobble#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobbletwo#1%
 macrocattwoargs#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobbletwo#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobblethree#1%
 macrocatthreeargs#1%
 macrocatsyntaxerror%
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
%
makeatother
begindocument

verb|$macroca$|: $macroca$ bigskip

verb|$macrocab$|: $macrocab$ bigskip

verb|$macrocabc$|: $macrocabc$ bigskip

% Syntax-errors:
% 
% $macrocabcd$
%
% $macroc a$
% 
% $macroca b$
%
% $macroca$
%
% $macroc$

enddocument

share|improve this answer

edited Sep 3 at 16:02

answered Aug 31 at 17:42

Ulrich Diez

3,250414

add a comment | 

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

active

oldest

votes

active

oldest

votes

up vote
7
down vote



accepted

You should start from examining #2 rather than #1, because #2 only can have a value if #1 has, too.

documentclassarticle
usepackagexparse

NewDocumentCommand C o o m %
 IfNoValueTF#2
 %
 IfNoValueTF #1
 %
 C_#3%
 
 %
 C_#3^[#1]%
 %
 
 %
 C_#3, #1^[#2]%
 % 


begindocument

$Ca quad C[b]a quad C[c][b]a$ 

enddocument

And don't use DeclareDocumentCommand to override the meaning of c: you'll regret it when you have to cite some French or Turkish author with “ç” in their name.

share|improve this answer

answered Aug 30 at 17:48

egreg

681k8318083056

add a comment | 

up vote
7
down vote



accepted

You should start from examining #2 rather than #1, because #2 only can have a value if #1 has, too.

documentclassarticle
usepackagexparse

NewDocumentCommand C o o m %
 IfNoValueTF#2
 %
 IfNoValueTF #1
 %
 C_#3%
 
 %
 C_#3^[#1]%
 %
 
 %
 C_#3, #1^[#2]%
 % 


begindocument

$Ca quad C[b]a quad C[c][b]a$ 

enddocument

And don't use DeclareDocumentCommand to override the meaning of c: you'll regret it when you have to cite some French or Turkish author with “ç” in their name.

share|improve this answer

answered Aug 30 at 17:48

egreg

681k8318083056

add a comment | 

up vote
7
down vote



accepted

up vote
7
down vote



accepted

You should start from examining #2 rather than #1, because #2 only can have a value if #1 has, too.

documentclassarticle
usepackagexparse

NewDocumentCommand C o o m %
 IfNoValueTF#2
 %
 IfNoValueTF #1
 %
 C_#3%
 
 %
 C_#3^[#1]%
 %
 
 %
 C_#3, #1^[#2]%
 % 


begindocument

$Ca quad C[b]a quad C[c][b]a$ 

enddocument

And don't use DeclareDocumentCommand to override the meaning of c: you'll regret it when you have to cite some French or Turkish author with “ç” in their name.

share|improve this answer

answered Aug 30 at 17:48

egreg

681k8318083056

You should start from examining #2 rather than #1, because #2 only can have a value if #1 has, too.

documentclassarticle
usepackagexparse

NewDocumentCommand C o o m %
 IfNoValueTF#2
 %
 IfNoValueTF #1
 %
 C_#3%
 
 %
 C_#3^[#1]%
 %
 
 %
 C_#3, #1^[#2]%
 % 


begindocument

$Ca quad C[b]a quad C[c][b]a$ 

enddocument

And don't use DeclareDocumentCommand to override the meaning of c: you'll regret it when you have to cite some French or Turkish author with “ç” in their name.

share|improve this answer

answered Aug 30 at 17:48

egreg

681k8318083056

share|improve this answer

share|improve this answer

answered Aug 30 at 17:48

egreg

681k8318083056

answered Aug 30 at 17:48

egreg

681k8318083056

answered Aug 30 at 17:48

egreg

681k8318083056

681k8318083056

add a comment | 

add a comment | 

up vote
1
down vote

You wish to define a macro c. But c is already defined in LaTeX.

Therefore I will henceforth not refer to the macro in question as c.

Instead I will refer to the macro in question as macroc.

---

Are you aware that in TeX/LaTeX undelimited arguments consisting of a single token don't need to be nested in braces?

After defining newcommandfoo[1]This is argument 1: #1.,
foob will yield the same result as
foo b.

After defining newcommandbar[2]This is argument 1: #1. This is argument 2: #2., the following calls will all yield the same result:
barab
bar ab
bar ab
bar ab
bara b
bar a b
bar a b
bar a b

This is because

1. you don't need braces when undelimited arguments consist of a single token.


2. (La)TeX does discard space tokens preceding undelimited arguments.

When called as macrocabc—how shall macroc "know" whether the user intends to have c as macroc's third argument which consists of the single token c or whether the user intends to have macroc called with only two arguments, namely a and b while c shall not be considered a third argument?

The situation is ambiguous.

You can turn the situation into something unambiguous by having macroc process only one undelimited argument and having macroc check whether that argument in turn is of one of the patterns

⟨argument 1⟩

⟨argument 1⟩⟨argument 2⟩

⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

and having macroc act accordingly in case one of these patterns is detected and having macroc deliver an error-message otherwise.

I.e.,

macroc⟨argument 1⟩

macroc⟨argument 1⟩⟨argument 2⟩

macroc⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

---

With the example below, macroc does process one undelimited argument.

Syntax: macroc⟨argument⟩.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩,
macrocatonearg⟨argument 1⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩,
macrocattwoargs⟨argument 1⟩⟨argument 2⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩,
macrocatthreeargs⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩ will be carried out.

In all other cases an error-message will inform the user about a syntax-error.

Thus you can do, e.g., :

macroca

macrocab

macrocabc

documentclassarticle

makeatletter
%%=============================================================================
%% Paraphernalia:
%% UD@firstoftwo, UD@secondoftwo,
%% UD@gobble, UD@gobbletwo, UD@gobblethree
%% UD@CheckWhetherNull, UD@CheckWhetherBrace,
%%=============================================================================
newcommandUD@firstoftwo[2]#1%
newcommandUD@secondoftwo[2]#2%
newcommandUD@gobble[1]%
newcommandUD@gobbletwo[2]%
newcommandUD@gobblethree[3]%
%%-----------------------------------------------------------------------------
%% Check whether argument is empty:
%%.............................................................................
%% UD@CheckWhetherNull<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is empty>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is not empty>%
%%
%% The gist of this macro comes from Robert R. Schneck's ifempty-macro:
%% <https://groups.google.com/forum/#!original/comp.text.tex/kuOEIQIrElc/lUg37FmhA74J>
newcommandUD@CheckWhetherNull[1]%
 romannumeral0expandafterUD@secondoftwostringexpandafter
 UD@secondoftwoexpandafterexpandafterstring#1expandafter
 UD@secondoftwostringexpandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@secondoftwoexpandafterexpandafterUD@firstoftwo UD@firstoftwo%
%
%%-----------------------------------------------------------------------------
%% Check whether argument's first token is a catcode-1-character
%%.............................................................................
%% UD@CheckWhetherBrace<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has leading
%% catcode-1-token>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has no leading
%% catcode-1-token>%
newcommandUD@CheckWhetherBrace[1]%
 romannumeral0expandafterUD@secondoftwoexpandafterexpandafter%
 string#1.expandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@firstoftwoexpandafterexpandafterUD@firstoftwo UD@secondoftwo%
%
%%=============================================================================
%% macroc for processing one argument within which
%% you may have one or two or three brace-nested arguments:
%%-----------------------------------------------------------------------------
newcommandmacrocatonearg[1]C_#1%
newcommandmacrocattwoargs[2]C_#1^[#2]%
newcommandmacrocatthreeargs[3]C_#1,#3^[#2]%
newcommandmacrocatsyntaxerror%
 @latex@errorIncorrect SyntaxSpecify either one or two or three arguments that are nested in braces.%
%
newcommandmacroc[1]%
 UD@CheckWhetherBrace#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobble#1%
 macrocatonearg#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobble#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobbletwo#1%
 macrocattwoargs#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobbletwo#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobblethree#1%
 macrocatthreeargs#1%
 macrocatsyntaxerror%
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
%
makeatother
begindocument

verb|$macroca$|: $macroca$ bigskip

verb|$macrocab$|: $macrocab$ bigskip

verb|$macrocabc$|: $macrocabc$ bigskip

% Syntax-errors:
% 
% $macrocabcd$
%
% $macroc a$
% 
% $macroca b$
%
% $macroca$
%
% $macroc$

enddocument

share|improve this answer

edited Sep 3 at 16:02

answered Aug 31 at 17:42

Ulrich Diez

3,250414

add a comment | 

up vote
1
down vote

You wish to define a macro c. But c is already defined in LaTeX.

Therefore I will henceforth not refer to the macro in question as c.

Instead I will refer to the macro in question as macroc.

---

Are you aware that in TeX/LaTeX undelimited arguments consisting of a single token don't need to be nested in braces?

After defining newcommandfoo[1]This is argument 1: #1.,
foob will yield the same result as
foo b.

After defining newcommandbar[2]This is argument 1: #1. This is argument 2: #2., the following calls will all yield the same result:
barab
bar ab
bar ab
bar ab
bara b
bar a b
bar a b
bar a b

This is because

1. you don't need braces when undelimited arguments consist of a single token.


2. (La)TeX does discard space tokens preceding undelimited arguments.

When called as macrocabc—how shall macroc "know" whether the user intends to have c as macroc's third argument which consists of the single token c or whether the user intends to have macroc called with only two arguments, namely a and b while c shall not be considered a third argument?

The situation is ambiguous.

You can turn the situation into something unambiguous by having macroc process only one undelimited argument and having macroc check whether that argument in turn is of one of the patterns

⟨argument 1⟩

⟨argument 1⟩⟨argument 2⟩

⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

and having macroc act accordingly in case one of these patterns is detected and having macroc deliver an error-message otherwise.

I.e.,

macroc⟨argument 1⟩

macroc⟨argument 1⟩⟨argument 2⟩

macroc⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

---

With the example below, macroc does process one undelimited argument.

Syntax: macroc⟨argument⟩.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩,
macrocatonearg⟨argument 1⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩,
macrocattwoargs⟨argument 1⟩⟨argument 2⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩,
macrocatthreeargs⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩ will be carried out.

In all other cases an error-message will inform the user about a syntax-error.

Thus you can do, e.g., :

macroca

macrocab

macrocabc

documentclassarticle

makeatletter
%%=============================================================================
%% Paraphernalia:
%% UD@firstoftwo, UD@secondoftwo,
%% UD@gobble, UD@gobbletwo, UD@gobblethree
%% UD@CheckWhetherNull, UD@CheckWhetherBrace,
%%=============================================================================
newcommandUD@firstoftwo[2]#1%
newcommandUD@secondoftwo[2]#2%
newcommandUD@gobble[1]%
newcommandUD@gobbletwo[2]%
newcommandUD@gobblethree[3]%
%%-----------------------------------------------------------------------------
%% Check whether argument is empty:
%%.............................................................................
%% UD@CheckWhetherNull<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is empty>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is not empty>%
%%
%% The gist of this macro comes from Robert R. Schneck's ifempty-macro:
%% <https://groups.google.com/forum/#!original/comp.text.tex/kuOEIQIrElc/lUg37FmhA74J>
newcommandUD@CheckWhetherNull[1]%
 romannumeral0expandafterUD@secondoftwostringexpandafter
 UD@secondoftwoexpandafterexpandafterstring#1expandafter
 UD@secondoftwostringexpandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@secondoftwoexpandafterexpandafterUD@firstoftwo UD@firstoftwo%
%
%%-----------------------------------------------------------------------------
%% Check whether argument's first token is a catcode-1-character
%%.............................................................................
%% UD@CheckWhetherBrace<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has leading
%% catcode-1-token>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has no leading
%% catcode-1-token>%
newcommandUD@CheckWhetherBrace[1]%
 romannumeral0expandafterUD@secondoftwoexpandafterexpandafter%
 string#1.expandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@firstoftwoexpandafterexpandafterUD@firstoftwo UD@secondoftwo%
%
%%=============================================================================
%% macroc for processing one argument within which
%% you may have one or two or three brace-nested arguments:
%%-----------------------------------------------------------------------------
newcommandmacrocatonearg[1]C_#1%
newcommandmacrocattwoargs[2]C_#1^[#2]%
newcommandmacrocatthreeargs[3]C_#1,#3^[#2]%
newcommandmacrocatsyntaxerror%
 @latex@errorIncorrect SyntaxSpecify either one or two or three arguments that are nested in braces.%
%
newcommandmacroc[1]%
 UD@CheckWhetherBrace#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobble#1%
 macrocatonearg#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobble#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobbletwo#1%
 macrocattwoargs#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobbletwo#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobblethree#1%
 macrocatthreeargs#1%
 macrocatsyntaxerror%
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
%
makeatother
begindocument

verb|$macroca$|: $macroca$ bigskip

verb|$macrocab$|: $macrocab$ bigskip

verb|$macrocabc$|: $macrocabc$ bigskip

% Syntax-errors:
% 
% $macrocabcd$
%
% $macroc a$
% 
% $macroca b$
%
% $macroca$
%
% $macroc$

enddocument

share|improve this answer

edited Sep 3 at 16:02

answered Aug 31 at 17:42

Ulrich Diez

3,250414

add a comment | 

up vote
1
down vote

up vote
1
down vote

You wish to define a macro c. But c is already defined in LaTeX.

Therefore I will henceforth not refer to the macro in question as c.

Instead I will refer to the macro in question as macroc.

---

Are you aware that in TeX/LaTeX undelimited arguments consisting of a single token don't need to be nested in braces?

After defining newcommandfoo[1]This is argument 1: #1.,
foob will yield the same result as
foo b.

After defining newcommandbar[2]This is argument 1: #1. This is argument 2: #2., the following calls will all yield the same result:
barab
bar ab
bar ab
bar ab
bara b
bar a b
bar a b
bar a b

This is because

1. you don't need braces when undelimited arguments consist of a single token.


2. (La)TeX does discard space tokens preceding undelimited arguments.

When called as macrocabc—how shall macroc "know" whether the user intends to have c as macroc's third argument which consists of the single token c or whether the user intends to have macroc called with only two arguments, namely a and b while c shall not be considered a third argument?

The situation is ambiguous.

You can turn the situation into something unambiguous by having macroc process only one undelimited argument and having macroc check whether that argument in turn is of one of the patterns

⟨argument 1⟩

⟨argument 1⟩⟨argument 2⟩

⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

and having macroc act accordingly in case one of these patterns is detected and having macroc deliver an error-message otherwise.

I.e.,

macroc⟨argument 1⟩

macroc⟨argument 1⟩⟨argument 2⟩

macroc⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

---

With the example below, macroc does process one undelimited argument.

Syntax: macroc⟨argument⟩.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩,
macrocatonearg⟨argument 1⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩,
macrocattwoargs⟨argument 1⟩⟨argument 2⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩,
macrocatthreeargs⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩ will be carried out.

In all other cases an error-message will inform the user about a syntax-error.

Thus you can do, e.g., :

macroca

macrocab

macrocabc

documentclassarticle

makeatletter
%%=============================================================================
%% Paraphernalia:
%% UD@firstoftwo, UD@secondoftwo,
%% UD@gobble, UD@gobbletwo, UD@gobblethree
%% UD@CheckWhetherNull, UD@CheckWhetherBrace,
%%=============================================================================
newcommandUD@firstoftwo[2]#1%
newcommandUD@secondoftwo[2]#2%
newcommandUD@gobble[1]%
newcommandUD@gobbletwo[2]%
newcommandUD@gobblethree[3]%
%%-----------------------------------------------------------------------------
%% Check whether argument is empty:
%%.............................................................................
%% UD@CheckWhetherNull<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is empty>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is not empty>%
%%
%% The gist of this macro comes from Robert R. Schneck's ifempty-macro:
%% <https://groups.google.com/forum/#!original/comp.text.tex/kuOEIQIrElc/lUg37FmhA74J>
newcommandUD@CheckWhetherNull[1]%
 romannumeral0expandafterUD@secondoftwostringexpandafter
 UD@secondoftwoexpandafterexpandafterstring#1expandafter
 UD@secondoftwostringexpandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@secondoftwoexpandafterexpandafterUD@firstoftwo UD@firstoftwo%
%
%%-----------------------------------------------------------------------------
%% Check whether argument's first token is a catcode-1-character
%%.............................................................................
%% UD@CheckWhetherBrace<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has leading
%% catcode-1-token>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has no leading
%% catcode-1-token>%
newcommandUD@CheckWhetherBrace[1]%
 romannumeral0expandafterUD@secondoftwoexpandafterexpandafter%
 string#1.expandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@firstoftwoexpandafterexpandafterUD@firstoftwo UD@secondoftwo%
%
%%=============================================================================
%% macroc for processing one argument within which
%% you may have one or two or three brace-nested arguments:
%%-----------------------------------------------------------------------------
newcommandmacrocatonearg[1]C_#1%
newcommandmacrocattwoargs[2]C_#1^[#2]%
newcommandmacrocatthreeargs[3]C_#1,#3^[#2]%
newcommandmacrocatsyntaxerror%
 @latex@errorIncorrect SyntaxSpecify either one or two or three arguments that are nested in braces.%
%
newcommandmacroc[1]%
 UD@CheckWhetherBrace#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobble#1%
 macrocatonearg#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobble#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobbletwo#1%
 macrocattwoargs#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobbletwo#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobblethree#1%
 macrocatthreeargs#1%
 macrocatsyntaxerror%
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
%
makeatother
begindocument

verb|$macroca$|: $macroca$ bigskip

verb|$macrocab$|: $macrocab$ bigskip

verb|$macrocabc$|: $macrocabc$ bigskip

% Syntax-errors:
% 
% $macrocabcd$
%
% $macroc a$
% 
% $macroca b$
%
% $macroca$
%
% $macroc$

enddocument

share|improve this answer

edited Sep 3 at 16:02

answered Aug 31 at 17:42

Ulrich Diez

3,250414

You wish to define a macro c. But c is already defined in LaTeX.

Therefore I will henceforth not refer to the macro in question as c.

Instead I will refer to the macro in question as macroc.

---

Are you aware that in TeX/LaTeX undelimited arguments consisting of a single token don't need to be nested in braces?

After defining newcommandfoo[1]This is argument 1: #1.,
foob will yield the same result as
foo b.

After defining newcommandbar[2]This is argument 1: #1. This is argument 2: #2., the following calls will all yield the same result:
barab
bar ab
bar ab
bar ab
bara b
bar a b
bar a b
bar a b

This is because

1. you don't need braces when undelimited arguments consist of a single token.


2. (La)TeX does discard space tokens preceding undelimited arguments.

When called as macrocabc—how shall macroc "know" whether the user intends to have c as macroc's third argument which consists of the single token c or whether the user intends to have macroc called with only two arguments, namely a and b while c shall not be considered a third argument?

The situation is ambiguous.

You can turn the situation into something unambiguous by having macroc process only one undelimited argument and having macroc check whether that argument in turn is of one of the patterns

⟨argument 1⟩

⟨argument 1⟩⟨argument 2⟩

⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

and having macroc act accordingly in case one of these patterns is detected and having macroc deliver an error-message otherwise.

I.e.,

macroc⟨argument 1⟩

macroc⟨argument 1⟩⟨argument 2⟩

macroc⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩

---

With the example below, macroc does process one undelimited argument.

Syntax: macroc⟨argument⟩.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩,
macrocatonearg⟨argument 1⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩,
macrocattwoargs⟨argument 1⟩⟨argument 2⟩ will be carried out.

In case ⟨argument⟩ is of pattern ⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩,
macrocatthreeargs⟨argument 1⟩⟨argument 2⟩⟨argument 3⟩ will be carried out.

In all other cases an error-message will inform the user about a syntax-error.

Thus you can do, e.g., :

macroca

macrocab

macrocabc

documentclassarticle

makeatletter
%%=============================================================================
%% Paraphernalia:
%% UD@firstoftwo, UD@secondoftwo,
%% UD@gobble, UD@gobbletwo, UD@gobblethree
%% UD@CheckWhetherNull, UD@CheckWhetherBrace,
%%=============================================================================
newcommandUD@firstoftwo[2]#1%
newcommandUD@secondoftwo[2]#2%
newcommandUD@gobble[1]%
newcommandUD@gobbletwo[2]%
newcommandUD@gobblethree[3]%
%%-----------------------------------------------------------------------------
%% Check whether argument is empty:
%%.............................................................................
%% UD@CheckWhetherNull<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is empty>%
%% <Tokens to be delivered in case that argument
%% which is to be checked is not empty>%
%%
%% The gist of this macro comes from Robert R. Schneck's ifempty-macro:
%% <https://groups.google.com/forum/#!original/comp.text.tex/kuOEIQIrElc/lUg37FmhA74J>
newcommandUD@CheckWhetherNull[1]%
 romannumeral0expandafterUD@secondoftwostringexpandafter
 UD@secondoftwoexpandafterexpandafterstring#1expandafter
 UD@secondoftwostringexpandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@secondoftwoexpandafterexpandafterUD@firstoftwo UD@firstoftwo%
%
%%-----------------------------------------------------------------------------
%% Check whether argument's first token is a catcode-1-character
%%.............................................................................
%% UD@CheckWhetherBrace<Argument which is to be checked>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has leading
%% catcode-1-token>%
%% <Tokens to be delivered in case that argument
%% which is to be checked has no leading
%% catcode-1-token>%
newcommandUD@CheckWhetherBrace[1]%
 romannumeral0expandafterUD@secondoftwoexpandafterexpandafter%
 string#1.expandafterUD@firstoftwoexpandafterexpandafter
 UD@secondoftwostringexpandafterexpandafterUD@firstoftwo %
 UD@firstoftwoexpandafterexpandafterUD@firstoftwo UD@secondoftwo%
%
%%=============================================================================
%% macroc for processing one argument within which
%% you may have one or two or three brace-nested arguments:
%%-----------------------------------------------------------------------------
newcommandmacrocatonearg[1]C_#1%
newcommandmacrocattwoargs[2]C_#1^[#2]%
newcommandmacrocatthreeargs[3]C_#1,#3^[#2]%
newcommandmacrocatsyntaxerror%
 @latex@errorIncorrect SyntaxSpecify either one or two or three arguments that are nested in braces.%
%
newcommandmacroc[1]%
 UD@CheckWhetherBrace#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobble#1%
 macrocatonearg#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobble#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobbletwo#1%
 macrocattwoargs#1%
 %
 expandafterUD@CheckWhetherBraceexpandafterUD@gobbletwo#1%
 expandafterUD@CheckWhetherNullexpandafterUD@gobblethree#1%
 macrocatthreeargs#1%
 macrocatsyntaxerror%
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
 %
 macrocatsyntaxerror%
%
makeatother
begindocument

verb|$macroca$|: $macroca$ bigskip

verb|$macrocab$|: $macrocab$ bigskip

verb|$macrocabc$|: $macrocabc$ bigskip

% Syntax-errors:
% 
% $macrocabcd$
%
% $macroc a$
% 
% $macroca b$
%
% $macroca$
%
% $macroc$

enddocument

share|improve this answer

edited Sep 3 at 16:02

answered Aug 31 at 17:42

Ulrich Diez

3,250414

share|improve this answer

share|improve this answer

edited Sep 3 at 16:02

edited Sep 3 at 16:02

edited Sep 3 at 16:02

answered Aug 31 at 17:42

Ulrich Diez

3,250414

answered Aug 31 at 17:42

Ulrich Diez

3,250414

answered Aug 31 at 17:42

Ulrich Diez

3,250414

3,250414

add a comment | 

add a comment | 

 

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