Is it possible to define an `\escape` command in LaTeX?
I think you just want \@namueuse.
\@nameuse{foo}becomes\foo{\@nameuse{newcommand}}{\hi}{hi}really means{\newcommand}{\hi}{hi}, which is an error. But I think it is just an error in the question, and you intended\escape{newcommand}{\hi}{hi}(without some braces).
Use
\makeatletter
\let\escape=\@nameuse
\makeatother
Or skip right into the simple definition of \@nameuse
\newcommand*\escape[1]{\csname #1\endcsname}
I can offer a macro \CsNameToCsToken:
\CsNameToCsToken{foo} → \foo .
(If this suits your needs you can replace \CsNameToCsToken by \escape. But I think the name "CsNameToCsToken" does better describe what the macro in question does.)
Syntax:
\CsNameToCsToken⟨stuff not in braces⟩{⟨NameOfCs⟩}
→
⟨stuff not in braces⟩\NameOfCs
(⟨stuff not in braces⟩ may be empty.)
Definition (in LaTeX 2ε):
\begingroup
\makeatletter
\@firstofone{%
\endgroup
\@ifdefinable\CsNameToCsToken{%
\long\def\CsNameToCsToken#1#{\romannumeral\InnerCsNameToCsToken{#1}}%
}%
\newcommand\InnerCsNameToCsToken[2]{%
\expandafter\exchange\expandafter{\csname#2\endcsname}{\z@#1}%
}%
\newcommand\exchange[2]{#2#1}%
}%
In plain-TeX
either also define
\z@, e.g., to be a macro which expands to0⟨explicit space token⟩, or to be a\dimendef-token denoting a register holding length-value 0pt,or do:
\long\def\CsNameToCsToken#1#{\romannumeral0\InnerCsNameToCsToken{#1}}% \long\def\InnerCsNameToCsToken#1#2{% \expandafter\exchange\expandafter{\csname#2\endcsname}{ #1}% <- the space before #1 must be! }% \long\def\exchange#1#2{#2#1}%
(Due to \romannumeral-expansion the result is obtained by triggering two expansion-steps, e.g., by having two "hits" with \expandafter.)
With such a macro you are not bound to specific definition commands:
\CsNameToCsToken{foo} → \foo .
\CsNameToCsToken\newcommand{foo} → \newcommand\foo .
\CsNameToCsToken\DeclareRobustCommand{foo} → \DeclareRobustCommand\foo .
\CsNameToCsToken\global\long\outer\def{foo} → \global\long\outer\def\foo .
\CsNameToCsToken\expandafter{foo}\bar → \expandafter\foo\bar .
\CsNameToCsToken\let{foo}=\bar → \let\foo=\bar .
\CsNameToCsToken\string{foo} → \string\foo .
\CsNameToCsToken\meaning{foo} → \meaning\foo .
And here is the requested \NewDocumentCommand-example:
With \NewDocumentCommand you don't really need braces surrounding the control sequence token to define.
E.g.,
\NewDocumentCommand\foo{m}{foo's argument is: #1}
is the same as
\NewDocumentCommand{\foo}{m}{foo's argument is: #1}
Therefore you can do:
\CsNameToCsToken\NewDocumentCommand{foo}... → \NewDocumentCommand\foo... .
You can as well use such a macro for defining/calling macros whose names contain spaces:
\CsNameToCsToken{foo } → \foo␣ .
\CsNameToCsToken\newcommand{foo } → \newcommand\foo␣ .
\CsNameToCsToken\DeclareRobustCommand{foo } → \DeclareRobustCommand\foo␣ .
\CsNameToCsToken\global\long\outer\def{foo } → \global\long\outer\def\foo␣ .
\CsNameToCsToken\expandafter{foo }\bar → \expandafter\foo␣\bar .
\CsNameToCsToken\let{foo }=\bar → \let\foo␣=\bar .
\CsNameToCsToken\string{foo } → \string\foo␣ .
\CsNameToCsToken\meaning{foo } → \meaning\foo␣ .
You can also nest the calls of \CsNameToCsToken:
Example 1:
\CsNameToCsToken\CsNameToCsToken\expandafter{f o o }{b a r }
Processing the first \CsNameToCsToken yields:
\CsNameToCsToken\expandafter\f␣o␣o␣{b a r } .
Processing the second \CsNameToCsToken yields:
\expandafter\f␣o␣o␣\b␣a␣r␣ .
(Analogously: \CsNameToCsToken\CsNameToCsToken\let{f o o }={b a r } → \let\f␣o␣o␣=\b␣a␣r␣.)
Example 2:
\CsNameToCsToken\CsNameToCsToken\CsNameToCsToken\expandafter\expandafter\expandafter{f o o }\expandafter{b a r }{c r a z y }
Processing the first \CsNameToCsToken yields:
\CsNameToCsToken\CsNameToCsToken\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter{b a r }{c r a z y } .
Processing the second \CsNameToCsToken yields:
\CsNameToCsToken\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣{c r a z y } .
Processing the third \CsNameToCsToken yields:
\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣\c␣r␣a␣z␣y␣ .
Example 3:
In expansion contexts you can use \romannumeral-expansion in order to keep things going.
\romannumeral\CsNameToCsToken\CsNameToCsToken\CsNameToCsToken\z@\expandafter\expandafter\expandafter{f o o }\expandafter{b a r }{c r a z y }
\romannumeral triggers expansion until TeX has found a sequence of tokens that forms a ⟨number⟩-quantity. In the end TeX will find the ⟨number⟩-quantity \z@ whose value is 0 while with non-positive numbers \romannumeral silently swallows the tokens forming the ⟨number⟩-quantity while not delivering any token at all:
%\romannumneral-expansion in progress
\CsNameToCsToken\CsNameToCsToken\CsNameToCsToken\z@\expandafter\expandafter\expandafter{f o o }\expandafter{b a r }{c r a z y }
Processing the first \CsNameToCsToken yields:
%\romannumneral-expansion in progress
\CsNameToCsToken\CsNameToCsToken\z@\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter{b a r }{c r a z y } .
Processing the second \CsNameToCsToken yields:
%\romannumneral-expansion in progress
\CsNameToCsToken\z@\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣{c r a z y } .
Processing the third \CsNameToCsToken yields:
%\romannumneral-expansion in progress
\z@\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣\c␣r␣a␣z␣y␣ .
Now \romannumeral finds \z@, i.e., the number 0 (in a way where no further digits and no to be discarded space-token terminating the ⟨number⟩ will be searched). Therefore \romannumeral-expansion gets aborted and \romannumeral won't deliver any token:
\expandafter\expandafter\expandafter\f␣o␣o␣\expandafter\b␣a␣r␣\c␣r␣a␣z␣y␣ .
Be aware that \CsNameToCsToken internally applies \csname while applying \csname as a side effect yields assigning the control sequence in question the meaning of the \relax-primitive in case the control sequence in question was undefined before applying \csname. That assignment will be restricted to the current scope even if the \globaldefs-parameter had a positive value at the time of applying \csname.