Can i call macros something like this


So, i would like to have running window of length 3. And for this end i would like to be able to use temporary unnamed local variable \X+2 as i can in C++.

  • 1
    Sorry, but it's very unclear what your aim is. – egreg Apr 24 '17 at 11:18
  • @egreg Op wishes, given a string, to be able to extract and display a substring (a window into the string). This substring should be specified by its start index and length, as opposed to start/end indices, using the \StrMid command from xstring package. – marsupilam Apr 24 '17 at 13:02

You can use \numexpr\X+2 in order to evaluate the number of the end-'index' here.

Of course \numexpr\foo+\foobar will be an even more flexible solution.

Since \StrMid is not expandable the usability of \StrMid depends on the real design.



\def\mystring{And now for something completely different}


This yields or something c here.

|improve this answer|||||
  • @StevenB.Segletes: ;-) You should look for many other answers of mine having MP references -- you will get a lot of upvotes to be done then :D – user31729 Apr 24 '17 at 11:12
  • 1
    It's not meant to be taken literally. [Obviously it refers to any manufacturers of dairy products.] – Steven B. Segletes Apr 24 '17 at 11:16
  • @StevenB.Segletes: What a pity/shame :D – user31729 Apr 24 '17 at 11:56

A fully expandable function, with the help of expl3:


  \tl_map_function:fN { \tl_range:onn { #1 } { #2 } { #3 } } \use:n
\cs_generate_variant:Nn \tl_map_function:nN { f }
\cs_generate_variant:Nn \tl_range:nnn { o }






The second and third argument of \stringwindow can be any integer denotation, that is, also counter registers, such as \value{chapter}, besides macros that expand to numbers.

Note: spaces are not preserved. A slower routine would be needed for this.

enter image description here

|improve this answer|||||

Here's a LuaLaTeX-based solution. Note that the macro \StrMid is fully expandable. All three arguments of \StrMid may consist of (or contain) macros; the only requirement is that the args evaluate to either a string (the first arg) or integers (the second and third arg). And, the result of \StrMid may be assigned to a new macro.

enter image description here

% !TeX program = lualatex
\usepackage{luacode} % for "\luastring" macro


\newcommand\foo{2+2} % something that evaluates to an integer in Lua 

\StrMid{\mystring}{\foo}{\foo+2} % returns "now"

% assign result of \StrMid to a LaTeX macro:
\bbar % returns "let"
|improve this answer|||||

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.