expl3 expressions and returns

Question

In my attempts to get grasp on expl3 I have come into a wall, I cannot figure out how store the result of a function.

For example in pseudocode of what I want to do is this, store the second character of tempstring (that is the character b) in otherstring without changing tempstring

string tempstring = abcde
string otherstring = tempstring[2]

print tempstring
print otherstring

This would result in the output of abcde b

In the following expl3 code I believe I have declared my variables correctly, but the 4th line where I do my operation does not work.

\tl_new:N \templist
\tl_new:N \otherlist

\tl_set:Nn \templist {abcde}
\tl_set:Nn \otherlist {\tl_item:Nn \templist {2}}
\templist
\otherlist

I would have expected this to output abcde b as well but it does not.

And unfortunately \otherlist = \templist doesn't seem to do what I need either.

I have also tried \tl_set_eq:Nn \otherlist {\tl_item:Nn \templist {2}} but that doesn't work either.

---

I have edited the code to show a minimal broken example, apparently what I wrote above works just fine.

Edited again, I found my error. David was correct. In my main code I had forgotten the :Nn after \tl_item

Answer 1

The code works as you describe (it is always best to give a full document that shows an error?)

\documentclass{article}
\usepackage{expl3}
\begin{document}

\ExplSyntaxOn

\tl_new:N \templist
\tl_new:N \otherlist

\tl_set:Nn \templist {abcde}
\tl_set:Nn \otherlist {\tl_item:Nn \templist {2}}

\ExplSyntaxOff

\templist

\otherlist

\end{document}

Note that this defines \otherlist to extract the second token. If you want it to be the result of that, use

\tl_set:Nx \otherlist {\tl_item:Nn \templist {2}}

the visual output is the same, b in both cases.