expl3 empty token list

Question

Im sure this must be something very simple but it is eluding me.

The following code outputs F. Shouldn't it output T?

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

\ExplSyntaxOn


\tl_new:N \otherlist
\tl_clear_new:N \otherlist

\tl_if_empty:nTF {\otherlist} {T} {F}


\ExplSyntaxOff

\end{document}

Answer 1

The test \tl_if_empty:NTF \l_bob_otherlist_tl {}{} sees just the empty token list \l_bob_otherlist_tl, but \tl_if_empty:nTF {\l_bob_otherlist_tl} {}{} sees one token in the 'list' delimited by {...}.

See the difference for example with the \tl_count:n and \tl_count:N macros:

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

\ExplSyntaxOn


\tl_new:N \l_bob_otherlist_tl


First:  \tl_if_empty:nTF \l_bob_otherlist_tl {T} {F}
\par
Second: \tl_if_empty:NTF \l_bob_otherlist_tl {T} {F}
\par
Third: \tl_if_empty:nTF {\l_bob_otherlist_tl} {T} {F}
\par
\par
Counting~with~n: \tl_count:n {\l_bob_otherlist_tl}
\par
Counting~with~N: \tl_count:N \l_bob_otherlist_tl
\tl_set:Nn \l_bob_otherlist_tl {Foo}
\par
After~setting:\par
First:  \tl_if_empty:nTF \l_bob_otherlist_tl {T} {F}
\par
Second: \tl_if_empty:NTF \l_bob_otherlist_tl {T} {F}
\par
Third: \tl_if_empty:nTF {\l_bob_otherlist_tl} {T} {F}
\par
Counting~with~n: \tl_count:n {\l_bob_otherlist_tl}
\par
Counting~with~N: \tl_count:N \l_bob_otherlist_tl


\ExplSyntaxOff

\end{document}

The \tl_clear_new:N isn't necessary since \tl_new:N already provides an empty, clean list.