Is there a LaTeX3 equivalent for \@ifpackageloaded?

Question

Is there a LaTeX3 equivalent for \@ifpackageloaded?

Answer 1

No, there isn't. But you can easily build it.

\prg_new_conditional:Nnn \mhchem_package_if_loaded:n { p, T, F , TF }
 {
  \use:c { @ifpackageloaded } { #1 } { \prg_return_true: } { \prg_return_false: }
 }

This will define the conditionals

\mhchem_package_if_loaded:nTF
\mhchem_package_if_loaded:nT
\mhchem_package_if_loaded:nF

and the predicate form

\mhchem_package_if_loaded_p:n

to be used in boolean expressions.

A test:

\documentclass{article}
\usepackage{expl3}

\ExplSyntaxOn

\prg_new_conditional:Nnn \mhchem_package_if_loaded:n { p, T, F , TF }
 {
  \use:c { @ifpackageloaded } { #1 } { \prg_return_true: } { \prg_return_false: }
 }

% now let's test it

\mhchem_package_if_loaded:nTF { expl3 }
 { \typeout{Yes~expl3} }
 { \typeout{No~expl3} }

\mhchem_package_if_loaded:nT { expl3 }
 { \typeout{Yes~expl3} }

\mhchem_package_if_loaded:nTF { kantlipsum }
 { \typeout{Yes~kantlipsum} }
 { \typeout{No~kantlipsum} }

\mhchem_package_if_loaded:nF { kantlipsum }
 { \typeout{No~kantlipsum} }

\bool_if:nTF
 {
  \mhchem_package_if_loaded_p:n {expl3}
  ||
  \mhchem_package_if_loaded_p:n {kantlipsum}
 }
 { \typeout{Yes~expl3~or~kantlipsum} }
 { \typeout{No~expl3~or~kantlipsum} }

\bool_if:nTF
 {
  \mhchem_package_if_loaded_p:n {expl3}
  &&
  \mhchem_package_if_loaded_p:n {kantlipsum}
 }
 { \typeout{Yes~expl3~and~kantlipsum} }
 { \typeout{No~expl3~and~kantlipsum} }

\stop

The relevant console output:

Yes expl3
Yes expl3
No kantlipsum
No kantlipsum
Yes expl3 or kantlipsum
No expl3 and kantlipsum