@( ) inconsistent

[ixemad]

Hi!

I'm playing with xonsh and this contrib is really useful to leverage it.

I detected some inconsistencies with the experimental feature @(). The following can help polish it.

The ls | pl @( line ) works as it's expected but not ls | pl @( line.upper() ). However, ls | pl @( (lambda l: l.upper())(line) ) does.

[anki-code]

Hi @ixemad! Thank you for catching this! PR with fix is welcome!
If you like the contrib please star the repo to put it to the trends and get more attention from xonsh maintainers and folks.