palindrome
From TidalCycles userbase
Type: palindrome :: Pattern a -> Pattern a
The palindrome function applies rev to a pattern every other cycle, so that the pattern alternates between forwards and backwards.
For example this:
d1 $ palindrome $ sound "arpy:0 arpy:1 arpy:2 arpy:3"
... is the same as this:
d1 $ slow 2 $ sound "arpy:0 arpy:1 arpy:2 arpy:3 arpy:3 arpy:2 arpy:1 arpy:0"
... and indeed this:
d1 $ every 2 rev $ sound "arpy:0 arpy:1 arpy:2 arpy:3"