Also in Haskell [0]:

    (|>) :: Seq a -> a -> Seq a
    O(1). Add an element to the right end of a sequence. Mnemonic: a triangle with the single element at the pointy end. 

It seems to be in the containers package since 2005: [1]

[0]: http://hackage.haskell.org/package/containers-0.5.5.1/docs/D...

[1]: https://github.com/haskell/containers/commit/1e61853dbd4b9fc...