Re: [Haskell-cafe] Arrows for invertible programming: Notation question

What does this mean and how do I make it compile?

mapl{|a, b|arr|} :: (mapl{|a, b|arr|}, ArrowChoice arr, BiArrow arr) => arr a b

It's Generic Haskell source code, see http://www.generic-haskell.org/ Generic Haskell is an extension of Haskell that supports generic programming. Cheers, Ralf