Hi Russell On 15 Feb 2008, at 21:36, roconnor@theorem.ca wrote:
On Fri, 15 Feb 2008, GHC wrote:
Comment (by igloo):
Having reread the thread, I think we are here:
We are agreed that we should add {{{ lefts :: [Either a b] -> [a] rights :: [Either a b] -> [b] }}} and that we should add a function with type {{{ [Either a b] -> ([a],[b]) }}}
Any chance of left-factoring foldMap from the above? It's funny: what's important about the [] on the left is that it's Foldable; what's important about the [] on the right is that it's Alternative. What's both? More than one candidate, but [] is a runaway winner perhaps. Curious stuff. What if we had left :: Either a b -> Maybe a right :: Either a b -> Maybe b may :: Alternative f => Maybe a -> f a and suitable other bits and pieces? I fear that foldMap ((may . left) &&& (may . right)) is a longer name than you were hoping for, but it says what it does on the tin. Cheers Conor