3 Sep
2013
3 Sep
'13
9:48 p.m.
allPairs2 can be simplified using a trick I wouldn't dare use in any language but Haskell: triangle4 xs = fused undefined [] xs where fused x (y:ys) zs = (x,y) : fused x ys zs fused _ [] (z:zs) = fused z zs zs fused _ [] [] = [] I submit this just for grins; it happens to be a touch faster but not enough to bother about. While the result _isn't_ all possible pairs of elements, making the allPairs name a bit dodgy, it _does_ have O(|xs|**2) of them... I would be surprised if the relative performance of two approaches in ghci were always the same as their relative performance in ghc.