On Tue, May 3, 2011 at 1:32 AM, Manuel M T Chakravarty
... Interestingly, today (at least the academic fraction of) the Haskell community appears to hold the purity of the language in higher regard than its laziness.
As someone who implemented Haskell with quite a bit less laziness, I'm inclined to agree. That said, I think it's easy to underestimate just how much of the structure of the language really encourages a lazy evaluation strategy. One example: where blocks scope over groups of conditional RHSs. This is very handy, in that we can bind variables that are then used in some, but not all, of the disjuncts. Grabbing the first example that comes to hand from my own code: tryOne (gg, uu) e | not (consistent uu) = (gg', uu) | uu==uu' = (gg, uu) | otherwise = (gg', uu') where gg' = gg `addEquation` e uu' = uu `addEquation` e This kind of thing happens all over the place in Haskell code -- it's a very natural coding style -- but if you want to preserve purity it's tough to compile without laziness. -Jan-Willem Maessen