Steve D'Aprano <steve+pyt...@pearwood.info> writes: > Are there language implementations which evaluate the result of map() > (or its equivalent) in some order other than the obvious left-to-right > first-to-last sequential order? Is that order guaranteed by the > language, or is it an implementation detail?
Haskell just gives back an unevaluated thunk. The elements are evaluated in whatever order you happen to use them in. Since the evaluation isn't supposed to have observable side effects, there's no way to tell the order. There are also parallel versions (Control.Parallel.Strategies.parMap etc.) and an extension that recognizes "racing stripes" on the square brackets to make list comprehensions run faster: foo = [| sqrt(x) | x <- [1.0 .. 1000.0] |] parallelizes the calculation and offloads it to a GPU or other vector processor. You might also like this old post https://donsbot.wordpress.com/2007/11/29/use-those-extra-cores-and-beat-c-today-parallel-haskell-redux/ "map" is conceptually the lifting of a function from a given type, to the type under the action of some functor. For historical reasons map only works on lists while fmap works on arbitrary functors, but they are in principle the same thing. Depending on what the functor does, the whole concept of left-to-right order might be meaningless. -- https://mail.python.org/mailman/listinfo/python-list
