For multi-dimensional arrays, the current best option in Haskell, in my view, is repa. Repa provides high performance, regular, multi-dimensional, shape polymorphic parallel arrays. All numeric data is stored unboxed. Functions written with the Repa combinators are automatically parallel provided you supply +RTS -Nwhatever on the command line when running the program. Recently, it has … Read more
It’s hard to understand higher-rank polymorphism unless you study System F directly, because Haskell is designed to hide the details of that from you in the interest of simplicity. But basically, the rough idea is that polymorphic types don’t really have the a -> b form that they do in Haskell; in reality, they look … Read more
This looks like it fits the bill in the style of Why’s Poignant Guide to Ruby. Learn You a Haskell for Great Good!
If we compare the types (<*>) :: Applicative a => a (s -> t) -> a s -> a t (>>=) :: Monad m => m s -> (s -> m t) -> m t we get a clue to what separates the two concepts. That (s -> m t) in the type of (>>=) … Read more
This is a known bug. and a good catch! The pull request https://github.com/haskell/haskell-mode/pull/1116/files solves it.
The evaluation mechanism in Haskell is by-need: when a value is needed, it is calculated, and kept ready in case it is asked for again. If we define some list, xs=[0..] and later ask for its 100th element, xs!!99, the 100th slot in the list gets “fleshed out”, holding the number 99 now, ready for … Read more
The true quicksort has two beautiful aspects: Divide and conquer: break the problem into two smaller problems. Partition the elements in-place. The short Haskell example demonstrates (1), but not (2). How (2) is done may not be obvious if you don’t already know the technique!
Look here, the operator used is !!. I.e. [1,2,3]!!1 gives you 2, since lists are 0-indexed.
(The following applies to GHC, other compilers may use different storage conventions) Rule of thumb: a constructor costs one word for a header, and one word for each field. Exception: a constructor with no fields (like Nothing or True) takes no space, because GHC creates a single instance of these constructors and shares it amongst … Read more
From a technical standpoint, all three versions are equivalent. That being said, my rule of thumb for styles is that if you can read it as if it was English (read | as “when”, | otherwise as “otherwise” and = as “is” or “be”), you’re probably doing something right. if..then..else is for when you have … Read more