What does Weak Head Normal Form (WHNF) mean? What does Head Normal form (HNF) and Normal Form (NF) mean? Real World Haskell states: The familiar seq function evaluates an expression to what we call head normal form (abbreviated HNF). It stops once it reaches the outermost constructor (the “head”). This is distinct from normal form (NF), in which an expression is … Read more
Haskell (with the GHC compiler) is a lot faster than you’d expect. Used correctly, it can get close-ish to low-level languages. (A favorite thing for Haskellers to do is to try and get within 5% of C (or even beat it, but that means you are using an inefficient C program, since GHC compiles Haskell … Read more
Here’s the scenario: I’ve written some code with a type signature and GHC complains could not deduce x ~ y for some x and y. You can usually throw GHC a bone and simply add the isomorphism to the function constraints, but this is a bad idea for several reasons: It does not emphasize understanding … Read more
I’m trying to implement a neural network architecture in Haskell, and use it on MNIST. I’m using the hmatrix package for linear algebra. My training framework is built using the pipes package. My code compiles and doesn’t crash. But the problem is, certain combinations of layer size (say, 1000), minibatch size, and learning rate give … Read more
I have heard the term “coalgebras” several times in functional programming and PLT circles, especially when the discussion is about objects, comonads, lenses, and such. Googling this term gives pages that give mathematical description of these structures which is pretty much incomprehensible to me. Can anyone please explain what coalgebras mean in the context of … Read more
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I’m beginning to understand how the forall keyword is used in so-called “existential types” like this: data ShowBox = forall s. Show s => SB s This is only a subset, however, of how forall is used and I simply cannot wrap my mind around its use in things like this: runST :: forall a. … Read more
From the docs for GHC 7.6: [Y]ou often don’t even need the SPECIALIZE pragma in the first place. When compiling a module M, GHC’s optimiser (with -O) automatically considers each top-level overloaded function declared in M, and specialises it for the different types at which it is called in M. The optimiser also considers each … Read more
In my humble opinion the answers to the famous question “What is a monad?”, especially the most voted ones, try to explain what is a monad without clearly explaining why monads are really necessary. Can they be explained as the solution to a problem? 8 Answers 8
I’ve seen the term Free Monad pop up every now and then for some time, but everyone just seems to use/discuss them without giving an explanation of what they are. So: what are free monads? (I’d say I’m familiar with monads and the Haskell basics, but have only a very rough knowledge of category theory.) … Read more
