GHC has a lot of optimizations that it can perform, but I don’t know what they all are, nor how likely they are to be performed and under what circumstances. My question is: what transformations can I expect it to apply every time, or nearly so? If I look at a piece of code that’s … Read more
Core is GHC’s intermediate language. Reading Core can help you better understand the performance of your program. Someone asked me for documentation or tutorials on reading Core, but I couldn’t find much. What documentation is available for reading GHC Core? Here’s what I’ve found so far: Write Haskell as fast as C: exploiting strictness, laziness … Read more
I’ve recently posted a question about syntactic-2.0 regarding the definition of share. I’ve had this working in GHC 7.6: {-# LANGUAGE GADTs, TypeOperators, FlexibleContexts #-} import Data.Syntactic import Data.Syntactic.Sugar.BindingT data Let a where Let :: Let (a :-> (a -> b) :-> Full b) share :: (Let :<: sup, sup ~ Domain b, sup ~ … 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 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
