ocharles

Magic

It’s folklore that if you’re summing a list of numbers, then you should always use strict foldl. Is that really true though? foldr is useful for lists when the function we use is lazy in its second argument. For (+) :: Int -> Int -> Int this is tyically not the case, but in some sense that’s because Int is “too strict”. An alternative representation of numbers is to represent them inductively. If we do this, sumation can be lazy, and foldr can do things that foldl simply can’t!

First, let’s define natural numbers inductively, and say how to add them:

data Nat = Zero | OnePlus Nat deriving Show

one :: Nat

rebcabin

In https://github.com/ekmett/lens/wiki/Derivation, we see some types for
composition of compositions: (.).(.), (.).(.).(.), and so on. Let's prove that
the type of (.).(.) is (a -> b) -> (c -> d -> a) -> c -> d -> b, as stated in
the site. We'll stick with prefix notation, meaning that we want the type of
(.)(.)(.).

Recall the type of composition. This should be intuitive:

  (.) :: (b -> c) -> (a -> b) -> a -> c                                      [1]

jFransham

Achieving warp speed with Rust

Contents:

• Number one optimization tip: don't
• Never optimize blindly
• Don't bother optimizing one-time costs
• Improve your algorithms
• CPU architecture primer
• Keep as much as possible in cache
• Keep as much as possible in registers