George Lukas george-lukas

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abhin4v / astar.hs

Last active November 24, 2022 06:36

A* (A star) search in haskell

	import qualified Data.PQueue.Prio.Min as PQ
	import qualified Data.HashSet as Set
	import qualified Data.HashMap.Strict as Map
	import Data.Hashable (Hashable)
	import Data.List (foldl')
	import Data.Maybe (fromJust)

	astarSearch :: (Eq a, Hashable a) => a -> (a -> Bool) -> (a -> [(a, Int)]) -> (a -> Int) -> Maybe (Int, [a])
	astarSearch startNode isGoalNode nextNodeFn heuristic =
	astar (PQ.singleton (heuristic startNode) (startNode, 0))

animatedlew / len.hs

Last active April 16, 2024 14:09

Here are two ways to implement Haskell's length function. One way is to map all the elements to 1, then sum them all up. Another way is to add up each head as you recursively call len' with the tail. The result will be the length of the list.

	-- Maps each element to a 1, then sums up all the elements
	len :: [a] -> Integer
	len = sum . map (\_ -> 1)

	-- Adds up all the heads (recursively) until the list is empty
	len' :: [a] -> Integer
	len' [] = 0
	len' (_:xs) = 1 + len' xs

	-- Extract into a fold using this technique: [ [] := v, (:) := f ]