Johannes Krause cjay

List folds in Haskell from a use case oriented perspective

Since the definitions in Data.Foldable are too generic, here are list-specific ones:

-- foldl f z [x1, x2, ..., xn] == (...((z `f` x1) `f` x2) `f`...) `f` xn
foldl :: (b -> a -> b) -> b -> [a] -> b
foldl f z []     = z
foldl f z (x:xs) = let z' = z `f` x
                   in foldl f z' xs

	{-# LANGUAGE RankNTypes #-}
	import Control.Monad.Cont (MonadIO)

	-- Comparison: How simplified subsumption interacts with newtype and with type aliases

	-- example with type alias:

	type Foo a = forall m. MonadIO m => m a

	foo :: forall m a. MonadIO m => Int -> m a

	/*
	For use with the Stylus browser extension, since Dark Reader is slow on the giant single page spec.
	*/

	html,
	body,
	input,
	textarea,
	select,
	button {

	{-# LANGUAGE FlexibleContexts #-}
	{-# LANGUAGE KindSignatures #-}
	{-# LANGUAGE TypeFamilies #-}
	{-# LANGUAGE TypeOperators #-}
	{-# LANGUAGE NoStarIsType #-}
	{-# LANGUAGE UndecidableInstances #-}
	{-# LANGUAGE AllowAmbiguousTypes #-}
	{-# LANGUAGE PolyKinds #-}
	{-# LANGUAGE RankNTypes #-}
	{-# LANGUAGE ConstraintKinds #-}

	Mon Jan 21 18:31 2019 Time and Allocation Profiling Report (Final)

	day14b +RTS -p -RTS

	total time = 18.53 secs (18528 ticks @ 1000 us, 1 processor)
	total alloc = 46,140,950,288 bytes (excludes profiling overheads)

	COST CENTRE MODULE SRC %time %alloc

	generate.gen Main src/Day14b.hs:(83,3)-(91,34) 24.1 36.0