Types (or classes) of Haskell functions

edit: my new site is here: https://thaumatorium.com/

Slightly annoying that type and class already have a certain meaning in Haskell, but I think you’re smart enough to understand what I mean with the Title

In this context, a parser is a function accepting strings as input and returning some structure as output, typically a parse tree or a set of indices representing locations in the string where parsing stopped successfully.

Function typename	What it does	Example code
Pure	Takes an input, returns an output – no side effects (data changes)	f :: Int -> Int f x = x
Predicate	Takes an input, returns a Bool	f :: Int -> Bool f x = x > 5
Recursive	Like a Pure function, but also calls itself (at least once) with a subset of the original input	length :: [a] -> Int length (x:xs) = 1 + length xs
Curried	You can give a function a part of the input to create a new function ( imperative languages like C or Python always want all arguments at once)	timesTwo :: Int -> Int timesTwo = 2 * As you can see, the * operator only has one input – It’s been partially applied! When you look at the definition, you see that timesTwo expects at least one Int, which when applied, gets added at the end of the function: timesTwo 3 = { apply timesTwo } 2 * 3 = { apply * } 6
Applicative	Can take a variable amount of inputs, returns an output	Uses a function (pure) and an operator (<*>), where ‘pure’ lifts the function into a wrapped type/function and ‘<*>’ accepts a wrapped type/function and a variable (that’s also wrapped)
Monadic	Takes an input, returns an output – has side effects (data changes) and uses either the bind >>= operator or do notation	From: https://wiki.haskell.org/All_About_Monads maternalGrandfather :: Sheep -> Maybe Sheep maternalGrandfather s = (return s) >>= mother >>= father -- alternatively mothersPaternalGrandfather :: Sheep -> Maybe Sheep mothersPaternalGrandfather s = do m <- mother s gf <- father m father gf
Parser Combinator	Accepts several parsers as input and returns a new parser as its output.	From: https://en.wikipedia.org/wiki/Parser_combinator In this context, a parser is a function accepting strings as input and returning some structure as output, typically a parse tree or a set of indices representing locations in the string where parsing stopped successfully.

edit: my new site is here: https://thaumatorium.com/