Jonathan Lorimer JonathanLorimer

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Intro to FP Through λ-Calc Part 1. - Motivating Laziness

Jonathan Lorimer

19/03/2020

Mar 19, 2020

Introduction to Functional Programming Through Lambda Calculus gave a thorough explanation of evaluation in lambda calculus, I found this helped motivate a better understanding of evaluation in haskell!

lambda-calculus

	const productType = { a: 3, b: "hello", c: false }
	// this has the implied type data ProductType = { a :: Number, b :: String, c :: false }
	// even if javascript doesn't demand that we think about it, it matters
	// as demonstrated by the below function which IMPLICITLY expects that type signature

	const repeatWord = ({a, b, c}) => b + (c ? " " : "/n") + (a <= 0 ? "" : repeatWord({a: a - 1, b, c})
	// if you give the above function the wrong 'type' you will get unexpected behaviour
	// rather than resulting in a type error you will get either a runtime error or an unexpected return value

	// Similarly you might have this

	{-# LANGUAGE FlexibleInstances #-}
	module FunctorInstancesExercises where


	-- \| 1.
	data Quant a b = Finance
	\| Desk a
	\| Bloor b

	instance Functor (Quant a) where

	module FunctorInstances where

	import Test.QuickCheck

	newtype Identity a = Identity a
	deriving (Eq, Show)

	instance Functor Identity where
	fmap f (Identity a) = Identity (f a)

	<!DOCTYPE HTML>
	<html>
	<head>
	<style>
	body {
	margin: 0px;
	padding: 0px;
	}
	</style>
	</head>

Jonathan Lorimer JonathanLorimer

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