» CS 330 Lecture 32 – Type Inference, Functions, and Lists

CS 330 Lecture 32 – Type Inference, Functions, and Lists

April 18, 2014 by Chris Johnson. Filed under cs330, lectures, spring 2014.

Agenda

what ?s
type interference in other languages
type signatures
curried functions
infinite lists
list processing
- case statements
- pattern matching
- map
- lambda

Think About This

Someone hands you a number k and an arbitrary list of size n. The someone demands, “What’s the kth smallest element?” Assume 0 <= k < n. What do you do?

Someone hands you a number k. The someone demands, “What’s the kth smallest element?” What do you do?

Code

april18.hs

import Data.List

initials :: String -> String -> String -> String
initials first second third = head first : head second : head third : []

kth :: Int -> [Int] -> Int
kth k items = sort items !! k

best :: [Int] -> Int
best = kth 0

runnerup :: [Int] -> Int
runnerup = kth 1

sum' :: [Int] -> Int
-- sum' ns =  
  -- case ns of 
    -- [] -> 0 
    -- (first:rest) -> first + sum' rest 
sum' [] = 0
sum' (first:rest) = first + sum' rest

convertMilesToKilometers [] = []
convertMilesToKilometers (first:rest) = (1.609 * first) : convertMilesToKilometers rest

needsOurLove :: [(String, String)] -> [Bool]
needsOurLove [] = []
needsOurLove ((_, lastName):rest) = (head lastName >= 'N') : needsOurLove rest

Haiku

Nerds learn fast, mostly
Part of Haskell trips them up
The social functions