Haskell99题答案

1 Problem 1

(*) Find the last element of a list.

(Note that the Lisp transcription of this problem is incorrect.)

Example in Haskell

Prelude> myLast [1,2,3,4]4Prelude> myLast ['x','y','z']'z'

答案

run::[a]->arun [x]=xrun (_:xs) = run xs

run = foldl (const id)

对于上述的代码，有如下的解释

const id True 2= (const id True) 2= id 2= 2

如果要保留第一个，可以用如下的代码

foldl1 const [1,2,3,4]