haskell中的字符串流

Question

我正在嘗試在haskell中創建此流l = ["","a","aa","aaa",...]。

有人可以幫助我嗎？

Answer 1

[replicate i 'a' | i <- [0..]] 

這不是完全先進的東西。通過只是在做

iterate ('a':) "" 

Answer 2

結合inits與重複功能：

l = l' "" 
    where l' s = s : l' ('a':s) 

Answer 3

我們只要通過反覆consing元素到空列表那裏使用

iterate :: (a -> a) -> a -> [a] 

：

Answer 4

不使用預定義

λ: let l = inits $ repeat 'a' 
λ: take 10 l 
["","a","aa","aaa","aaaa","aaaaa","aaaaaa","aaaaaaa","aaaaaaaa","aaaaaaaaa"]