— CISC 360 Fall 2022
— Week 7, part 3
Copyright By PowCoder代写 加微信 powcoder
module Lec16 where
“Continuations” are a particular way of using higher-order functions.
This file contains two versions of a function that searches for a character in a string,
and returns all the positions at which the character occurs.
Positions are counted from zero.
For example:
stringfind ‘a’ “cadar” == [1, 3]
stringfind ‘z’ “cadar” == []
stringfind :: Char -> String -> [Integer]
stringfind ch s = stringfind_help 0 ch s
— stringfind_help n ch s:
— Return the positions at which ch occurs in s, WITH n ADDED.
stringfind_help :: Integer -> Char -> String -> [Integer]
stringfind_help n ch [] = []
stringfind_help n ch (h : t) =
(if ch == h then [0 + n] else []) ++ stringfind_help (n + 1) ch t
add1 = map ((+) 1)
kstringfind_help :: Char
-> ([Integer] -> [Integer])
-> [Integer]
kstringfind_help ch [] k = k []
kstringfind_help ch (h : t) k =
if ch == h then kstringfind_help ch t (\list -> k (0 : add1 list))
else kstringfind_help ch t (\list -> k (add1 list))
kstringfind :: Char -> String -> [Integer]
kstringfind ch s = kstringfind_help ch s (\list -> list)
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