Haskell string/output manipulation

Question

I do have the following code:

suffixes :: [a] -> [[a]]
suffixes [] = [[]]
suffixes l@(_:t) = l : suffixes t

prefixes :: [a] -> [[a]]
prefixes [] = [[]]
prefixes l@x = l : prefixes (init x)

menu :: Char -> [a] -> Either String [[a]]
menu 'p' l = Right (prefixes l)
menu 's' l = Right (suffixes l)
menu x _ = Left ("(" ++ show x ++ ")" ++ "is not supported, use (p)refix or (s)uffix")

I do have the following test function:

testMenuP = "Expected Right [[1,2],[1],[]]; menu 'p' [1,2] returned " ++ show (menu 'p' [1,2] :: Either String [[Int]])

testMenuS = "Expected Right [[1,2],[2],[]]; menu 's' [1,2] returned " ++ show (menu 's' [1,2] :: Either String [[Int]])

testMenuC = "Expected Left \"(d) is not supported, use (p)refix or (s)uffix\"; menu 'd' [1,2] returned " ++ show (menu 'd' [1,2] :: Either String [[Int]])

testMenu = putStr (testMenuP ++ "\n" ++ testMenuS ++ "\n" ++ testMenuC ++ "\n")

My question is now, how do I get rid of the quotes '' in the Char 'd' when I output the string (as shown in the test function testMenuC).

I think your question could be replaced with: show 'c' returns "'c'", how do I get "c" instaed? Or How do I convert a Char to a String. And the answer would be: use ['c'] instead of show 'c'. — Micha Wiedenmann
– Micha Wiedenmann, Commented Oct 27, 2021 at 9:07
Please remove the code that is not absolutely important. This makes it easier to spot your question. — Micha Wiedenmann
– Micha Wiedenmann, Commented Oct 27, 2021 at 9:08

cstml · Accepted Answer · 2021-10-27 09:34:25Z

2

You can replace the part of menu with:

menu x _ = Left ("(" ++ [x] ++ ")" ++ "is not supported, use (p)refix or (s)uffix")

or even

menu x _ = Left . mconcat $ ["(", [x], ")", "is not supported, use (p)refix or (s)uffix"]

answered Oct 27, 2021 at 9:34

cstml

3902 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Haskell string/output manipulation

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related