CODEWITHSUNDEEP
haskellrecursion
Ethan Lim
Ethan Lim

Reputation: 93

How to delete the last character in a string (without using init) in Haskell?

I'm really new to Haskell programming. Can anyone help with this issues? -- delete the last character from a string in Haskell

deleteLast []     = "Empty list!" -- if the string is enpty 
deleteLast (h:[]) = h  -- recursion
deleteLast (h:t)  = deleteLast t -- found the last character
result1 = [x | x == deleteLast , x /= deleteLast t] -- trying to remove the last character found 
                                                       from the string

Upvotes: 1

Views: 3098

Answers (2)

Ethan Lim
Ethan Lim

Reputation: 93

myLast :: [a] -> [a]
myLast []     = error "Empty list!"
myLast [h]    = []
myLast (h:t)  =[h]++myLast t

Output:
ghci> myLast "pineapple"
"pineappl"
ghci> myLast "pen"
"pe"

Thanks for the tips. @William Van Onsem

Upvotes: 2

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476557

The return type of the deleteLast is the same type as the item of the list. Indeed, the second clause specfies:

deleteLast (h:[]) = h

here h is the head of the list, and thus the first item. The pattern (h:[]) is equivalent to [h], so this fires if there is a list with one element. In that case we return that singe element.

In case a list contains one element, we have to remove that element from the list (1). If we work with a list with at least two elements, we should yield the first item of that list, and recurse on the tail of the list:

deleteLast :: [a] -> [a]
deleteLast [] = error "Empty list!"
deleteLast [h] = …  -- (1)
deleteLast (h:t) = … deleteLast t  -- (2)

I leave implementing the second and third clause as an exercise.

Upvotes: 4

Related Questions