CODEWITHSUNDEEP
stringlisthaskellcharacter
Killerfrid Hd
Killerfrid Hd

Reputation: 41

Haskell Character in String function

Hey I'm a pretty new beginner to Haskell and I am having a small problem.

I want to write a function which checks if a given character is in a given string. Here is my code :

inString :: String -> Char -> Bool 
inString [] _ = False 
inString x c = x == c
inString x:xs c = inString xs c

For me this makes perfect sense as I know that Strings are just Lists of Characters. But I am getting a Parse error in pattern : inString.

Any help would be appreciated.

Upvotes: 4

Views: 423

Answers (3)

Daniel PP Cabral
Daniel PP Cabral

Reputation: 1624

You could use the list membership function elem

Example:

ghci>'c' `elem` "cat" --returns True

Upvotes: -1

developer_hatch
developer_hatch

Reputation: 16224

You have to think in the types for each expresion:

inString :: String -> Char -> Bool 
inString [] _ = False 
inString (x::String) (c::Char) = x == c -- won't compile char and strings cannot be compared because they have different type
inString (x:xs) c = inString xs c -- add parenthesis to x:xs -> (x:xs)

So a possible way would be:

inString :: String -> Char -> Bool 
inString [] _ = False 
inString (x:xs) c = if x == c then True else inString xs c

Upvotes: 5

chepner
chepner

Reputation: 531275

The pattern has to be parenthesized:

inString (x:xs) c = inString xs c

Upvotes: 3

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