Searching through list of tuples

Question

I\'m trying to write a function that accepts a string and a list of tuple pairs. I want to search through the list of tuples, and if the first value in the tuple matches the inp

Answer 1

In the base case, if list is empty, it returns Nothing. Then, if first element a of tuple in the head is equal to element x, it returns second element Just b. Else, recursively, it searchs in the tail.

search :: (Eq a) => a -> [(a,b)] -> Maybe b
search _ [] = Nothing
search x ((a,b):xs) = if x == a then Just b else search x xs

You can implement an unsafe version without Maybe:

search :: (Eq a) => a -> [(a,b)] -> b
search _ [] = error "element not found"
search x ((a,b):xs) = if x == a then b else search x xs

Other option is searching a list instead of first ocurrence, then, empty list [] is equivalent to Nothing:

search :: (Eq a) => a -> [(a,b)] -> [b]
search x = map snd . filter ((==x).fst)