Haskell: Non-exhaustive patterns in function (simple functions) -

Haskell: Non-exhaustive patterns in function (simple functions) -

i confused why 1st , 3rd versions of functions give error whereas sec definition works fine.

-- head , tail 3rd :: [a] -> 3rd [a] = head (tail (tail[a])) -- pattern matching third2 :: [a] -> third2 (_:_:x:_) = x -- list indexing third3 :: [a] -> third3 [a] = [a]!!2

thanks in advance

that odd sec 1 not complain non-exhaustive patterns, since third2 not match lists of length zero, one, or two. third , third3 functions complain because [a] not variable, pattern. [a] desugars (a:[]), have written them as

third (a:[]) = head (tail (a:[])) third3 (a:[]) = (a:[]) !! 2

neither of work, single element lists. suspect want is

third = head (tail a) third3 = !! 2

haskell non-exhaustive-patterns