Recursive functions that reverse a list in Haskell -

i've been tasked create recursive function takes in list , gives reverse of list.

i have been able create function named rev1 this:

rev1 :: [a] -> [a]  rev1 [] = []  rev1 (x:xs) = reverse xs ++ [x]  

but have been asked create function 'rev2' should use additional argument serving accumulator.

could please me compose rev2 function.

thanks in advance, sam

first of all, rev1 should instead:

rev1 :: [a] -> [a]  rev1    []  = []  rev1 (x:xs) = rev1 xs ++ [x] 

the point of rev2 achieve tail recursion means of passing intermediate result inside accumulator argument:

rev2 :: [a] -> [a] -> [a] -- if applied empty list, return result -- far, i.e. whatever inside accumulator: rev2 acc    []  =         acc -- otherwise, take head of list , append -- accumulator, , carry on rest of list rev2 acc (x:xs) = rev2 (x:acc) xs 

this, however, has downside of exposing acc argument users of rev2, typical approach hiding accumulator based implementation behind façade looks rev1:

rev2 :: [a] -> [a] rev2 xs = go [] xs   go :: [a] -> [a] -> [a]  -- signature included clarity   go acc    []  =       acc   go acc (x:xs) = go (x:acc) xs