-- swaps every two elements in a list
swap :: [a] -> [a]
swap [] = []
swap [a] = [a]
swap [a,b] = [b,a]
swap [a,b,c] = [b,a,c]
swap [a,b,c,d] = [b,a,d,c]
swap [a,b,c,d,e] = [b,a,d,c,e]
swap [a,b,c,d,e,f] = [b,a,d,c,f,e]