recursion - Haskell Recursive Type -

i attempting create function in haskell returning resp type illustrated below in strange mix between bnf , haskell types.

elem ::= string | (string, string, resp) resp ::= [elem] 

my question (a) how define type in haskell, , (b) if there way of doing without being forced use custom constructors, e.g., node, rather using tuples , arrays.

part 1:

data elem = el string | node string string resp type resp = [elem] 

part 2: well... kinda. unsatisfying answer is: shouldn't want because doing less type safe. more direct answer elem needs it's own constructor resp defined type synonym above. however, recommend

newtype resp = resp { getelems :: [elem] } 

so can't mix random list of elems resp. gives function getelems don't have pattern matching on single constructor. newtype let's haskell know should rid of overhead of constructor during runtime there's no indirection nice.