Write a function that returns every other element of the list

I want to write a function that can return every other element of the list like this ['a' ; 'b' ; 'c' ; 'd' ; 'e'] can return: ['a' ; 'c' ; 'e']My function can use only with predefined functions List.hd, List.tl or List.length.I wrote this but I think something wrong...

remove_half l =  let rec rm_half n l =    if l = [] then []    else      let fst = hd l in      let rest = tl l in      if n then fst :: (rm_half (not n) rest)       else (rm_half (not n) rest)   in  rm_half true l;;