The trick is explicitly stating the return type.
(I also explicitly defined the input type in this 
example as well.)


fun charListToIntList(L: char list) : int list = 
  if L = nil then
    nil
  else
    [ord(hd(L))] @ charListToIntList(tl(L))
;


- charListToIntList([#"A", #"l", #"a", #"n"]);
val it = [65,108,97,110] : int list