EOPL - 2.3.3 - Exercise 2.19

Another simple exercise.

// Exercise 2.19
type 'a Stack = EmptyStack | ExtendedStack of 'a * 'a Stack

let empty_stack () = 
    EmptyStack
    
let push elt stk = 
    ExtendedStack (elt, stk)
    
let pop stk = 
    match stk with
      EmptyStack -> failwith "Stack empty"
    | ExtendedStack (_, s) -> s
    
let top stk = 
    match stk with
      EmptyStack -> failwith "Stack empty"
    | ExtendedStack (e, _) -> e
    
let is_stack_empty stk = 
    stk = EmptyStack