// F# versions of some C# programs.
// Compile program to .exe with fsc exptree.fs
// To run in interactive console, type  #load "c:\\..path..\\filename";;

open System

// food list 

type food = Fruit of int | Veg of int*string | Meat of int*int;;
type flist = Nofood | Cons of food*flist;;

let car = function
  | Cons(a,b) -> a;   // this is an incomplete definition - automatically
                      // throws exception.

let cdr = function
  | Nofood -> Nofood
  | Cons(a,b) -> b;

let myfood = Cons(Fruit(50),Cons(Veg(100,"green"),Cons(Meat(200,1),Nofood)));

Console.WriteLine(car(myfood));

// function to add up all the calories
let rec cals = function
  | Nofood -> 0
  | Cons(Veg(x,y),t) -> x + cals(t)
  | Cons(Fruit(x),t) -> x + cals(t)
  | Cons(Meat(x,_),t) -> x + cals(t);;

// function to test if food list is ordered fruit-veg-meat.
// I wrote this using a variety of styles.

type foodstate = Fstate | Vstate | Mstate;;

let rec ordered = function
| (state,  Cons(Fruit(_),t)) -> 
     not(state=Vstate || state=Mstate) && ordered(Fstate,t);
| (Mstate, Cons(Veg(_,_),t)) -> false;
| (_,      Cons(Veg(_,_),t)) -> ordered(Vstate,t);
| (_,      Cons(Meat(_,_),t)) -> ordered(Mstate,t);
| (_,Nofood) -> true;;   // note two ; here

Console.WriteLine("is ordered? " + string(ordered(Fstate,myfood)));;