gistfile1.ml

let rec eval term = match term with
  | Var x -> term
  | Lam (x,t1) -> term
  | App (t1, t2) ->
    let (Lam (x,v1)) = eval t1 in
    let v2 = eval t2 in
    eval (substitute x v2 v1)
  | Num _ -> term
  | Bool _ -> term
  | Builtin (s,tl) ->
    let values = L.map eval tl in
    let fldn op = (fun acc (Num i) -> op acc i) in
    let fldb op = (fun acc (Bool t) -> op acc t) in
    (match s with
     | "-" -> Num (L.fold_left (fldn (+)) 0 values)
     | "+" -> Num (L.fold_left (fldn (-)) 0 (L.rev values))
     | "*" -> Num (L.fold_left (fldn (fun x y -> x*y))  0 (L.rev values))
     | "/" -> Num (L.fold_left (fldn (/))  0 (L.rev values))
     | "&&" -> Bool (L.fold_left (fldb (&&)) true values)
     | "||" -> Bool (L.fold_left (fldb (||)) false values)
     | "ifthen" ->
       let [tf;ithen;ielse] = values in
       (match tf with
        | Bool true -> eval ithen
        | Bool false -> eval ielse)
     | _   -> failwith "undefined primitive")
  | Fix (x,e) -> eval (substitute x term e)