Modern compiler implementation in ML - Intro ex. 1

main.ml

type id = string
type binop = Plus | Minus | Times 

type stm = CompoundStm of stm * stm
  | AssignStm of id * exp
  | PrintStm of exp list
  and exp = IdExp of id
  | NumExp of int
  | OpExp of exp * binop * exp
  | EseqExp of stm * exp

let prog = CompoundStm(
  AssignStm("a", OpExp(NumExp(5), Plus, NumExp(3))), 
  CompoundStm(AssignStm(
    "b", 
    EseqExp(PrintStm([IdExp("a"); OpExp(IdExp("a"), Minus, NumExp(1))]), 
    OpExp(NumExp(10), Times, IdExp("a")))), 
    PrintStm([IdExp("b")])))


let maxargs (stm: stm) : int =
  let rec aux (s: stm) : int =
    match s with 
    | CompoundStm(s1, s2) -> max (aux s1) (aux s2)
    | AssignStm(_, e) -> aux_exp e 
    | PrintStm(exps) -> 
      let count = List.length exps in 
      let max_in_reps = List.fold_left (fun acc e -> max acc (aux_exp e)) 0 exps in 
      max count max_in_reps
      and aux_exp (e: exp) : int = 
        match e with 
        | IdExp _ -> 0
        | NumExp _ -> 0
        | OpExp(e1, _, e2) -> max (aux_exp e1) (aux_exp e2)
        | EseqExp(s, e) -> max (aux s) (aux_exp e)
      in 
      aux stm
  let () = Printf.printf "Max args: %d\n" (maxargs prog)