Version française
Home     About     Download     Resources     Contact us    
Browse thread
Let rec trouble
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: -- (:)
From: Christopher Oliver <oliver@f...>
Subject: Let rec trouble
I'm having trouble with the syntax of let rec.  Consider the following
program for computing Van der Waerden's bound:

  open Num
  open Nat
  open Big_int
  open Ratio

  let rec n k l =
    let rec m i =
      if i =/ Int 0 then
        Int 1 else
        Int 2
          */ (m (pred_num i))
          */ (n (k **/ (m (pred_num i))) (pred_num l)) in
    if l =/ Int 2 then succ_num k else m k;;

  print_string (string_of_num (n (Int 3) (Int 3)));;

I would like to restrict the lexical scope of 'n' by replacing the first
double semicolon with 'in.'  I nest m precisely to capture k and l in m's
lexical environment.  Why is this use forbidden?  I.e. Why shouldn't I be
able to write:

  let rec n k l =
    let rec m i =
      if i =/ Int 0 then
        Int 1 else
        Int 2
          */ (m (pred_num i))
          */ (n (k **/ (m (pred_num i))) (pred_num l)) in
    if l =/ Int 2 then succ_num k else m k
  in
    print_string (string_of_num (n (Int 3) (Int 3)));;

I would prefer not to define a top level symbol, and this seems an
inconsistancy.  Am I missing something?

-- 
Christopher Oliver                     Traverse Internet
Systems Coordinator                    223 Grandview Pkwy, Suite 108
oliver@traverse.net                    Traverse City, Michigan, 49684
let magic f = fun x -> x and more_magic n f = fun x -> f ((n f) x);;