(* 

%use "BMF/scan.fsh" ;;

only for vectors.  *)


let scan_pr f u (y:var b) (x: var a) = 
  (y[0] := u ;
  for 1<= i< lendim #x do
    y[i] := f !y[i-1] !x[i-1]
  done)
;;

let scan f u = proc2fun (scan_pr f u) identity
;;
 

let scan_back_pr f u (y:var b) (x:var a) = 
  let n = lendim #x in 
  y[n-1] := u ;
  for (1<= i< n ) do
    y[n-i-1] := f !y[n-i] !x[n-i]
  done
;;


let scan_back f u = proc2fun (scan_back_pr f u) identity
;; 

(* ----------- *)


let scan_no_unit_pr f (y:var b) (x:var a) = 
  (y[0] := x[0] ;
  for 1<= i< lendim #x do
    y[i] := f !y[i-1] !x[i]
  done)
;;

let scan_no_unit f = proc2fun (scan_no_unit_pr f) identity
;;
 

let scan_back_no_unit_pr f (y:var b) (x:var a) = 
  let n = lendim #x in 
  y[n-1] := x[n-1] ;
  for 1<= i< n  do
    y[n-i-1] := f !y[n-i] !x[n-i-1]
  done
;;


let scan_back_no_unit f = proc2fun (scan_back_no_unit_pr f) identity
;; 


(*

let scantest = scan plus_int 0 (fill {3:int_shape} with [1,2,3]) ;;

let scan_backtest = scan_back plus_int 0 (fill {3:int_shape} with [1,2,3]) ;;

*)