(*
%use "Distributions/implode_shape.fsh" ;;
*)



(* implode_shape : [a] -> [a]

converts multi-dimensional arrays into 1d arrays - 
not to be confused with implode_type : [[a]] -> [a] 

*)

%use "BMF/scan.fsh" ;;

let entry_offset = (scan_back times_int 1) . shape2array
;;


let implode_shape_pr (ys: var b) (xs: var a) =
  new offset =  entry_offset #xs 
  and #k = int_shape in 
  let pr k ndx x = 
    (k := inner_product_int 
		!offset
		!ndx ;
    ys[k] := x)
  in 
    idoall (pr k) xs 
  end 
;;

let implode_shape_sh x = 
  succdim (number_of_entries x) (zerodim (zeroShape x)) 
;;
       
let implode_shape = 
  proc2fun implode_shape_pr implode_shape_sh ;;



(* explode_shape : #[a] -> [a] -> [a] is a partial inverse to
implode_shape. it takes the shape of the result, and some inputs, and
pours them into the desired shape.

*)



let fillup_pr sh y (x:var a) = 
  let pr k (ndxi:var [int]) yi = 
    (k := inner_product_int 
		(entry_offset sh)
		ndxi ;
    yi := x[k])
  in 
  new #k = int_shape in 
    idoall (pr k)  y 
  end
;;


let fillup sh = proc2fun (fillup_pr sh) (fst sh) 
;;

let explode_shape sh x = fillup sh (implode_shape x)
;;

(* Note: this is rather inefficient, due to the presence of an
intermediate data structure. See the incomplete file pour.fsh *)