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structure Array2 : sig
type 'a array2
exception Subscript
val array: (int*int) * '1a -> '1a array2
val sub : 'a array2 * (int*int) -> 'a
val update : 'a array2 * (int*int) * 'a -> unit
val length : 'a array2 -> (int*int)
end = struct
type 'a array2 = {size : (int*int), value : 'a Array.array}
exception Subscript = Subscript
fun index ((i1:int,i2:int),(s1,s2)) =
if i1>=0 andalso i1<s1 andalso i2>=0 andalso i2<s2 then i1*s2+i2
else raise Subscript
fun array(bnds as (i1,i2), v) = {size=bnds, value=Array.array(i1*i2, v)}
fun op sub ({size,value}, indx) = Array.sub(value, index(indx,size))
fun update ({size=size,value=A},i,v) = Array.update(A,index(i,size),v)
fun length{size=size,value=A} = size
end; (* Array2 *)
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