package incremental

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The stack of bind left-hand sides currently in effect is the current "scope". In order to create a function in one scope and apply it in a different scope, one must manually save and restore the scope. Essentially, the scope should be part of every closure that constructs incrementals. For example:

bind t1 ~f:(fun i1 ->
  let f t2 = map t2 ~f:(fun i2 -> i1 + i2) in
  bind t3 ~f:(fun i -> ... f ...);
  bind t4 ~f:(fun i -> ... f ...));

In the above code, the calls to f will create a map node that unnecessarily depends on the left-hand side of the most recent bind (t3 or t4). To eliminate the unnecessary dependence, one should save and restore the scope for f:

bind t1 ~f:(fun i1 ->
  let scope = Scope.current () in
  let f t2 = Scope.within scope ~f:(fun () -> map t2 ~f:(fun i2 -> i1 + i2)) in
  bind t3 ~f:(fun i -> ... f ...);
  bind t4 ~f:(fun i -> ... f ...))

lazy_from_fun and memoize_fun capture some common situations in which one would otherwise need to use Scope.within.

type t
val top : t

top is the toplevel scope.

val current : unit -> t

current () returns the scope in which a node would be created right now.

val within : t -> f:(unit -> 'a) -> 'a

within t f runs f in scope t, which causes all nodes created by f to be in scope t. An exception raised by f will be raised by within in the usual way.


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