Module Bonsai.Dynamic_scope

This module implements dynamic variable scoping. Once a dynamic variable is created, you can store values in it, and lookup those same values. A lookup will find the nearest-most parent "unreverted" set call where a "set" can be "reverted" with set''s revert.

type 'a t = 'a Cont.Dynamic_scope.t
val create : ?sexp_of:('a -> Core.Sexp.t) -> name:string -> fallback:'a -> unit -> 'a t

Creates a new variable for use with the rest of the functions. It is critically important that the exact same Dynamic_scope.t is used in calls to set and the corresponding lookup.

val derived : ?sexp_of:('a -> Core.Sexp.t) -> 'b t -> get:('b -> 'a) -> set:('b -> 'a -> 'b) -> 'a t

Creates a variable which is derived from another. Typically this is used to project out a field of another dynamic variable which contains a record.

val set : here:lexing_position -> 'a t -> 'a Value.t -> inside:'r Computation.t -> 'r Computation.t

Given a 'a Dynamic_scope.t and a 'a Value.t evaluate a function whose resulting Computation.t has access to the value via the lookup function.

type revert = {
  1. revert : 'a. 'a Computation.t -> 'a Computation.t;
}
val set' : here:lexing_position -> 'a t -> 'a Value.t -> f:(revert -> 'r Computation.t) -> 'r Computation.t

like set but with the ability to revert the value in sub-computations.

val lookup : here:lexing_position -> 'a t -> 'a Computation.t

Lookup attempts to find the value inside the nearest scope, but if there isn't one, it falls back to default specified in create.

val modify : here:lexing_position -> 'a t -> change:('a Value.t -> 'a Value.t) -> f:(revert -> 'r Computation.t) -> 'r Computation.t