package batteries

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package batteries
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Operations on references.

References are mutable values, i.e. "variables" which may actually change value during their life-time, as variables in imperative languages. References can be understood as 1-cell arrays and are typically used to implement imperative algorithms in OCaml.

References are useful but don't abuse them.

  • author Xavier Leroy (base module)
  • author David Teller
type 'a t = 'a Pervasives.ref

The type of references.

val ref : 'a -> 'a Pervasives.ref

Return a fresh reference containing the given value.

val (!) : 'a Pervasives.ref -> 'a

!r returns the current contents of reference r. Equivalent to fun r -> r.contents.

val (:=) : 'a Pervasives.ref -> 'a -> unit

r := a stores the value of a in reference r. Equivalent to fun r v -> r.contents <- v.

val set : 'a Pervasives.ref -> 'a -> unit

As :=

val get : 'a Pervasives.ref -> 'a

As !

val copy : 'a Pervasives.ref -> 'a Pervasives.ref

copy r returns a new reference with the same initial content as r.

val pre : 'a Pervasives.ref -> ('a -> 'a) -> 'a

Perform an operation on a reference and return the new value of that reference.

For instance, if x is a reference to 1, pre x ( ( + ) 1) returns 2 and sets x to 2.

val post : 'a Pervasives.ref -> ('a -> 'a) -> 'a

Perform an operation on a reference and return the previous value of that reference.

For instance, if x is a reference to 1, post x ( ( + ) 1) returns 1 and sets x to 2.

val swap : 'a Pervasives.ref -> 'a Pervasives.ref -> unit

swap a b puts !b in a and !a in b

val post_incr : int Pervasives.ref -> int

Increment an integer, return the old value.

Comparable to C or Java's i++.

val post_decr : int Pervasives.ref -> int

Decrement an integer, return the old value.

Comparable to C or Java 's i--.

val pre_incr : int Pervasives.ref -> int

Increment an integer, return the new value.

Comparable to C or Java's ++i.

val pre_decr : int Pervasives.ref -> int

Increment an integer, return the new value.

Comparable to C or Java's --i.

val protect : 'a Pervasives.ref -> 'a -> (unit -> 'b) -> 'b

Assign a reference temporarily.

protect r v body sets the value of r to v and executes body. Once body has been executed, whether termination happens as a consequence of regular evaluation or exception, the previous value of r is restored.

val toggle : bool Pervasives.ref -> unit

Invert the boolean stored in the reference

val oset : 'a option Pervasives.ref -> 'a -> unit

Set the given option ref to Some x

val oget_exn : 'a option Pervasives.ref -> 'a

Get a value from an option ref;

  • raises Not_found

    on oget_exn (ref None)

Boilerplate code
val print : ('b BatInnerIO.output -> 'a -> unit) -> 'b BatInnerIO.output -> 'a t -> unit

Given a printing function for the value in the ref, produce a printing function for the ref.

Example: IO.to_string (Ref.print Int.print) (ref 20) = "20"

val compare : 'a BatOrd.comp -> 'a Pervasives.ref BatOrd.comp

Given a comparison function, produce a comparison function for refs of that type.

Example: let a = ref 10 and b = ref 20 in Ref.compare Int.compare a b = -1

Given an ordering function, produce an ordering function for refs of that type.

Example: let a = ref 10 and b = ref 20 in Ref.ord Int.ord a b = Ord.Lt