References

A mutable variable, or "reference" in ML terminology, is simply a record with a single mutable field contents.

Generic references

Creation, access, and assignment are provided as ref, prefix !, and infix :=, respectively.

module Ref

  use export why3.Ref.Ref

  let function (!) (r: ref 'a) = r.contents

  let (:=) (ref r:'a) (v:'a) ensures { r = v } = r <- v

end

Integer References

A few operations specific to integer references.

module Refint

  use int.Int
  use export Ref

  let incr (ref r: int) ensures { r = old r + 1 } = r <- r + 1
  let decr (ref r: int) ensures { r = old r - 1 } = r <- r - 1

  let (+=)   (ref r: int) (v: int) ensures { r = old r + v } = r <- r + v
  let (-=)   (ref r: int) (v: int) ensures { r = old r - v } = r <- r - v
  let ( *= ) (ref r: int) (v: int) ensures { r = old r * v } = r <- r * v

end