Module Base.Invariant

This module defines signatures that are to be included in other signatures to ensure a consistent interface to invariant-style functions. There is a signature (S, S1, S2, S3) for each arity of type. Usage looks like:

        type t
        include Invariant.S with type t := t

or

        type 'a t
        include Invariant.S1 with type 'a t := 'a t
type 'a t = 'a Base__.Invariant_intf.t
module type S = Base__.Invariant_intf.S
module type S1 = Base__.Invariant_intf.S1
module type S2 = Base__.Invariant_intf.S2
module type S3 = Base__.Invariant_intf.S3
val invariant : Base__.Source_code_position0.t ‑> 'a ‑> ('a ‑> Sexp.t) ‑> (unit ‑> unit) ‑> unit

invariant here t sexp_of_t f runs f (), and if f raises, wraps the exception in an Error.t that states "invariant failed" and includes both the exception raised by f, as well as sexp_of_t t. Idiomatic usage looks like:

        invariant [%here] t [%sexp_of: t] (fun () ->
          ... check t's invariants ... )

For polymorphic types:

        let invariant check_a t =
          Invariant.invariant [%here] t [%sexp_of: _ t] (fun () -> ... )

It's okay to use [%sexp_of: _ t] because the exceptions raised by check_a will show the parts that are sexp_opaque at top-level.

val check_field : 'a ‑> 'b t ‑> ('a, 'b) Field.t ‑> unit

check_field is used when checking invariants using Fields.iter. It wraps an exception raised when checking a field with the field's name. Idiomatic usage looks like:

        type t =
          { foo : Foo.t;
            bar : Bar.t;
          }
        [@@deriving_inline fields][@@@end]

        let invariant t : unit =
          Invariant.invariant [%here] t [%sexp_of: t] (fun () ->
            let check f = Invariant.check_field t f in
            Fields.iter
              ~foo:(check Foo.invariant)
              ~bar:(check Bar.invariant))
        ;;