package async_kernel

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.

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))
;;