package base

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Full standard library replacement for OCaml

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J

Jane Street Group, LLC

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J

Jane Street developers

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base-v0.14.0.tar.gz

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doc/base/Base/Invariant/index.html

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 nonrec 'a t = 'a -> unit

module type S = sig ... end

module type S1 = sig ... end

module type S2 = sig ... end

module type S3 = sig ... end

val invariant : 
  Caml.Lexing.position ->
  '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 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 fields]

  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))
  ;;