tezos-error-monad 10.2 · OCaml Package

Tezos Protocol Implementation - Error Monad

type error_category = [

| `Branch
(*
Errors that may not happen in another context
*)
| `Temporary
(*
Errors that may not happen in a later context
*)
| `Permanent
(*
Errors that will happen no matter the context
*)

]

Categories of error

type error = TzCore.error = ..

include Sig.CORE with type error := error

val error_encoding : error Data_encoding.t

val pp : Format.formatter -> error -> unit

include Sig.EXT with type error := error

val register_error_kind : 
  Sig.error_category ->
  id:string ->
  title:string ->
  description:string ->
  ?pp:(Format.formatter -> 'err -> unit) ->
  'err Data_encoding.t ->
  (error -> 'err option) ->
  ('err -> error) ->
  unit

The error data type is extensible. Each module can register specialized error serializers id unique name of this error. Ex.: overflow_time_counter title more readable name. Ex.: Overflow of time counter description human readable description. Ex.: The time counter overflowed while computing delta increase pp formatter used to pretty print additional arguments. Ex.: The time counter overflowed while computing delta increase. Previous value %d. Delta: %d encoder decoder data encoding for this error. If the error has no value, specify Data_encoding.empty

val register_recursive_error_kind : 
  Sig.error_category ->
  id:string ->
  title:string ->
  description:string ->
  pp:(Format.formatter -> 'err -> unit) ->
  (error Data_encoding.t -> 'err Data_encoding.t) ->
  (error -> 'err option) ->
  ('err -> error) ->
  unit

Same as register_error_kind but allow errors to wrap other errors.

The encoding argument is a function which will be given the encoding of errors as argument so that you can encode errors in errors using a fixpoint.

Another difference with register_error_kind is that pp is mandatory.

val classify_error : error -> Sig.error_category

Classify an error using the registered kinds

type error += private

| Unclassified of string
(*
Catch all error when 'deserializing' an error.
*)

Catch all error when 'serializing' an error.

type error += private

| Unregistered_error of Data_encoding.json

val json_of_error : error -> Data_encoding.json

An error serializer

val error_of_json : Data_encoding.json -> error

Error documentation

type error_info = {

category : Sig.error_category;
id : string;
title : string;
description : string;
schema : Data_encoding.json_schema;

}

Error information

val pp_info : Format.formatter -> error_info -> unit

val find_info_of_error : error -> error_info

find_info_of_error e retrieves the `error_info` associated with the given error `e`.

raises [Invalid_argument]
if the error is a wrapped error from another monad

raises [Not_found]
if the error's constructor has not been registered

val get_registered_errors : unit -> error_info list

Retrieves information of registered errors

include Sig.WITH_WRAPPED with type error := error

module type Wrapped_error_monad = sig ... end

The purpose of this module is to wrap a specific error monad E into a more general error monad Eg.

val register_wrapped_error_kind : 
  (module Wrapped_error_monad) ->
  id:string ->
  title:string ->
  description:string ->
  unit

Same as register_error_kind but for a wrapped error monad. The codec is defined in the module parameter. It makes the category of the error Wrapped instead of Main.

module TzTrace : Sig.TRACE with type 'error trace = 'error list

type 'error trace = 'error TzTrace.trace

include Sig.MONAD with type 'error trace := 'error TzTrace.trace

val ok : 'a -> ('a, 'trace) result

Successful result

val ok_unit : (unit, 'trace) result

val ok_none : ('a option, 'trace) result

val ok_some : 'a -> ('a option, 'trace) result

val ok_nil : ('a list, 'trace) result

val ok_true : (bool, 'trace) result

val ok_false : (bool, 'trace) result

val return : 'a -> ('a, 'trace) result Lwt.t

Successful return

val return_unit : (unit, 'trace) result Lwt.t

Successful return of ()

val return_none : ('a option, 'trace) result Lwt.t

Successful return of None

val return_some : 'a -> ('a option, 'trace) result Lwt.t

return_some x is a successful return of Some x

val return_nil : ('a list, 'trace) result Lwt.t

Successful return of []

val return_true : (bool, 'trace) result Lwt.t

Successful return of true

val return_false : (bool, 'trace) result Lwt.t

Successful return of false

val error : 'err -> ('a, 'err TzTrace.trace) result

Erroneous result

val fail : 'err -> ('a, 'err TzTrace.trace) result Lwt.t

Erroneous return

Infix operators for monadic binds/maps. All operators follow this naming convention:

the first character is >
the second character is > for bind and | for map
the next character is = for Lwt or ? for Error
the next character (if present) is = for Lwt or ? for Error, it is only used for operator that are within both monads.

val (>>=) : 'a Lwt.t -> ('a -> 'b Lwt.t) -> 'b Lwt.t

Lwt's bind reexported. Following Lwt's convention, in this operator and the ones below, = indicate we operate within Lwt.

val (>|=) : 'a Lwt.t -> ('a -> 'b) -> 'b Lwt.t

Lwt's map reexported. The | indicates a map rather than a bind.

val (>>?) : 
  ('a, 'trace) result ->
  ('a -> ('b, 'trace) result) ->
  ('b, 'trace) result

Non-Lwt bind operator. In this operator and the ones below, ? indicates that we operate within the error monad.

val (>|?) : ('a, 'trace) result -> ('a -> 'b) -> ('b, 'trace) result

Non-Lwt map operator.

val (>>=?) : 
  ('a, 'trace) result Lwt.t ->
  ('a -> ('b, 'trace) result Lwt.t) ->
  ('b, 'trace) result Lwt.t

Combined bind operator. The =? indicates that the operator acts within the combined error-lwt monad.

val (>|=?) : 
  ('a, 'trace) result Lwt.t ->
  ('a -> 'b) ->
  ('b, 'trace) result Lwt.t

Combined map operator.

val (>>?=) : 
  ('a, 'trace) result ->
  ('a -> ('b, 'trace) result Lwt.t) ->
  ('b, 'trace) result Lwt.t

Injecting bind operator. This is for transitioning from the simple Error monad to the combined Error-Lwt monad.

Note the order of the character: it starts with the error monad marker ? and has the Lwt monad marker later. This hints at the role of the operator to transition into Lwt.

val (>|?=) : 
  ('a, 'trace) result ->
  ('a -> 'b Lwt.t) ->
  ('b, 'trace) result Lwt.t

Injecting map operator.

val record_trace : 
  'err ->
  ('a, 'err TzTrace.trace) result ->
  ('a, 'err TzTrace.trace) result

Enrich an error report (or do nothing on a successful result) manually

val trace : 
  'err ->
  ('b, 'err TzTrace.trace) result Lwt.t ->
  ('b, 'err TzTrace.trace) result Lwt.t

Automatically enrich error reporting on stack rewind

val record_trace_eval : 
  (unit -> ('err, 'err TzTrace.trace) result) ->
  ('a, 'err TzTrace.trace) result ->
  ('a, 'err TzTrace.trace) result

Same as record_trace, for unevaluated error

val trace_eval : 
  (unit -> ('err, 'err TzTrace.trace) result Lwt.t) ->
  ('b, 'err TzTrace.trace) result Lwt.t ->
  ('b, 'err TzTrace.trace) result Lwt.t

Same as trace, for unevaluated Lwt error

val error_unless : bool -> 'err -> (unit, 'err TzTrace.trace) result

Error on failed assertion

val error_when : bool -> 'err -> (unit, 'err TzTrace.trace) result

val fail_unless : bool -> 'err -> (unit, 'err TzTrace.trace) result Lwt.t

Erroneous return on failed assertion

val fail_when : bool -> 'err -> (unit, 'err TzTrace.trace) result Lwt.t

val unless : 
  bool ->
  (unit -> (unit, 'trace) result Lwt.t) ->
  (unit, 'trace) result Lwt.t

val when_ : 
  bool ->
  (unit -> (unit, 'trace) result Lwt.t) ->
  (unit, 'trace) result Lwt.t

val dont_wait : 
  (exn -> unit) ->
  ('trace -> unit) ->
  (unit -> (unit, 'trace) result Lwt.t) ->
  unit

Wrapper around Lwt_utils.dont_wait

val join_p : unit Lwt.t list -> unit Lwt.t

A few aliases for Lwt functions

val all_p : 'a Lwt.t list -> 'a list Lwt.t

val both_p : 'a Lwt.t -> 'b Lwt.t -> ('a * 'b) Lwt.t

val join_e : 
  (unit, 'err TzTrace.trace) result list ->
  (unit, 'err TzTrace.trace) result

Similar functions in the error monad

val all_e : 
  ('a, 'err TzTrace.trace) result list ->
  ('a list, 'err TzTrace.trace) result

val both_e : 
  ('a, 'err TzTrace.trace) result ->
  ('b, 'err TzTrace.trace) result ->
  ('a * 'b, 'err TzTrace.trace) result

val join_ep : 
  (unit, 'err TzTrace.trace) result Lwt.t list ->
  (unit, 'err TzTrace.trace) result Lwt.t

Similar functions in the combined monad

val all_ep : 
  ('a, 'err TzTrace.trace) result Lwt.t list ->
  ('a list, 'err TzTrace.trace) result Lwt.t

val both_ep : 
  ('a, 'err TzTrace.trace) result Lwt.t ->
  ('b, 'err TzTrace.trace) result Lwt.t ->
  ('a * 'b, 'err TzTrace.trace) result Lwt.t

include Sig.MONAD_EXT
  with type error := error
   and type 'error trace := 'error TzTrace.trace

type tztrace = error TzTrace.trace

type 'a tzresult = ('a, tztrace) result

val classify_errors : tztrace -> Sig.error_category

val pp_print_error : Format.formatter -> error TzTrace.trace -> unit

val pp_print_error_first : Format.formatter -> error TzTrace.trace -> unit

Pretty prints a trace as the message of its first error

val trace_encoding : error TzTrace.trace Data_encoding.t

val result_encoding : 'a Data_encoding.t -> 'a tzresult Data_encoding.t

A serializer for result of a given type

val generic_error : ('a, Format.formatter, unit, 'b tzresult) format4 -> 'a

Erroneous result (shortcut for generic errors)

val failwith : ('a, Format.formatter, unit, 'b tzresult Lwt.t) format4 -> 'a

Erroneous return (shortcut for generic errors)

val error_exn : exn -> 'a tzresult

val error_of_exn : exn -> error trace

error_of_exn e is a trace that carries the exception e. This function is intended to be used when interacting with a part of the code (most likely an external library) which uses exception. E.g.,

try
  Ok (make_some_call parameter)
with
  | (Not_found | Failure _) as e ->
    Error (error_of_exn e)

val record_trace_exn : exn -> 'a tzresult -> 'a tzresult

val trace_exn : exn -> 'b tzresult Lwt.t -> 'b tzresult Lwt.t

val generic_trace : 
  ('a,
    Format.formatter,
    unit,
    ('b, error trace) result Lwt.t ->
    ('b, error trace) result Lwt.t)
    format4 ->
  'a

val pp_exn : Format.formatter -> exn -> unit

val failure : ('a, Format.formatter, unit, error) format4 -> 'a

type error +=

| Exn of exn

Wrapped OCaml/Lwt exception

type error +=

| Canceled

val protect : 
  ?on_error:(error trace -> 'a tzresult Lwt.t) ->
  ?canceler:Lwt_canceler.t ->
  (unit -> 'a tzresult Lwt.t) ->
  'a tzresult Lwt.t

protect is a wrapper around Lwt.catch where the error handler operates over `trace` instead of `exn`. Besides, protect ~on_error ~canceler ~f may *cancel* f via a Lwt_canceler.t.

More precisely, protect ~on_error ~canceler f runs f (). An Lwt failure triggered by f () is wrapped into an Exn. If a canceler is given and Lwt_canceler.cancellation canceler is determined before f (), a Canceled error is returned.

Errors are caught by ~on_error (if given), otherwise the previous value is returned. An Lwt failure triggered by ~on_error is wrapped into an Exn

type error +=

| Timeout

val with_timeout : 
  ?canceler:Lwt_canceler.t ->
  unit Lwt.t ->
  (Lwt_canceler.t -> 'a tzresult Lwt.t) ->
  'a tzresult Lwt.t

package tezos-error-monad

Error documentation