Module CCError

module CCError: sig .. end

Error Monad

The variant is polymorphic in the error type
Since 0.5

type 'a sequence = ('a -> unit) -> unit

type 'a equal = 'a -> 'a -> bool

type 'a ord = 'a -> 'a -> int

type 'a printer = Buffer.t -> 'a -> unit

type 'a formatter = Format.formatter -> 'a -> unit

Basics

type ('good, 'bad) t = [ `Error of 'bad | `Ok of 'good ]

val return : 'a -> ('a, 'err) t

Successfully return a value

val fail : 'err -> ('a, 'err) t

Fail with an error

val of_exn : exn -> ('a, string) t

of_exn e uses Printexc to print the exception as a string

val of_exn_trace : exn -> ('a, string) t

of_exn_trace e is similar to of_exn e, but it adds the stacktrace to the error message.

Remember to call Printexc.record_backtrace true and compile with the debug flag for this to work.
Since 0.14

val fail_printf : ('a, Buffer.t, unit, ('a, string) t) Pervasives.format4 -> 'a

fail_printf format uses format to obtain an error message and then returns `Error msg
Since 0.3.3

val map : ('a -> 'b) -> ('a, 'err) t -> ('b, 'err) t

Map on success

val map_err : ('err1 -> 'err2) -> ('a, 'err1) t -> ('a, 'err2) t

Map on error.
Since 0.5

val map2 : ('a -> 'b) ->
       ('err1 -> 'err2) -> ('a, 'err1) t -> ('b, 'err2) t

Same as CCError.map, but also with a function that can transform the error message in case of failure

val iter : ('a -> unit) -> ('a, 'b) t -> unit

Apply the function only in case of `Ok

val get_exn : ('a, 'b) t -> 'a

Extract the value x from `Ok x, fails otherwise. You should be careful with this function, and favor other combinators whenever possible.
Raises Invalid_argument if the value is an error.

val catch : ('a, 'err) t -> ok:('a -> 'b) -> err:('err -> 'b) -> 'b

catch e ~ok ~err calls either ok or err depending on the value of e. This is useful for code that does not want to depend on the exact definition of ('a, 'b) t used, for instance once OCaml gets a standard Result.t type.
Since 0.12

val flat_map : ('a -> ('b, 'err) t) -> ('a, 'err) t -> ('b, 'err) t

val (>|=) : ('a, 'err) t -> ('a -> 'b) -> ('b, 'err) t

val (>>=) : ('a, 'err) t -> ('a -> ('b, 'err) t) -> ('b, 'err) t

val equal : ?err:'err equal ->
       'a equal -> ('a, 'err) t equal

val compare : ?err:'err ord -> 'a ord -> ('a, 'err) t ord

val fold : success:('a -> 'b) -> failure:('err -> 'b) -> ('a, 'err) t -> 'b

fold ~success ~failure e opens e and, if e = `Ok x, returns success x, otherwise e = `Error s and it returns failure s.

Wrappers

The functions CCError.guard, CCError.wrap1, CCError.wrap2 and CCError.wrap3 now return exceptions in case of failure,

val guard : (unit -> 'a) -> ('a, exn) t

guard f runs f () and returns its result wrapped in `Ok. If f () raises some exception e, then it fails with `Error e

val guard_str : (unit -> 'a) -> ('a, string) t

Same as CCError.guard but uses CCError.of_exn to print the exception. See CCError.register_printer

val guard_str_trace : (unit -> 'a) -> ('a, string) t

Same as CCError.guard_str but uses CCError.of_exn_trace instead of CCError.of_exn so that the stack trace is printed.
Since 0.14

val wrap1 : ('a -> 'b) -> 'a -> ('b, exn) t

Same as CCError.guard but gives the function one argument.

val wrap2 : ('a -> 'b -> 'c) -> 'a -> 'b -> ('c, exn) t

Same as CCError.guard but gives the function two arguments.

val wrap3 : ('a -> 'b -> 'c -> 'd) -> 'a -> 'b -> 'c -> ('d, exn) t

Same as CCError.guard but gives the function three arguments.

Applicative

val pure : 'a -> ('a, 'err) t

Synonym of CCError.return

val (<*>) : ('a -> 'b, 'err) t -> ('a, 'err) t -> ('b, 'err) t

a <*> b evaluates a and b, and, in case of success, returns `Ok (a b). Otherwise, it fails, and the error of a is chosen over the error of b if both fail.

val join : (('a, 'err) t, 'err) t -> ('a, 'err) t

join t, in case of success, returns `Ok o from `Ok (`Ok o). Otherwise, it fails with `Error e where e is the unwrapped error of t.
Since 0.15

val both : ('a, 'err) t -> ('b, 'err) t -> ('a * 'b, 'err) t

both a b, in case of success, returns `Ok (o, o') with the ok values of a and b. Otherwise, it fails, and the error of a is chosen over the error of b if both fail.
Since 0.15

Infix

module Infix: sig .. end

Collections

val map_l : ('a -> ('b, 'err) t) -> 'a list -> ('b list, 'err) t

val fold_l : ('b -> 'a -> ('b, 'err) t) -> 'b -> 'a list -> ('b, 'err) t

val fold_seq : ('b -> 'a -> ('b, 'err) t) ->
       'b -> 'a sequence -> ('b, 'err) t

Misc

val choose : ('a, 'err) t list -> ('a, 'err list) t

choose l selects a member of l that is a `Ok _ value, or returns `Error l otherwise, where l is the list of errors.

val retry : int -> (unit -> ('a, 'err) t) -> ('a, 'err list) t

retry n f calls f at most n times, returning the first result of f () that doesn't fail. If f fails n times, retry n f fails with the list of successive errors.

module type MONAD = sig .. end

Monadic Operations

module Traverse (M : MONAD) : sig .. end

Conversions

val to_opt : ('a, 'b) t -> 'a option

val of_opt : 'a option -> ('a, string) t

val to_seq : ('a, 'b) t -> 'a sequence

IO

val pp : 'a printer -> ('a, string) t printer

val pp' : 'a printer ->
       'e printer -> ('a, 'e) t printer

Printer that is generic on the error type
Since 0.19

val print : 'a formatter -> ('a, string) t formatter

val print' : 'a formatter ->
       'e formatter -> ('a, 'e) t formatter

Printer that is generic on the error type
Since 0.19

Global Exception Printers

One can register exception printers here, so they will be used by CCError.guard, CCError.wrap1, etc. The printers should succeed (print) on exceptions they can deal with, and re-raise the exception otherwise. For instance if I register a printer for Not_found, it could look like:

CCError.register_printer

    (fun buf exn -> match exn with

      | Not_found -> Buffer.add_string buf "Not_found"

      | _ -> raise exn

    );;

This way a printer that doesn't know how to deal with an exception will let other printers do it.

val register_printer : exn printer -> unit