package batteries

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package batteries
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Monadic results of computations that can raise exceptions

type ('a, 'b) t = ('a, 'b) BatPervasives.result =
  1. | Ok of 'a
  2. | Bad of 'b

The type of a result. A result is either Ok x carrying the normal return value x or is Bad e carrying some indication of an error. The value associated with a bad result is usually an exception (exn) that can be raised.

  • since 1.0
val catch : ('a -> 'b) -> 'a -> ('b, exn) t

Execute a function and catch any exception as a result. This function encapsulates code that could throw an exception and returns that exception as a value.

  • since 1.0
val catch2 : ('a -> 'b -> 'c) -> 'a -> 'b -> ('c, exn) t

As catch but two paramaters. This saves a closure construction

  • since 2.0
val catch3 : ('a -> 'b -> 'c -> 'd) -> 'a -> 'b -> 'c -> ('d, exn) t

As catch but three paramaters. This saves a closure construction

  • since 2.0
val get : ('a, exn) t -> 'a

get (Ok x) returns x, and get (Bad e) raises e. This function is, in a way, the opposite of the catch function

  • since 2.0
val default : 'a -> ('a, _) t -> 'a

default d r evaluates to d if r is Bad else x when r is Ok x

  • since 2.0
val map : ('a -> 'b) -> ('a, 'c) t -> ('b, 'c) t

map f (Ok x) returns Ok (f x) and map f (Bad e) returns Bad e.

  • since 2.6.0
val map_both : ('a1 -> 'a2) -> ('b1 -> 'b2) -> ('a1, 'b1) t -> ('a2, 'b2) t

map_both f g (Ok x) returns Ok (f x) and map_both f g (Bad e) returns Bad (g e).

  • since 2.6.0
val map_default : 'b -> ('a -> 'b) -> ('a, _) t -> 'b

map_default d f r evaluates to d if r is Bad else f x when r is Ok x

  • since 2.0
val is_ok : ('a, 'b) t -> bool

is_ok (Ok _) is true, otherwise false.

  • since 2.0
val is_bad : ('a, 'b) t -> bool

is_bad (Bad _) is true, otherwise false

  • since 2.0
val is_exn : exn -> ('a, exn) t -> bool

is_exn e1 r is true iff r is Bad e2 with e1=e2

val of_option : 'a option -> ('a, unit) t

Convert an option to a result

  • since 1.0
val to_option : ('a, _) t -> 'a option

Convert a result to an option

  • since 1.0
The Result Monad

This monad is very similar to the option monad, but instead of being None when an error occurs, the first error in the sequence is preserved as the return value.

module Monad : sig ... end
Infix
module Infix : sig ... end

This infix module provides the operator (>>=)

val print : ('b BatInnerIO.output -> 'a -> unit) -> 'b BatInnerIO.output -> ('a, exn) t -> unit

Print a result as Ok(x) or Bad(exn)