module BatResult:sig
..end
Monadic results of computations that can raise exceptions
type('a, 'e)
t =('a, 'e) BatPervasives.result
=
| |
Ok of |
| |
Error of |
The type of a result. A result is either Ok x
carrying the
normal return value x
or is Error e
carrying some indication of an
error. The value associated with a bad result is usually an exception
(exn
) that can be raised.
val ok : 'a -> ('a, 'b) t
ok v
is Ok v
.
val error : 'e -> ('a, 'e) t
error e
is Error e
.
val value : ('a, 'e) t -> default:'a -> 'a
value r ~default
is v
if r
is Ok v
and default
otherwise.
val default : 'a -> ('a, 'b) t -> 'a
default d r
evaluates to d
if r
is Error
else x
when r
is
Ok x
.
value
or a slightly different signature.val get_ok : ('a, 'e) t -> 'a
get_ok r
is v
if r
is Ok v
and
Invalid_argument
otherwise.val get_error : ('a, 'e) t -> 'e
get_error r
is e
if r
is Error e
and
Invalid_argument
otherwise.val get : ('a, exn) t -> 'a
get (Ok x)
returns x
, and get (Error e)
raises e
. This
function is, in a way, the opposite of the catch
function
val catch : ('a -> 'e) -> 'a -> ('e, 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.
val catch2 : ('a -> 'b -> 'c) -> 'a -> 'b -> ('c, exn) t
As catch
but two parameters. This saves a closure construction
val catch3 : ('a -> 'b -> 'c -> 'd) -> 'a -> 'b -> 'c -> ('d, exn) t
As catch
but three parameters. This saves a closure construction
val bind : ('a, 'e) t -> ('a -> ('b, 'e) t) -> ('b, 'e) t
bind r f
is f v
if r
is Ok v
and r
if r
is Error _
.
val join : (('a, 'e) t, 'e) t -> ('a, 'e) t
join rr
is r
if rr
is Ok r
and rr
if rr
is Error _
.
val map : ('a -> 'b) -> ('a, 'e) t -> ('b, 'e) t
map f r
is Ok (f v)
if r
is Ok v
and r
if r
is Error _
.
val map_error : ('e -> 'f) -> ('a, 'e) t -> ('a, 'f) t
map_error f r
is Error (f e)
if r
is Error e
and r
if
r
is Ok _
.
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 (Error e)
returns Error (g e)
.
val map_default : 'b -> ('a -> 'b) -> ('a, 'c) t -> 'b
map_default d f r
evaluates to d
if r
is Error
else f x
when r
is Ok x
val fold : ok:('a -> 'c) -> error:('e -> 'c) -> ('a, 'e) t -> 'c
fold ~ok ~error r
is ok v
if r
is Ok v
and error e
if r
is Error e
.
val iter : ('a -> unit) -> ('a, 'e) t -> unit
iter f r
is f v
if r
is Ok v
and ()
otherwise.
val iter_error : ('e -> unit) -> ('a, 'e) t -> unit
iter_error f r
is f e
if r
is Error e
and ()
otherwise.
val is_ok : ('a, 'e) t -> bool
is_ok (Ok _)
is true
, otherwise false
.
val is_error : ('a, 'e) t -> bool
is_error r
is true
iff r
is Error _
.
val is_bad : ('a, 'e) t -> bool
Same as is_error
.
val is_exn : exn -> ('a, exn) t -> bool
is_exn e1 r
is true
iff r
is Error e2
with e1=e2
val equal : ok:('a -> 'a -> bool) ->
error:('e -> 'e -> bool) ->
('a, 'e) t -> ('a, 'e) t -> bool
equal ~ok ~error r0 r1
tests equality of r0
and r1
using ok
and error
to respectively compare values wrapped by Ok _
and
Error _
.
val compare : ok:('a -> 'a -> int) ->
error:('e -> 'e -> int) ->
('a, 'e) t -> ('a, 'e) t -> int
compare ~ok ~error r0 r1
totally orders r0
and r1
using ok
and
error
to respectively compare values wrapped by Ok _
and Error _
.
Ok _
values are smaller than Error _
values.
val to_option : ('a, 'b) t -> 'a option
to_option r
is r
as an option, mapping Ok v
to Some v
and
Error _
to None
.
val of_option : 'a option -> ('a, unit) t
Convert an option
to a result
val to_list : ('a, 'e) t -> 'a list
to_list r
is [v]
if r
is Ok v
and []
otherwise.
val to_seq : ('a, 'e) t -> 'a BatSeq.t
to_seq r
is r
as a sequence. Ok v
is the singleton sequence
containing v
and Error _
is the empty sequence.
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
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 Error(exn)