b0 0.0.0 · OCaml Package

Result values (as in 4.08)

Except for the function of this section that's the Result module that went into 4.08.

Results

type ('a, 'e) t = ('a, 'e) result =

| Ok of 'a
| Error of 'e

The type for result values. Either a value Ok v or an error Error e.

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

ok v is Ok v.

val error : 'e -> ('a, 'e) result

error e is Error e.

val value : ('a, 'e) result -> default:'a -> 'a

value r ~default is v if r is Ok v and default otherwise.

val get_ok : ('a, 'e) result -> 'a

get_ok r is v if r is Ok v and

raises Invalid_argument
otherwise.

val get_error : ('a, 'e) result -> 'e

get_error r is e if r is Error e and

raises Invalid_argument
otherwise.

val bind : ('a, 'e) result -> ('a -> ('b, 'e) result) -> ('b, 'e) result

bind r f is Ok (f v) if r is Ok v and r if r is Error _.

val join : (('a, 'e) result, 'e) result -> ('a, 'e) result

join rr is r if rr is Ok r and rr if rr is Error _.

val map : ('a -> 'b) -> ('a, 'e) result -> ('b, 'e) result

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) result -> ('a, 'f) result

map_error f r is Error (f e) if r is Error e and r if r is Ok _.

val fold : ok:('a -> 'c) -> error:('e -> 'c) -> ('a, 'e) result -> '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) result -> unit

iter f r is f v if r is Ok v and () otherwise.

val iter_error : ('e -> unit) -> ('a, 'e) result -> unit

iter_error f r is f e if r is Error e and () otherwise.

Predicates and comparisons

val is_ok : ('a, 'e) result -> bool

is_ok r is true iff r is Ok _.

val is_error : ('a, 'e) result -> bool

is_error r is true iff r is Error _.

val equal : 
  ok:('a -> 'a -> bool) ->
  error:('e -> 'e -> bool) ->
  ('a, 'e) result ->
  ('a, 'e) result ->
  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) result ->
  ('a, 'e) result ->
  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.

Interacting with `Stdlib` exceptions

val to_failure : ('a, string) result -> 'a

to_failure r is failwith e if r is Error e and v if r is Ok v.

val catch_failure : (unit -> 'a) -> ('a, string) result

catch_failure f is try Ok (f ()) with Failure e -> Error e

val catch_sys_error : (unit -> 'a) -> ('a, string) result

catch_sys_error f is try Ok (f ()) with Sys_error e -> Error e

Converting

val to_option : ('a, 'e) result -> 'a option

to_option r is r as an option, mapping Ok v to Some v and Error _ to None.

val to_list : ('a, 'e) result -> 'a list

to_list r is [v] if r is Ok v and [] otherwise.

package b0

Results

Predicates and comparisons

Interacting with Stdlib exceptions

Converting

Interacting with `Stdlib` exceptions