Module Belt.Option

Uncurried version of keep

keep optionValue p

If optionValue is Some value and p value = true, it returns Some value; otherwise returns None

keep (Some 10)(fun x -> x > 5);; (* returns [Some 10] *)
keep (Some 4)(fun x -> x > 5);; (* returns [None] *)
keep None (fun x -> x > 5);; (* returns [None] *)

Uncurried version of forEach

forEach optionValue f

If optionValue is Some value, it calls f value; otherwise returns ()

forEach (Some "thing")(fun x -> Js.log x);; (* logs "thing" *)
forEach None (fun x -> Js.log x);; (* returns () *)

getExn optionalValue Returns value if optionalValue is Some value, otherwise raises getExn

getExn (Some 3) = 3;;
getExn None (* Raises getExn error *)

getUnsafe x returns x This is an unsafe operation, it assumes x is neither not None or (Some (None .. ))

Uncurried version of mapWithDefault

mapWithDefault optionValue default f

If optionValue is Some value, returns f value; otherwise returns default

mapWithDefault (Some 3) 0 (fun x -> x + 5) = 8;;
mapWithDefault None 0 (fun x -> x + 5) = 0;;

Uncurried version of map

map optionValue f

If optionValue is Some value, returns Some (f value); otherwise returns None

map (Some 3) (fun x -> x * x) = (Some 9);;
map None (fun x -> x * x) = None;;

Uncurried version of flatMap

flatMap optionValue f

If optionValue is Some value, returns f value; otherwise returns None The function f must have a return type of 'a option

let f (x : float) =
    if x >= 0.0 then
      Some (sqrt x)
    else
      None;;

flatMap (Some 4.0) f = Some 2.0;;
flatMap (Some (-4.0)) f = None;;
flatMap None f = None;;

getWithDefault optionalValue default

If optionalValue is Some value, returns value, otherwise default

getWithDefault (Some 1812) 1066 = 1812;;
getWithDefault None 1066 = 1066;;

orElse optionalValue otherOptional

If optionalValue is Some value, returns Some value, otherwise otherOptional

orElse (Some 1812) (Some 1066) = Some 1812;;
orElse None (Some 1066) = Some 1066;;
orElse None None = None;;

Returns true if the argument is Some value, false otherwise

Returns true if the argument is None, false otherwise

Uncurried version of eq

eq optValue1 optvalue2 predicate

Evaluates two optional values for equality with respect to a predicate function.

If both optValue1 and optValue2 are None, returns true.

If one of the arguments is Some value and the other is None, returns false

If arguments are Some value1 and Some value2, returns the result of predicate value1 value2; the predicate function must return a bool

let clockEqual = (fun a b -> a mod 12 = b mod 12);;
eq (Some 3) (Some 15) clockEqual = true;;
eq (Some 3) None clockEqual = false;;
eq None (Some 3) clockEqual = false;;
eq None None clockEqual = true;;

Uncurried version of cmp

cmp optValue1 optvalue2 comparisonFcn

Compares two optional values with respect to a comparison function

If both optValue1 and optValue2 are None, returns 0.

If the first argument is Some value1 and the second is None, returns 1 (something is greater than nothing)

If the first argument is None and the second is Some value2, returns -1 (nothing is less than something)

If the arguments are Some value1 and Some value2, returns the result of comparisonFcn value1 value2; comparisonFcn takes two arguments and returns -1 if the first argument is less than the second, 0 if the arguments are equal, and 1 if the first argument is greater than the second.

let clockCompare = fun a b -> compare (a mod 12) (b mod 12);;
cmp (Some 3) (Some 15) clockCompare = 0;;
cmp (Some 3) (Some 14) clockCompare = 1;;
cmp (Some 2) (Some 15) clockCompare = -1;;
cmp None (Some 15) clockCompare = -1;;
cmp (Some 14) None clockCompare = 1;;
cmp None None clockCompare = 0;;