Opt

1 Option

2 Either

Opt

1Option

opt-car

opt-map

2Either

Left

Right

Either

left

right

either

9.0

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Opt🔗 i

Raymond Racine <ray.racine@gmail.com>

1Option🔗 i

(require option )

Utility functions useful for Typed Rackets Option type.

procedure
( opt-carlst)→(Optiona)
lst:(Listofa)

(:opt-car(All(A)((ListofA)->(OptionA))))

Total head function for a hetergeneous list. If the list is non-empty returns the first element else #f.

procedure
( opt-undefined?x)→Boolean
x:(Optiona)

(:opt-defined?(All(a)(Optiona)->Boolean))

Is the option value defined? Of little to no utility, but provided for completeness.

procedure
( opt-exists?xpref)→Boolean
x:(Optiona)
pref:(a->Boolean)

(:opt-exists(All(a)(Optiona)(a->Boolean)->Boolean))

Does the option value exist and does the value match the provided predicate?

procedure
( opt-get-orelsexdef-expr)→a
x:(Optiona)
def-expr:(Thunka)

{ (:opt-get-orelse(All(a)(Optiona)(->a)->a))

Returns the option’s value if defined else the value returned by the provided thunk. }

procedure
( opt-get-orelse-valuexdef-value)→a
x:(Optiona)
def-value:a

(:opt-get-orelse-value(All(a)(Optiona)a->a))

Returns the options’ value if defined else the provided default value.

procedure
( opt-orelsexdef-expr)→(Optiona)
x:(Optiona)
def-expr:(->(Optiona))

{ (:opt-orelse(All(a)(Optiona)(->(Optiona))->(Optiona)))

Returns the provided option itself if its value is defined otherwise the given alternative option. }

procedure
( opt-mapxfn)→(Optionb)
x:(Optiona)
fn:(->ab)

(: opt-map (All (a b) (Option a) (a -> b) -> (Option b)))

Apply the given procedure to the option value if defined.

procedure
( opt-map-orelse-valuexfndefault)→b
x:(Optiona)
fn:(->ab)
default:b

(:opt-map-orelse-value(All(ab)(Optiona)(a->b)b->b))

Apply the given procedure to the option’s value if defined and return it, otherwise return the provided default value.

procedure
( opt-map-orelsexfndefault-expr)→b
x:(Optiona)
fn:(->ab)
default-expr:(Thunkb)

(:opt-map-orelse(All(ab)(Optiona)(a->b)(->b)->b))

Apply the given procedure to the option’s value if defined and return it, otherwise return the value returned from the provided thunk when evaluated.

procedure
( opt-flatmapxfmap)→(Optionb)
x:(Optiona)
fmap:(->a(Optionb))

(:opt-flatmap(All(ab)(Optiona)(a->(Optionb))->(Optionb)))

Use the provided function to translate from an option value of one type to an option value of another type.

procedure
( opt-filterxfn)→(Optiona)
x:(Optiona)
fn:(->aBoolean)

(:opt-filter(All(a)(Optiona)(a->Boolean)->(Optiona)))

If the option is defined and the predicate is satisfied return the option’s value else #f.

procedure
( opt-rejectxfn)→(Optiona)
x:(Optiona)
fn:(->aBoolean)

(:opt-reject(All(a)(Optiona)(a->Boolean)->(Optiona)))

Drop’s the options value (i.e. returns #f) if the value does not match the provided predicate.

procedure
( opt-foreachxproc)→Void
x:(Optiona)
proc:(->aVoid)

(:opt-foreach(All(T)(OptionT)(T->Void)->Void))

Apply a side-effecting procedure to the option’s value if defined, otherwise does nothing. Returns a void value.

2Either🔗 i

(require either )

struct
(struct Left(val)
#:extra-constructor-namemake-Left)
val:E

(struct:(E)Left([val:E])#:transparent)

The left possible value of an Either type. By convention is often the error or failure value or message.

struct
(struct Right(val)
#:extra-constructor-namemake-Right)
val:D

(struct:(D)Right([val:D])#:transparent)

The right possible value of an Either type. By convention is often the correct or success value.

Type
Either:(U(LeftE)(RightD))

(define-type(EitherED)(U(LeftE)(RightD)))

A type whose value is of one type or another. By convention often the Left type value is a failure value value and the Right type value is a success value.

procedure
( leftx)→E
x:(EitherED)

(:left(All(ED)(EitherED)->E))

Project (return) the Either’s value IF it is a Left value, otherwise and error is thrown.

procedure
( rightx)→D
x:(EitherED)

(:right(All(ED)(EitherED)->D))

Project (return the Either’s value IF it is a Right value, otherwise an error is thrown.

procedure
( eitherleft-fnright-fnan-either)→T
left-fn:(->ET)
right-fn:(->DT)
an-either:(EitherED)

(:either(All(EDT)((E->T)(D->T)(EitherED)->T)))

Applies one of the provided procedures to the value of the provided Either argument. Which procedure is applied depends on the type of the provided Either’s value.

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