function programming approach for error and null handling

API Reference

Maybe<A>

• just :: <A>(value: A) => Maybe<A>

  create a Just object

• nothing :: <A>() => Maybe<A>

  create a Nothing object

• fromObject :: <A>(obj: NothingObject | JustObject<A>) => Result<Maybe<A>, string>

  convert a JustObject<A> or NothingObject to a Maybe<A>

• fromString :: <A>(s: string) => Result<Maybe<A>, string>

  convert a string generated by stringify the Maybe<A> to a Maybe<A>

• fromNullable :: <A>(value: A | null | undefined) => Maybe<A>

  Creates a Maybe instance from a nullable value.

• isMaybe :: <T>(v: unknown) => v is Maybe<T>

  type predicate function, test if a varibale is Maybe Object

Maybe instance

• isJust / isNothing :: () => boolean

  indicate the instance is Just<A> / Nothing<A>

• unwrap :: () => A

  returns the contained Maybe value, would panic on Nothing

• unwrapOr :: (defaultValue: A) => A

  returns the contained Maybe value or a provided default value(if Nothing).

• unwrapOrElse: (f: () => A) => A

  returns the contained Maybe value or return the parameter function's return value(if Nothing).

• map :: <B>(f: (v: A) => B) => Maybe<B>

  convert Maybe<A> to Maybe<B> without unwrap the Maybe type which may caust an error

• mapOr :: <B>(f: (v: A) => B, defaultValue: B) => B

  returns the provided default result (if Nothing), or applies the function to the contained value (if Just).

• mapOrElse :: <B>(f: (v: A) => B, defaultValue: () => B) => B

  computes a default function result (if Nothing), or applies a different function to the contained value (if Just).

• toResult: <B>(err: B) => Result<A, B>

  transforms the Maybe<A> into a Result<A, B>, mapping Just<A> to Ok<A> and Nothing to Err<B>.

• ap :: <B>(other: Maybe<A>) => Maybe<B>

  apply a Maybe<(a: A) => B> to a Maybe<A>,

  note that the caller instance should be Maybe<(a: A) => B>.

• bind :: <B>(f: (a: A) => Maybe<B>) => Maybe<B>

  apply a function to the Maybe value without concerning about Nothing.

  return Nothing if Nothing.

• match :: <B>(onJust: (a: A) => B, onNothing: () => B) => B

do something on Maybe<A>, note that you should handle the two cases: Just<A> and Nothing

if return some value, the two handlers should return the same type.

if you want to return different types, use do instead.

• do :: <T, U>(onJust: (a: A) => T, onNothing: () => U) => T | U

do something on Maybe<A>, note that you should handle the two cases: Just<A> and Nothing

Result<A, B>

• ok :: <A, B>(value: A) => Result<A, B>

  create a Ok<A> from value

• err :: <A, B>(msg: B) => Result<A, B>

  create a Err<B> from value

• fromString :: <A, B>(s: string) => Result<Result<A, B>, string>

  convert a string generated by stringify the Result<A, B> to a Result<A, B>

• fromObject :: <A, B>(obj: OkObject<A> | ErrObject<B>) => Result<Result<A, B>, string>

  convert a OkObject<A> or a ErrObject<B> to Result<A, B>

• fromPromise :: <A, B = unknown>(promise: Promise<A>) => Promise<Result<A, B>>

  convert a Promise<A> to a Promise<Result<A, B>>, handle the error by to function

• isResult :: <A, B>(v: unknown) => v is Result<A, B>

  type predicate function, test if a varibale is Result Object

Result instance

• isOk / isErr :: () => boolean

  indicate the instance is Ok<A> / Err<B>

• unwrap :: () => A

  returns the contained Ok value, panic on Err.

• unwrapErr :: () => B

  returns the contained Err value, panic on Ok.

• unwrapOr :: (defaultValue: A) => A

  returns the contained Ok value or a provided default(if Err).

• unwrapOrElse :: (f: () => A) => A

  returns the contained Ok value or computes it from the function(if Err).

• map: <A1>(f: (v: A) => A1)=> Result<A1, B>

  maps a Result<A, B> to Result<A1, B> by applying a function to a contained Ok value, leaving an Err value untouched.

• mapErr :: <B1>(f: (v: B) => B1) => Result<A, B1>

  maps a Result<A, B> to Result<A, B1> by applying a function to a contained Err value, leaving an Ok value untouched.

• mapOr: <A1>(f: (v: A) => A1, defaultValue: A1) => A1

  returns the provided default (if Err), or applies a function to the contained value (if Ok) and return it.

• mapOrElse: <A1>(f: (v: A) => A1, defaultValue: () => A1) => A1

  maps a Result<A, B> to A1 by applying fallback function default to a contained Err value,

  or function f to a contained Ok value.

• ap :: <A1, A2>(other: Result<A1, B>) => Result<A2, B>

  apply a Result<(a: A1) => A2, B> to a Result<A1, B>,

  note that the caller instance should be Result<(a: A) => A1, B>.

• bind :: <A1>(f: (a: A) => Result<A1, B>) =>Result<A1, B>

  apply a function to the Ok value without concerning about Err.

  return Err if Err.

• match :: <T>(f: (v: A) => T, g: (v: B) => T) => T

do something on Result<A, B>, note that you should handle the two cases: Ok<A, B> and Err<A, B>

if return some value, the two handlers should return the same type.

if you want to return different types, use do instead.

• do :: <T, U>(f: (v: A) => T, g: (v: B) => U) => T | U

do something on Result<A, B>, note that you should handle the two cases: Ok<A, B> and Err<A, B>