An educational pure functional programming library in TypeScript
Add prelude/option module with Option type and operations
+39
+1
src/prelude/index.ts
+1
src/prelude/index.ts
+38
src/prelude/option.ts
+38
src/prelude/option.ts
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// Types
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export type Some<T> = { readonly _tag: "Some"; readonly value: T }
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export type None = { readonly _tag: "None" }
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export type Option<T> = Some<T> | None
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// Constructors
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export const some = <T>(value: T): Some<T> => ({ _tag: "Some", value })
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export const none: None = { _tag: "None" }
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// Type guards
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export const isSome = <T>(o: Option<T>): o is Some<T> => o._tag === "Some"
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export const isNone = <T>(o: Option<T>): o is None => o._tag === "None"
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// From nullable
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export const fromNullable = <T>(value: T | null | undefined): Option<T> =>
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value == null ? none : some(value)
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// Operations - expression only
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export const mapOption = <T, U>(f: (t: T) => U) =>
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(option: Option<T>): Option<U> =>
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option._tag === "Some" ? some(f(option.value)) : none
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export const flatMapOption = <T, U>(f: (t: T) => Option<U>) =>
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(option: Option<T>): Option<U> =>
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option._tag === "Some" ? f(option.value) : none
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export const getOrElse = <T>(defaultValue: T) =>
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(option: Option<T>): T =>
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option._tag === "Some" ? option.value : defaultValue
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export const matchOption = <T, R>(
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onSome: (value: T) => R,
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onNone: () => R
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) => (option: Option<T>): R =>
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option._tag === "Some" ? onSome(option.value) : onNone()
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export const toNullable = <T>(option: Option<T>): T | null =>
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option._tag === "Some" ? option.value : null