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map.ts
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map.ts
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/**
* Converts a function from `X` to `Y` to a function from `Promise<X>` to `Promise<Y>`.
*
* @param f is a function.
* @returns a fully asynchronous version of the input function.
*/
export function map<X, Y>(
f: (x: X) => Y,
): (x: Promise<X>) => Promise<Y> {
return async (x) => f(await x);
}
/**
* Converts a function from `X` to `Promise<Y>` to a function from `Promise<X>` to `Promise<Y>`.
*
* @param f is an asynchronous function.
* @returns a fully asynchronous version of the input function.
*/
export function mapAsync<X, Y>(
f: (x: X) => Promise<Y>,
): (x: Promise<X>) => Promise<Y> {
return async (x) => f(await x);
}
/**
* Combines two functions using classic function composition.
*
* @param f is the first function.
* @param g is the second function.
* @returns a function that is composed of the input functions.
*/
export function pipe<X, Y, Z>(
f: (x: X) => Y,
g: (y: Y) => Z,
): (x: X) => Z {
return (x) => g(f(x));
}
/**
* Converts a promise to a boolean representation of its resolution status.
*
* @param p is any promise.
* @returns a promise that resolves to true if the input promise resolves, otherwise false.
*/
export async function getSuccess(p: Promise<unknown>) {
try {
await p;
return true;
} catch (_) {
return false;
}
}
/**
* Async function that converts an async buffer to a string.
*/
export const getText = map(toText);
function toText(buf: Uint8Array): string {
return new TextDecoder().decode(buf);
}
/**
* Async function that converts an async buffer to an array of lines.
*/
export const getLines = map(toLines);
function toLines(buf: Uint8Array): string[] {
return (toText(buf)).split("\n");
}
/**
* Async function that converts an async buffer to an array of non-empty lines.
*/
export const getLinesNonEmpty = map(toNonEmptyLines);
function toNonEmptyLines(buf: Uint8Array): string[] {
return (toLines(buf)).filter(Boolean);
}
/**
* Async function that returns the first element of an async array, or fails if the array is empty.
*/
export const getFirst = map(toFirst);
function toFirst<T>(array: T[]): T {
if (!array.length) {
throw new Error(
`The first item cannot be retrieved since the array is empty.`,
);
}
return array[0];
}