73 lines
1.5 KiB
TypeScript
73 lines
1.5 KiB
TypeScript
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/**
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* Index getter
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*/
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export function at<T>(idx: number): (array: ReadonlyArray<T>) => T | undefined {
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if (idx < 0) {
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return (array) => array[array.length + idx];
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} else {
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return (array) => array[idx];
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}
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}
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/**
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* Array first item getter
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*/
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export const first: <T extends ReadonlyArray<any>>(
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array: T,
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) => T[0] | undefined = at(0);
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/**
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* Array second item getter
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*/
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export const second: <T extends ReadonlyArray<any>>(
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array: T,
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) => T[1] | undefined = at(1);
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/**
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* Array third item getter
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*/
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export const third: <T extends ReadonlyArray<any>>(
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array: T,
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) => T[2] | undefined = at(2);
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/**
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* Array last item getter
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*/
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export const last: <T>(array: ReadonlyArray<T>) => T | undefined = at(-1);
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/**
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* Applies map and filter on an array, using a single function
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*/
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export function fmap<A, T extends A>(
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m?: undefined,
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f?: (val: A) => val is T,
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): (array: A[]) => T[];
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export function fmap<A>(
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m?: undefined,
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f?: (val: A) => boolean,
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): (array: A[]) => A[];
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export function fmap<A, B, T extends B>(
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m: (val: A) => B,
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f?: (val: B) => val is T,
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): (array: A[]) => T[];
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export function fmap<A, B>(
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m: (val: A) => B,
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f?: (val: B) => boolean,
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): (array: A[]) => B[];
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export function fmap<A, B>(
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m?: (val: A) => B,
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f?: (val: A | B) => boolean,
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): (array: A[]) => (A | B)[] {
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return (array) => {
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if (m && f) {
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return array.map(m).filter(f);
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} else if (m) {
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return array.map(m);
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} else if (f) {
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return array.filter(f);
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} else {
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return array.slice();
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}
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};
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}
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