new(isNotEmpty) add types for isNotEmpty function, and update isEmpty (…

…#101)

Manually tested against `DefinitelyTyped`, all pass

package.json

@@ -67,9 +67,9 @@
     "dox": "^1.0.0",
     "eslint": "^8.50.0",
     "eslint-plugin-import": "^2.28.1",
-    "ramda": "^0.29.1",
+    "ramda": "^0.30.0",
     "rimraf": "^5.0.5",
-    "tsd": "^0.29.0",
+    "tsd": "^0.31.0",
     "typescript": "^5.2.2",
     "xyz": "^4.0.0"
   }

test/head.test.ts

@@ -1,25 +1,62 @@
 import { expectType } from 'tsd';
 import { head } from '../es';
+import { isNotEmpty } from '../types/isNotEmpty';
 
+// strings always return `string | undefined`, can't determine "emptiness" like you can with arrays
+expectType<string | undefined>(head(''));
 // string always return string
-expectType<string>(head('abc'));
-// emptyString still returns type string. this is due to ramda's implementation `''.chartAt(0) => ''`
-expectType<string>(head(''));
+expectType<string | undefined>(head('abc'));
 
 // array literals will read the type of the first entry
 expectType<string>(head(['fi', 1, 'fum']));
-// but if the array is typed as an `Array<T> or T[]`, then return type will be `T`
-expectType<string | number | undefined>(head(['fi', 1, 'fum'] as Array<string | number>));
-// empty array literals return never
-expectType<never>(head([]));
-// but if it is typed, it will be `T | undefined`
+// empty array literals return undefined
+expectType<undefined>(head([]));
+
+// typed empty array will be `T | undefined`
 expectType<number | undefined>(head([] as number[]));
-// const tuples return the literal type of the first entry
+// as will a typed populated array
+expectType<number | undefined>(head([1, 2, 3] as number[]));
+
+// const tuples return the literal type of the last entry
+expectType<10>(head([10] as const));
 expectType<10>(head([10, 'ten'] as const));
 expectType<'10'>(head(['10', 10] as const));
-// typed tuples return the underlying type
-expectType<number>(head([10, 'ten'] as [number, string]));
-expectType<string>(head(['10', 10] as [string, number]));
+// typed tuples return the type of the last element
+expectType<boolean>(head([true] as [boolean]));
+expectType<number>(head([10, 'ten', true] as [number, string, boolean]));
+expectType<string>(head(['10', 10, false] as [string, number, boolean]));
+// typed empty tuple returns undefined, this is expected because there is no `T` here
+expectType<undefined>(head([] as []));
+
 // typed arrays return `T | undefined`
 expectType<number | string | undefined>(head([10, 'ten'] as Array<number | string>));
 expectType<string | number | undefined>(head(['10', 10] as Array<string | number>));
+expectType<number | string | undefined>(head([10, 'ten'] as ReadonlyArray<number | string>));
+expectType<string | number | undefined>(head(['10', 10] as ReadonlyArray<string | number>));
+
+// cross function testing with isNotEmpty
+// test the type narrowing
+const readonlyArr: readonly number[] = [];
+if (isNotEmpty(readonlyArr)) {
+  expectType<number>(head(readonlyArr));
+}
+
+const readonlyArr2: readonly number[] = [];
+if (!isNotEmpty(readonlyArr2)) {
+  // no-op
+} else {
+  expectType<number>(head(readonlyArr2));
+}
+
+
+const arr: number[] = [];
+if (isNotEmpty(arr)) {
+  expectType<number>(head(arr));
+}
+
+const arr2: number[] = [];
+if (!isNotEmpty(arr2)) {
+  // no-op
+} else {
+  expectType<number>(head(arr2));
+}

test/init.test.ts

@@ -0,0 +1,36 @@
+import { expectType } from 'tsd';
+
+// TODO: check this import to '../es' once this function actually exists in ramda
+import { isNotEmpty } from '../types/isNotEmpty';
+import { init } from '../es';
+
+// string always return string
+expectType<string>(init('abc'));
+// emptyString still returns type string. this is due to `''.chartAt(0) => ''`
+expectType<string>(init(''));
+
+// array literals will read the first type correctly
+expectType<[string, number]>(init(['fi', 1, 'fum']));
+// but if the array is typed as an `Array<T> or T[]`, then return type will be `T`
+expectType<Array<string | number>>(init(['fi', 1, 'fum'] as Array<string | number>));
+// empty array literals return never
+expectType<never[]>(init([]));
+// but if it is typed, it will be `number[]`
+expectType<number[]>(init([] as number[]));
+// single entry tuples return never, since they literally have no init
+expectType<[]>(init([10] as const));
+// tuples return the example type of the input tuple minus the first entry
+expectType<[10, '10']>(init([10, '10', 10] as const));
+expectType<['10', 10]>(init(['10', 10, '10'] as const));
+// typed arrays return the same type
+expectType<Array<number | string>>(init([10, 'ten'] as Array<number | string>));
+expectType<Array<string | number>>(init(['10', 10] as Array<string | number>));
+
+// works correctly with isNotEmpty
+const arr = [1, 2, 3, 4];
+
+expectType<number[]>(init(arr));
+
+if (isNotEmpty(arr)) {
+  expectType<number[]>(init(arr));
+}

test/isNotEmpty.test.ts

@@ -0,0 +1,45 @@
+import { expectType } from 'tsd';
+
+// TODO: check this import to '../es' once this function actually exists in ramda
+import { isNotEmpty } from '../types/isNotEmpty';
+import { ReadonlyNonEmptyArray, NonEmptyArray } from '../es';
+
+
+// test the type narrowing
+const readonlyArr: readonly number[] = [];
+if (isNotEmpty(readonlyArr)) {
+  expectType<ReadonlyNonEmptyArray<number>>(readonlyArr);
+}
+
+const readonlyArr2: readonly number[] = [];
+if (!isNotEmpty(readonlyArr2)) {
+  // no-op
+} else {
+  expectType<ReadonlyNonEmptyArray<number>>(readonlyArr2);
+}
+
+
+const arr: number[] = [];
+if (isNotEmpty(arr)) {
+  expectType<NonEmptyArray<number>>(arr);
+}
+
+const arr2: number[] = [];
+if (!isNotEmpty(arr2)) {
+// no-op
+} else {
+  expectType<NonEmptyArray<number>>(arr2);
+}
+
+
+// tuples retain their type
+const tuple: [number, string] = [1, '1'];
+if (isNotEmpty(tuple)) {
+  expectType<[number, string]>(tuple);
+}
+
+// `as const` retain their type
+const tuple2 = [1, 2, 3] as const;
+if (isNotEmpty(tuple2)) {
+  expectType<readonly [1, 2, 3]>(tuple2);
+}

test/last.test.ts

@@ -0,0 +1,62 @@
+import { expectType } from 'tsd';
+import { last } from '../es';
+import { isNotEmpty } from '../types/isNotEmpty';
+
+// strings always return `string | undefined`, can't determine "emptiness" like you can with arrays
+expectType<string | undefined>(last(''));
+// string always return string
+expectType<string | undefined>(last('abc'));
+
+// array literals will read the type of the first entry
+expectType<string>(last(['fi', 1, 'fum']));
+// empty array literals return undefined
+expectType<undefined>(last([]));
+
+// typed empty array will be `T | undefined`
+expectType<number | undefined>(last([] as number[]));
+// as will a typed populated array
+expectType<number | undefined>(last([1, 2, 3] as number[]));
+
+// const tuples return the literal type of the last entry
+expectType<10>(last([10] as const));
+expectType<'ten'>(last([10, 'ten'] as const));
+expectType<10>(last(['10', 10] as const));
+// typed tuples return the type of the last element
+expectType<boolean>(last([true] as [boolean]));
+expectType<string>(last([true, 10, 'ten'] as [boolean, number, string]));
+expectType<number>(last([false, '10', 10] as [boolean, string, number]));
+// typed empty tuple returns undefined, this is expected because there is no `T` here
+expectType<undefined>(last([] as []));
+
+// typed arrays return `T | undefined`
+expectType<number | string | undefined>(last([10, 'ten'] as Array<number | string>));
+expectType<string | number | undefined>(last(['10', 10] as Array<string | number>));
+expectType<number | string | undefined>(last([10, 'ten'] as ReadonlyArray<number | string>));
+expectType<string | number | undefined>(last(['10', 10] as ReadonlyArray<string | number>));
+
+// cross function testing with isNotEmpty
+// test the type narrowing
+const readonlyArr: readonly number[] = [];
+if (isNotEmpty(readonlyArr)) {
+  expectType<number>(last(readonlyArr));
+}
+
+const readonlyArr2: readonly number[] = [];
+if (!isNotEmpty(readonlyArr2)) {
+  // no-op
+} else {
+  expectType<number>(last(readonlyArr2));
+}
+
+
+const arr: number[] = [];
+if (isNotEmpty(arr)) {
+  expectType<number>(last(arr));
+}
+
+const arr2: number[] = [];
+if (!isNotEmpty(arr2)) {
+  // no-op
+} else {
+  expectType<number>(last(arr2));
+}

test/tail.test.ts

@@ -1,4 +1,7 @@
 import { expectType } from 'tsd';
+
+// TODO: check this import to '../es' once this function actually exists in ramda
+import { isNotEmpty } from '../types/isNotEmpty';
 import { tail } from '../es';
 
 // string always return string
@@ -11,14 +14,23 @@ expectType<[number, string]>(tail(['fi', 1, 'fum']));
 // but if the array is typed as an `Array<T> or T[]`, then return type will be `T`
 expectType<Array<string | number>>(tail(['fi', 1, 'fum'] as Array<string | number>));
 // empty array literals return never
-expectType<never>(tail([]));
+expectType<never[]>(tail([]));
 // but if it is typed, it will be `number[]`
 expectType<number[]>(tail([] as number[]));
 // single entry tuples return never, since they literally have no tail
-expectType<never>(tail([10] as const));
+expectType<[]>(tail([10] as const));
 // tuples return the example type of the input tuple minus the first entry
 expectType<['10', 10]>(tail([10, '10', 10] as const));
 expectType<[10, '10']>(tail(['10', 10, '10'] as const));
 // typed arrays return the same type
 expectType<Array<number | string>>(tail([10, 'ten'] as Array<number | string>));
 expectType<Array<string | number>>(tail(['10', 10] as Array<string | number>));
+
+// works correctly with isNotEmpty
+const arr = [1, 2, 3, 4];
+
+expectType<number[]>(tail(arr));
+
+if (isNotEmpty(arr)) {
+  expectType<number[]>(tail(arr));
+}

types/head.d.ts

@@ -1,9 +1,9 @@
-// string
-export function head(str: string): string;
-// empty tuple - purposefully `never`. `head` should never work on tuple type with no length
-export function head(list: readonly []): never;
-// non-empty tuple
-export function head<T1, TRest>(list: readonly [T1, ...TRest[]]): T1;
-// arrays, because these could be empty, they return `T | undefined`
-// this is no different than the tuple form since `T[]` can be empty at runtime
+import { ReadonlyNonEmptyArray } from '../es';
+
+export function head(str: string): string | undefined;
+// non-empty tuple - Readonly here catches regular tuples too
+export function head<T>(list: readonly [T, ...any[]]): T;
+// non-empty arrays - Readonly here catches regular arrays too
+export function head<T>(list: ReadonlyNonEmptyArray<T>): T;
+// arrays, because these could be empty, they return `T | undefined
 export function head<T>(list: readonly T[]): T | undefined;

types/init.d.ts

@@ -1,2 +1,11 @@
+import { ReadonlyNonEmptyArray, NonEmptyArray } from '../es';
+
+// string
 export function init(list: string): string;
-export function init<T>(list: readonly T[]): T[];
+// `infer Init` only works on types like `readonly [1, '2', 3]` where you will get back `['2', 3]`
+// else, if the type is `string[]`, you'll get back `string[]`
+export function init<T extends readonly [...any]>(list: T):
+T extends readonly [...infer Init, any] ? Init :
+  T extends ReadonlyNonEmptyArray<infer A> ? A[] :
+    T extends NonEmptyArray<infer A> ? A[] : T;
+