nullable-quantifier
v0.1.2
Published
Quantifiers of nullable types like as Array.prototype every/some
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Nullable Quantifier
Existential quantifier and Universal quantifier of nullable types (like as some/every of Array.prototype)
Installation
npm install nullable-quantifier
Usage
import { some, every } from 'nullable-quantifier';
const nullableValue1: string | null | undefined = 'Hello World';
const nullableValue2: string | null | undefined = null;
some(nullableValue1, (s) => s.startsWith('Hello')); // true
some(nullableValue2, (s) => s.startsWith('Hello')); // false
every(nullableValue1, (s) => s.includes('foo')); // false
every(nullableValue2, (s) => s.includes('foo')); // true
The some
function accepts a nullable value and a predicate.
If the value is null
or undefined
, some
returns false always,
otherwise some
tests whether passes the provided predicate. (like as Array.prototype.some)
The every
function accepts a nullable value and a predicate.
If the value is null
or undefined
, every
returns true always,
otherwise every
tests whether passes the provided predicate. (like as Array.prototype.every)
Signature
const some = <A>(a: A | null | undefined, p: (_: A) => boolean): boolean
const every = <A>(a: A | null | undefined, p: (_: A) => boolean): boolean
Usecase1. validate optional values
import { every } from 'nullable-quantifier';
type UserForm = {
name: string;
nickname?: string;
}
function validateUserForm(form: UserForm): boolean {
// Check that `name` is always non-empty.
// Check that `nickname` is not empty if and only if it is specified.
return nonEmpty(form.name) && every(form.nickname, nonEmpty);
}
const nonEmpty = (s: string): boolean => s.length > 0;
Alias
The aliases exists
for some
and forall
for every
are defined.
import { exists, forall } from 'nullable-quantifier';
const nullableValue1: string | null | undefined = 'Hello World';
const nullableValue2: string | null | undefined = null;
exists(nullableValue1, (s) => s.startsWith('Hello')); // true
exists(nullableValue2, (s) => s.startsWith('Hello')); // false
forall(nullableValue1, (s) => s.includes('foo')); // false
forall(nullableValue2, (s) => s.includes('foo')); // true