An educational pure functional programming library in TypeScript
Add data/guards module with type guards and combinators
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src/data/guards.ts
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src/data/guards.ts
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/**
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* Type guards and combinators for runtime type checking.
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*
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* @module data/guards
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*/
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// =============================================================================
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// Primitive Type Guards
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// =============================================================================
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/** Type guard for string values */
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export const isString = (x: unknown): x is string => typeof x === "string"
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/** Type guard for number values */
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export const isNumber = (x: unknown): x is number => typeof x === "number"
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/** Type guard for boolean values */
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export const isBoolean = (x: unknown): x is boolean => typeof x === "boolean"
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/** Type guard for non-null object values */
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export const isObject = (x: unknown): x is object => typeof x === "object" && x !== null
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/** Type guard for array values */
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export const isArray = (x: unknown): x is unknown[] => Array.isArray(x)
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// =============================================================================
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// Number Property Guards
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// =============================================================================
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/** Type guard for positive numbers (x > 0) */
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export const isPositive = (x: unknown): x is number => isNumber(x) && x > 0
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/** Type guard for negative numbers (x < 0) */
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export const isNegative = (x: unknown): x is number => isNumber(x) && x < 0
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/** Type guard for integer numbers */
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export const isInteger = (x: unknown): x is number => isNumber(x) && Number.isInteger(x)
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/** Type guard for finite numbers (excludes Infinity and NaN) */
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export const isFiniteNumber = (x: unknown): x is number => isNumber(x) && Number.isFinite(x)
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// =============================================================================
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// Guard Combinators
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// =============================================================================
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/** Combines two guards with logical AND - both must pass */
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export const and = <A, B extends A, C extends B>(
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g1: (x: A) => x is B,
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g2: (x: B) => x is C
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) => (x: A): x is C => g1(x) && g2(x)
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/** Combines two guards with logical OR - either must pass */
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export const or = <A, B extends A, C extends A>(
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g1: (x: A) => x is B,
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g2: (x: A) => x is C
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) => (x: A): x is B | C => g1(x) || g2(x)
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/** Negates a guard */
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export const not = <A, B extends A>(
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guard: (x: A) => x is B
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) => (x: A): x is Exclude<A, B> => !guard(x)
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// =============================================================================
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// Property Guards
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// =============================================================================
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/** Creates a guard that checks if an object has a specific property */
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export const hasProperty = <K extends string>(key: K) =>
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<T>(x: T): x is T & Record<K, unknown> =>
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isObject(x) && key in x