An educational pure functional programming library in TypeScript
Add data/units module with dimensional types
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src/data/index.ts
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src/data/index.ts
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src/data/units.ts
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src/data/units.ts
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/**
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* Dimensional types for compile-time unit safety.
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*
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* Prevents mixing incompatible units at compile time.
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*
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* @example
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* ```typescript
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* const d = meters(100)
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* const t = seconds(10)
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* const v = velocity(d, t) // Quantity<number, MetersPerSecond>
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*
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* // Type error: can't add meters to seconds
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* // addQ(d, t)
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*
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* // OK: same units
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* const total = addQ(d, meters(50))
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* ```
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*
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* @module data/units
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*/
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// -----------------------------------------------------------------------------
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// Unit Phantom Type
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// -----------------------------------------------------------------------------
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declare const __unit: unique symbol
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type Unit<U> = { [__unit]: U }
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/**
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* Quantity with dimensional unit at type level.
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* Prevents mixing incompatible units (meters + seconds = type error).
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*/
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export type Quantity<T extends number, U> = T & Unit<U>
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// -----------------------------------------------------------------------------
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// Unit Types
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// -----------------------------------------------------------------------------
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export type Meters = "Meters"
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export type Seconds = "Seconds"
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export type Kilograms = "Kilograms"
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export type MetersPerSecond = "MetersPerSecond"
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// -----------------------------------------------------------------------------
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// Constructors
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// -----------------------------------------------------------------------------
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/**
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* Create a quantity in meters.
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*
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* @example
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* ```typescript
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* const distance = meters(100)
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* ```
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*/
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export const meters = (n: number): Quantity<number, Meters> =>
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n as Quantity<number, Meters>
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/**
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* Create a quantity in seconds.
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*
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* @example
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* ```typescript
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* const time = seconds(60)
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* ```
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*/
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export const seconds = (n: number): Quantity<number, Seconds> =>
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n as Quantity<number, Seconds>
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/**
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* Create a quantity in kilograms.
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*
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* @example
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* ```typescript
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* const mass = kilograms(75)
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* ```
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*/
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export const kilograms = (n: number): Quantity<number, Kilograms> =>
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n as Quantity<number, Kilograms>
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// -----------------------------------------------------------------------------
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// Derived Quantities
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// -----------------------------------------------------------------------------
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/**
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* Calculate velocity from distance and time.
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*
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* @example
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* ```typescript
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* const v = velocity(meters(100), seconds(10)) // 10 m/s
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* ```
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*/
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export const velocity = (
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distance: Quantity<number, Meters>,
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time: Quantity<number, Seconds>
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): Quantity<number, MetersPerSecond> =>
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((distance as number) / (time as number)) as Quantity<number, MetersPerSecond>
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// -----------------------------------------------------------------------------
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// Same-Unit Arithmetic
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// -----------------------------------------------------------------------------
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/**
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* Add two quantities of the same unit.
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*
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* @example
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* ```typescript
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* const total = addQ(meters(10), meters(20)) // 30 meters
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* ```
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*/
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export const addQ = <U>(
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a: Quantity<number, U>,
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b: Quantity<number, U>
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): Quantity<number, U> => ((a as number) + (b as number)) as Quantity<number, U>
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/**
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* Subtract two quantities of the same unit.
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*
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* @example
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* ```typescript
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* const diff = subQ(meters(30), meters(10)) // 20 meters
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* ```
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*/
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export const subQ = <U>(
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a: Quantity<number, U>,
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b: Quantity<number, U>
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): Quantity<number, U> => ((a as number) - (b as number)) as Quantity<number, U>
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/**
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* Scale a quantity by a scalar value.
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*
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* @example
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* ```typescript
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* const doubled = scaleQ(2)(meters(50)) // 100 meters
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* ```
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*/
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export const scaleQ =
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(scalar: number) =>
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<U>(q: Quantity<number, U>): Quantity<number, U> =>
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(scalar * (q as number)) as Quantity<number, U>