diff --git a/doc/contexts.md b/doc/contexts.md index df0ea4e1d..d4076a7c9 100644 --- a/doc/contexts.md +++ b/doc/contexts.md @@ -1,3 +1,50 @@ -# Context-oriented programming +# Context-oriented mathematics -One of problems \ No newline at end of file +## The problem +A known problem for implementing mathematics in statically-typed languages (and not only in them) is that different +sets of mathematical operation could be defined on the same mathematical objects. Sometimes there is not single way to +treat some operations like basic arithmetic operations on Java/Kotlin `Number`. Sometimes there are different ways to do +the same thing like Euclidean and elliptic geometry vector spaces defined over real vectors. Another problem arises when +one wants to add some kind of behavior to existing entity. In dynamic languages those problems are usually solved +by adding dynamic context-specific behaviors in runtime, but this solution has a lot of drawbacks. + +## Context-oriented approach +One of possible solutions to those problems is to completely separate object numerical representations from behaviors. +In terms of kotlin it means to have separate class to represent some entity without any operations, +for example a complex number: + +```kotlin +data class Complex(val re: Double, val im: Double) +``` +And a separate class or singleton, representing operation on those complex numbers: +```kotlin +object: ComplexOperations{ + operator fun Complex.plus(other: Complex) = Complex(re + other.re, im + other.im) + operator fun Complex.minus(other: Complex) = Complex(re - other.re, im - other.im) +} +``` + +In Java, application of such external operations could be very cumbersome, but Kotlin has a unique feature which allows +to treat this situation: blocks with receivers. So in kotlin, operation on complex number could beimplemented as: +```kotlin +with(ComplexOperations){c1 + c2 - c3} +``` +Kotlin also allows to create functions with receivers: +```kotlin +fun ComplexOperations.doSomethingWithComplex(c1: Complex, c2: Complex, c3: Complex) = c1 + c2 - c3 + +ComplexOperations.doComethingWithComplex(c1,c2,c3) +``` + +In fact, whole parts of proram could run in a mathematical context or even multiple nested contexts. + +In `kmath` contexts are responsible not only for operations, but also for raw object creation and advanced features. + +## Other possibilities + +An obvious candidate to get more or less the same functionality is type-class feature. It allows to bind a behavior to +a specific type without modifying the type itself. On a plus side, type-classes do not require explicit context +declaration, so the code looks cleaner. On the minus side, if there are different sets of behaviors for the same types, +it is impossible to combine them in the single module. Also, unlike type-classes, context could have parameters or even +state. For example in `kmath`, sizes and strides for `NDElement` or `Matrix` could be moved to context to optimize +performance in case of large amount of structures. \ No newline at end of file