Pure Function

Definitions

1. A function that always returns the same output for the same input and has no side effects — it does not modify external state, perform I/O, or depend on anything outside its arguments. Pure functions are trivially testable, cacheable, and parallelizable.

   In plain English: A function that acts like a math formula: same inputs always give the same output, and it does not change anything else in the program.

   Example: "add(2, 3) always returns 5, never writes to a file or checks the clock — that is a pure function."

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