How do I write a pure function in EK9 that takes parameters and returns a result?

← Functions and Methods · Ref: Q873

Functions use '->' for input parameters and '<-' for the return value. Mark functions 'as pure' when they have no side effects — pure functions only compute from their inputs.

The return variable is declared on the '<-' line and automatically returned. EK9 has no 'return' statement — the compiler ensures all paths initialise the return variable.

See Q49 for function basics. See Q560 for purity contracts. Use 'ek9 -h function' for syntax.

Example

defines module qa.functions.pure.basics

  defines constant

    ADULT_AGE <- 18

  defines function

    calculateArea() as pure
      ->
        width as Float
        height as Float
      <-
        rtn as Float: width * height

    isAdult() as pure
      -> age as Integer
      <- rtn as Boolean: age >= ADULT_AGE

    formatGreeting() as pure
      -> personName as String
      <- rtn as String: `Hello, ${personName}!`

  defines program

    FunctionDemo()
      stdout <- Stdout()

      area <- calculateArea(5.0, 3.0)
      stdout.println(`Area: ${area}`)

      stdout.println(`Adult: ${isAdult(21)}`)
      stdout.println(formatGreeting("Steve"))

Coming from another language?

Java: methods with return type. Python: def with return. Rust: fn with ->. EK9: '<-' declares return, 'as pure' enforces no side effects.

Keywords: function, output, side-effect, return, input, pure, parameter