How does EK9 handle return values without a return statement?

Look at this function — notice there is no 'return' keyword anywhere:

  maxOfTwo() as pure
    -> firstNum as Integer, secondNum as Integer
    <- rtn as Integer: firstNum
    if secondNum > firstNum
      rtn: secondNum

The '<- rtn as Integer: firstNum' line DECLARES the return variable and gives it an initial value. The compiler then checks that ALL possible code paths leave 'rtn' with a valid value. If any path could leave it uninitialised, the code won't compile.

This design eliminates an entire category of bugs: forgotten returns, early returns bypassing cleanup, and unreachable code after return. The 'return' keyword simply does not exist in EK9's grammar.

See Q146 for the design rationale. See Q144 for no break/continue/return.

Example

defines module qa.classes.no.return

  defines function

    maxOfTwo() as pure
      ->
        firstNum as Integer
        secondNum as Integer
      <- rtn as Integer: firstNum

      //All paths must set rtn — compiler enforces this
      if secondNum > firstNum
        rtn: secondNum

  defines class

    Formatter
      prefix <- "["
      suffix <- "]"

      default Formatter()

      Formatter()
        ->
          p as String
          s as String
        prefix :=: p
        suffix :=: s

      format()
        -> text as String
        <- rtn as String: `${prefix}${text}${suffix}`

      default operator ?

  defines program

    ReturnDemo()
      stdout <- Stdout()

      bigger <- maxOfTwo(10, 20)
      stdout.println(`Max: ${bigger}`)

      formatter <- Formatter("<", ">")
      if formatter?
        stdout.println(formatter.format("hello"))

Other ways to ask this

Why doesn't EK9 have a return keyword?
How do I return a value from a function in EK9?
What is the '<-' return declaration in EK9?

Coming from another language?

Java: return keyword required. Python: return keyword. Go: return keyword. EK9: '<-' declares return variable, no return statement exists.

Keywords: flow, declaration, return, no-return, variable, arrow, initialise