root/cobra/trunk/HowTo/130-MakeABranchStatement.cobra

"""
MakeABranchStatement.cobra

General syntax:

    branch WHAT
        on VALUE1
            STATEMENTS1
        on VALUE2
            STATEMENTS2
        [else
            STATEMENTS]

    branch WHAT
        on VALUE1, STATEMENT1
        on VALUE2, STATEMENT2
        [else, STATEMENT]

Key rules of the branch statement:

    * What's being branched on must be an integer, character, enumeration or string.

    * The expressions being matched must be constants (ex: 0, 1, 'x', State.Off, "foo").

When a branch statement isn't feasible, you can possibly:

    * Make a class hierarchy and send a message to the object.

    * Use an `if-else` ladder (see MakeAnIfElseLadder.cobra)


See also: MakeAnIfElseLadder.cobra, CheckInheritanceAndImplementation.cobra.
"""


class Program

    def main

        word = ''

        # This is the general syntax, below. Notice the keywords `branch` and
        # `on` as well as the indentation under each `on` part:
        x = 2
        branch x
            on 1
                isEven = false
                word = 'one'
            on 2
                isEven = true
                word = 'two'
            on 3
                isEven = false
                word = 'three'
        assert isEven
        assert word == 'two'

        # In addition to `on`, you can put an `else` at the end:
        x = 2
        branch x
            on 1
                word = 'one'
            on 3
                word = 'three'
            else
                word = 'else'
        assert word == 'else'

        # If there is only one statement for the `on` or `else` and you want to
        # tighten up your code, you can do so by using a colon (,) and putting the
        # statement on the same line, like so:
        x = 2
        branch x
            on 1, word = 'one'
            on 3, word = 'three'
            else, word = 'else'
        assert word == 'else'

        # You can have more than one value for `on`:
        x = 2
        branch x
            on 1 or 2 or 3, word = 'number'
            else, word = 'else'
        assert word == 'number'

        # You can also branch on enumerations, strings and characters.