Conditionals

Sometimes, you want to check on something before deciding what to do. BackTalk can help you do this! There is a command called if: that lets you test something, and then run a command if the test passes.

That could look something like this:

if:
    in case (it is raining) then:
        take the umbrella
        put on a jacket

    in case (it is sunny) then:
        put on sunglasses

    otherwise:
        put on layers

In this example, if it's raining, we will take an umbrella, and put on a jacket. If it's sunny, we will put on sunglasses. If it's raining and sunny, then we will take the umbrella and put on a jacket, but won't put on sunglasses. if: only does the first in case $ then: that it can. if: also provides an otherwise: command which will be run only if no cases match. In the example above, we use otherwise: to layer up in unrecognized weather.

You can play with if: in the example below. Try adding an otherwise: in where you can!

-- ConditionalExample

if:
    in case ($bingo is hungry) then:
        feed $bingo

    in case ($harry is hungry) then:
        feed $harry

    in case ($suzy is hungry) then:
        feed $suzy

    otherwise:
        print "no hungry friends!"

if:
    in case ($suzy is bored) then:
        give $suzy a video game

    in case ($harry is bored) then:
        give $harry a book

if: can even be used to calculate a value. We could change the first if: statement in the example above to use with $ as: like so:

-- ConditionalExample

with $hungry_friend as:
    if:
        in case ($bingo is hungry) then:
            $bingo
        in case ($harry is hungry) then:
            $harry
        in case ($suzy is hungry) then:
            $suzy

if:
    in case $hungry_friend then:
        feed $hungry_friend
    otherwise:
        print "no hungry friends!"

Notice that $hungry_friend is set to the result of the if: command, which is determined by which friend is hungry. If no friend is hungry, then $hungry_friend will not refer to anything, meaning the command body of in case $hungry_friend then: will not be run.

You may also have noticed that we are only feeding one of our friends. This works well for the examples, because it lets us explore conditional commands, but it's not very nice. Could you modify the example above to feed each friend, but only when they're hungry?