Allbugs {
    define moveAndTurn using amt {
        move amt
        angle = angle + 90
        exit if x < 0
        exit if x > 100
    }
}
Bug Sally {
    var delta, amount    
    initially {
        color red
        x = 50
        y = 50
        amount = 1
        delta = 1
        angle = 0
    }
    turn 0 // wait two beats
    turn 0
    loop {
        do moveAndTurn(amount)
        amount = amount + delta
    }
}
Bug Fred {
    var delta, amount
    initially {
    color blue
        x = 50
        y = 49
        amount = 1
        delta = 1
        angle = 180
    }
    loop {
        do moveAndTurn(amount)
        amount = amount + delta
    }
}