Aside from its arguments, a defined command has no access to any variables outside of it. So the following would trigger an error:

$outer = 9

Define Command DoSpecial($arg)

Return $outer + $arg # error, $outer is hidden from our command

End

$result = DoSpecial(11)

You can however declare that an external variable be made visible to the command using the Import Var command:

$outer = 9

Define Command DoSpecial($arg)

Import Var 'outer' # we can now use $outer in our command

Return $outer + $arg

End

$result = DoSpecial(11)

When you import a variable this way, the command has read and write access to the variable, and any changes to the variable are visible to the enclosing scope:

$count = 0

Define Command IncrementCount

Import Var 'count'

$count += 1 # modify the outer $count variable

End

IncrementCount

IncrementCount

Prompt $count # will show 2