I don't think this is currently possible, so I'd like to suggest a feature to let us initialise variables (local and global) with expressions, instead of "pure" number values. A variable would take the value of the expression when the expression is evaluated when entering the scope of the declaration.
When writing custom behaviours for movement, clipping, etc. I find it easier to use local variables to keep the events readable and maintainable, esp. for temporary values that are used in multiple computations. There are lots of formulas using "sprite size" +/- various offsets +/- arbitrary numbers +/- scaling factors, and it's much quicker to write the expression just once.
At the moment I find myself writing a few :
local number foo = 0
(empty) System > set foo to "exression"[/code:kjk7jnxa]
Which is a bit clunky ; it would be much better to be able to specify the expression directly as the initial value for the scope of the variable. Also, this prevents me from setting the variables as "constant", which again would help with readability and maintainability.
If there's a better way, let me know, otherwise I believe it would be a great addition.
Thanks for reading