Evaluating expressions within function arguments

So this is hopefully a really stupid and easy-to-answer question.

I am upgrading a twine game from 1.4 to 2 in Sugarcube.

Previously, I was able to use stuff like:

<<set $foo = 25 + Math.floor( $bar / 2 ) >>

But now I cannot put an expression like "$bar / 2" into a function call, apparently?

Can I surround the expression with some character or something that will allow it to be evaluated and then passed to the function?

Thanks much!