Wow, thanks for all the feedback! I agree that expression level editing can get pretty cumbersome at times, it's the biggest design challenge in the editor I think. One thing we may add is a toggle to edit expressions in plain text and parse them back into the visual bubbles.

Re: the fact that syntax errors are possible: it is really really hard to make an editor where invalid states are impossible while trying to make expressions easy to enter. Scratch and other block languages do this by forcing you to write code in prefix order. I want to PLUS 2 and 3, vs in Pickcode where you write 2 + 3, and the expression is in an invalid state before you enter the 3. Rewriting 2 + 3 to 2 + (2 + 1) is really hard when you have to think in prefix notation. One advantage that we have is when there are syntax errors, they are necessarily at the expression level, so in the worst case the student can just scrap the line and start over, vs in plain text where the error message for a mismatched paren could land lines later.