I appreciate the design choice to limit the "optional" parameter indicator to a single character instead of the "&optional" keyword from Common Lisp. However, in my opinion the "o" keyword doesn't stand out as much as "?" would do. An example:
(fn foo (a b (o c 1)) <body>)
(fn foo (a b (? c 1)) <body>)
Mnemonically I think many people will agree with me that "?" is a better 1-character indicator for "optional". It can be read as "is the parameter supplied?".
The "?" choice seems so obvious and natural that I cannot believe is hasn't been considered during the language specification process, and it makes me think there must be some deep reason why it hasn't beeen chosen. Any comments?
In CL I use named keyword arguments much more than optional ones, so I would want to keep single character prefix for keywords. This leads to a possibility: (&& x) would signify optional, (& x) would signify keyword.
I think that people want comments to have value in them. The best example of why this might get downmodded is if you look at it on the comments page it just looks like +1 without any context. So in that case it looks like a pretty vacuous comment. I think that if you enjoy a submission just upmod it. If you have something to add to the conversation add it.