clasue goaltype parsing

[lyhlbyl]

current convention for clause gt paring is that if the fisr letter is lower case then string (except for key workds), if upper case then variable. But sometimes, we need to parse a string with upper case, for example:
c(Not)

[ggrov]

This should be a variable or you will break everything. two options I can think of,

• one is to wrap such special cases e.g. string(Not)
• one is to use e.g. "Not" or 'Not'-> we currently use " " for terms, but we can just use a different symbol there?

[yibo-liang]

How about using a leading $ or # for a term, and plain word for string?