Why do some people use keywords for the clauses in the loop macro?

Question

Does it solve any problem? According to the first footnote of PCL, if not a keyword it interns the symbol in the current package. As all keywords are interned in the keyword package it would prevent multiple symbols being interned in different packages. But are there any other advantages? What problems does it create? (I'm guessing there must be a problem as it is not the prevalent convention)

Answer 1

No, the only advantage is to not end up with extra symbols in whatever package your code is read in.

This isn't a problem in and of itself, but it is one of those things that make (some) elemens of automatic introspection more difficult. If you are careful to use keywords for LOOP "keywords", you can then easily identify the names of all your functions, variables and macros by simply looking at the symbols interned in the package.

Answer 2

In lisp-aware editors, keywords are highlighted. Using keywords in loop helps highlight the loop structure.