[plt-scheme] contract naming conventions

Greetings, all.

Have we established any (de facto) naming conventions for contracts?

I've found it useful to define the following contracts for use in my
programs, and I'm not entirely sure that I like the -? naming
convention: after all, they're not exactly predicates, since I cannot
directly apply them to arguments.

  ;; contract that recognizes arbitrary s-expressions.
  (define sexp?
    (flat-rec-contract sexp
                       (cons/p sexp sexp)
                       null?
                       number?
                       symbol?
                       string?
                       boolean?
                       char?))

  (define predicate? (any? . -> . boolean?))

Also, while the /c and /p suffixes seem to be used for functions from
contracts to contracts, is there any convention over which gets used
when?

Thanks,

Richard