R4RS 6.6  (char-alphabetic? char)  ==>  boolean
          (char-numeric? char)     ==>  boolean
          (char-whitespace? char)  ==>  boolean
          (char-upper-case? char)  ==>  boolean
          (char-lower-case? char)  ==>  boolean

These procedures return #T if their arguments are alphabetic,
numeric, whitespace, upper case, or lower case characters, respectively,
otherwise they return #F. The following remarks, which are specific
to the ASCII character set, are intended only as a guide: The
alphabetic characters are the 52 upper and lower case letters. The
numeric characters are the ten decimal digits. The whitespace
characters are space, tab, line feed, form feed, and carriage return.
