Pre-Processing
==============

   The pre-processor:
   * adjusts and removes extra whitespace.  It leaves one space or tab
     before the keywords on a line, and turns any other whitespace on
     the line into a single space.

   * removes all comments, replacing them with a single space, or an
     appropriate number of newlines.

   * converts character constants into the appropriate numeric values.

   Excess whitespace, comments, and character constants cannot be used
in the portions of the input text that are not pre-processed.

   If the first line of an input file is `#NO_APP' or the `-f' option
is given, the input file will not be pre-processed.  Within such an
input file, parts of the file can be pre-processed by putting a line
that says `#APP' before the text that should be pre-processed, and
putting a line that says `#NO_APP' after them.  This feature is mainly
intend to support `asm' statements in compilers whose output normally
does not need to be pre-processed.