[boost] [Wave] Does it do phases?

From: Daryle Walker (darylew_at_[hidden])
Date: 2005-08-19 08:02:13

Wave is our C++ preprocessor, but preprocessing is the third phase of
translating a file.  (Looking at section 2.1 in the standard).  I have a gut
feeling that all the compilers out there mush the first three phases
together in parsing a file.  Glancing over the Wave docs gives me the same
impression about it.  Are either one of these feelings accurate (this
requires a separate answer for each parser)?  If the answer for Wave is
"yes", could we separate them, at least as an option?  I feel that this is
important so we can gain full understanding of each phases.  It may be more
complicated[1], and most likely slower, but it could represent a clean
implementation.  (BTW, what phases does Wave act like?)

The first two[2] phases are:

1.  Native characters that match basic source characters are converted as so
(including line breaks).  Trigraphs are expanded to basic source[3].  Other
characters are turned into internal Unicode expansions (i.e. act like
"\uXXXX" or \Uxxxxxxxx"[4]).
2.  The backslash-newline soft line-break combination are collapsed, folding
multiple native lines into one logical line.  We should spit out an error if
the folding creates Unicode escapes.  For non-empty files, we need to spit
out errors if the last line is not a hard line-break, either a non-newline
character or a backslash-newline combination is forbidden.

[1] Our "Wave-1" would convert the original text (iterators) into phase-1
tokens.  Our "Wave-2" would convert phase-1 token (iterators) into phase-2
tokens, etc.  Remember that any file-name and line/column positions will
have to be passed through each phase.
[2] I thought Wave just did phase-3, with phases 1 and 2 thrown in at the
same time.  But now I'm not sure which phase Wave stops at.  I don't think
it can go past phase-4, because doing phase-5 needs knowledge of the
destination platform.
[3] Only '?' characters that are part of a valid trigraph sequence are
converted; all others are left unchanged.
[4] But actual "\uXXXX" resolution doesn't happen until phase 5!

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT hotmail DOT com