.TH CPPHS 1 2004-10-01 "cpphs version 0.9" "User Manual"

.SH NAME
cpphs \- liberalised cpp-a-like preprocessor for Haskell

.SH SYNOPSIS
.B cpphs
[\fIFILENAME\fR|\fIOPTION\fR]...

.SH DESCRIPTION
.ds c \fIcpphs\fP
\*c is a liberalised re-implementation of
.B cpp (1),
the C pre-processor, in and for Haskell.
.PP
Why re-implement cpp?  Rightly or wrongly, the C pre-processor is
widely used in Haskell source code.  It enables conditional compilation
for different compilers, different versions of the same compiler,
and different OS platforms.  It is also occasionally used for its
macro language, which can enable certain forms of platform-specific
detail-filling, such as the tedious boilerplate generation of instance
definitions and FFI declarations.  However, there are two problems with
cpp, aside from the obvious aesthetic ones:
.IP
For some Haskell systems, notably Hugs on Windows, a true cpp
is not available by default.
.IP
Even for the other Haskell systems, the common cpp provided by
the gcc 3.x series is changing subtly in ways that are
incompatible with Haskell's syntax.  There have always been
problems with, for instance, string gaps, and prime characters
in identifiers.  These problems are only going to get worse.
.PP
So, it seemed right to attempt to provide an alternative to cpp,
both more compatible with Haskell, and itself written in Haskell so
that it can be distributed with compilers.
.PP
\*c is pretty-much feature-complete,
and compatible with the
.B \-traditional
style of cpp.
It has two modes:
.IP
conditional compilation only (\fB\-\-nomacro\fR),
.IP
and full macro-expansion (default).
.PP
In
.B \-\-nomacro
mode, \*c performs only conditional compilation actions, i.e.
\fB#include\fR's, \fB#if\fR's, and \fB#ifdef\fR's are processed
according to text-replacement
definitions (both command-line and internal), but no parameterised
macro expansion is performed.  In full compatibility mode (the
default), textual replacements and macro expansions are also processed
in the remaining body of non-cpp text.
.PP
Working Features:
.TP
.B #ifdef
simple conditional compilation
.TP
.B #if
the full boolean language of defined(), &&, ||, ==, etc.
.TP
.B #elif
chained conditionals
.TP
.B #define
in-line definitions (text replacements and macros)
.TP
.B #undef
in-line revocation of definitions
.TP
.B #include
file inclusion
.TP
.B #line
line number directives
.TP
.B \\\\n
line continuations within all # directives
.TP
.B /**/
token catenation within a macro definition
.TP
.B ##
ANSI-style token catenation
.TP
.B #
ANSI-style token stringisation
.TP
.B __FILE__
special text replacement for DIY error messages
.TP
.B __LINE__
special text replacement for DIY error messages
.TP
.B __DATE__
special text replacement
.TP
.B __TIME__
special text replacement
.PP
Macro expansion is recursive.  Redefinition of a macro name does not
generate a warning.  Macros can be defined on the command-line with
.B \-D
just like textual replacements.  Macro names are permitted to be
Haskell identifiers e.g. with the prime \(ga and backtick \(aa characters,
which is slightly looser than in C, but they still may not include
operator symbols.
.PP
Numbering of lines in the output is preserved so that any later
processor can give meaningful error messages.  When a file is
\fB#include\fR'd, \*c inserts
.B #line
directives for the same reason. Numbering should be correct
even in the presence of line continuations. If you don't want
.B #line
directives in the final output, use the
.B \-\-noline
option.
.PP
Any syntax errors in cpp directives gives a message to stderr and
halts the program.  Failure to find a #include'd file produces a
warning to stderr, but processing continues.
.PP
You can give any number of filenames on the command-line.  The
results are catenated on standard output.
.TP
.B \-D\fIsym\fR
define a textual replacement (default value is 1)
.TP
.B \-Dsym=\fIval\fR
define a textual replacement with a specific value
.TP
.B \-I\fIpath\fR
add a directory to the search path for #include's
.TP
.B \-O\fIfile\fR
specify a file for output (default is stdout)
.TP
.B \-\-nomacro
only process #ifdef's and #include's,
                      do not expand macros
.TP
.B \-\-noline
remove #line droppings from the output
.TP
.B \-\-strip
convert C-style comments to whitespace, even outside
                      cpp directives
.TP
.B \-\-hashes
recognise the ANSI # stringise operator, and ## for
                      token catenation, within macros
.TP
.B \-\-text
treat the input as plain text, not Haskell code
.TP
.B \-\-layout
preserve newlines within macro expansions
.TP
.B \-\-unlit
remove literate-style comments
.TP
.B \-\-version
report version number of cpphs and stop
.PP
There are NO textual replacements defined by default.  (Normal cpp
usually has definitions for machine, OS, etc.  These could easily
be added to the cpphs source code if you wish.)  The search path is
searched in order of the
.B \-I
options, except that the directory of the
calling file, then the current directory, are always searched first.
Again, there is no default search path (and again, this could easily
be changed).

.SH "DIFFERENCES FROM CPP"
.PP
In general, cpphs is based on the
.B \-traditional
behaviour, not ANSI C, and has the following main differences from the
standard cpp.

.B General
.PP
The
.B #
that introduces any cpp directive must be in the first
column of a line (whereas ANSI permits whitespace before the
.B #
).
.PP
Generates the
.B "#line \fIn\fR \(dq\fIfilename\fR\(dq"
syntax, not the
.B "# \fIn\fR \(dq\fIfilename\fR\(dq"
variant.
.PP
C comments are only removed from within cpp directives.  They are
not stripped from other text.  Consider for instance that in
Haskell, all of the following are valid operator symbols:
.B /*  */  */*
However, you can turn on C-comment removal with the
.B \-\-strip
option.

.B Macro language
.PP
Accepts
.B /**/
for token-pasting in a macro definition.
However,
.B /* */
(with any text between the open/close comment) inserts whitespace.
.PP
The ANSI
.B ##
token-pasting operator is available with
the
.B \-\-hashes
flag.  This is to avoid misinterpreting
any valid Haskell operator of the same name.
.PP
Replaces a macro formal parameter with the actual, even inside a
string (double or single quoted).  This is \-traditional behaviour,
not supported in ANSI.
.PP
Recognises the
.B #
stringisation operator in a macro
definition only if you use the
.B \-\-hashes
option.  (It is
an ANSI addition, only needed because quoted stringisation (above)
is prohibited by ANSI.)
.PP
Preserves whitespace within a textual replacement definition
exactly (modulo newlines), but leading and trailing space is eliminated.
.PP
Preserves whitespace within a macro definition (and trailing it)
exactly (modulo newlines), but leading space is eliminated.
.PP
Preserves whitespace within macro call arguments exactly
(including newlines), but leading and trailing space is eliminated.
.PP
With the
.B \-\-layout
option, line continuations in a textual
replacement or macro definition are preserved as line-breaks in the
macro call.  (Useful for layout-sensitive code in Haskell.)

.SH BUGS
Bug reports, and any other feedback, should be sent to
Malcolm Wallace <Malcolm.Wallace@cs.york.ac.uk>
.SH COPYRIGHT
Copyright \(co 2004-2005 Malcolm Wallace,
except for ParseLib (Copyright \(co 1995 Graham Hutton and Erik Meijer).
.PP
The library modules in cpphs are distributed under
the terms of the LGPL. If that's a problem for you, contact me to make
other arrangements. The application module
.B Main.hs
itself is GPL.
.SH "SEE ALSO"
.BR cpp (1)

.SH AUTHOR

This manual page was written, based on \fBindex.html\fR,
by Ian Lynagh <igloo@debian.org> for the Debian
system (but may be used by others).