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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
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> Does Findlib support camlp4?
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN461"
>Does Findlib support camlp4?</A
></H1
><P
> <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>Short answer:</I
></SPAN
> Yes, but there is only little
documentation.</P
><P
> Since Findlib-0.4, there is some experimental camlp4 support. For
example, the following compiler invocation chooses the revised syntax:
<PRE
CLASS="PROGRAMLISTING"
>ocamlfind ocamlc -syntax camlp4r -package camlp4 -c file.ml</PRE
>
As you can see, camlp4 must be included as package, and the
-syntax option must specify which syntax is selected (either
<TT
CLASS="LITERAL"
>camlp4o</TT
> or <TT
CLASS="LITERAL"
>camlp4r</TT
>).</P
><P
> If you want to pass additional options to the preprocessor,
you can use the <TT
CLASS="LITERAL"
>-ppopt</TT
> option:
<PRE
CLASS="PROGRAMLISTING"
>ocamlfind ocamlc -syntax camlp4r -package camlp4 -ppopt pa_ifdef.cmo -c file.ml</PRE
>
</P
><P
>From the toploop, the following commands work:
<PRE
CLASS="PROGRAMLISTING"
>$ ocaml
Objective Caml version 3.07+2
# #use "./topfind";;
- : unit = ()
Findlib has been successfully loaded. Additional directives:
#require "package";; to load a package
#list;; to list the available packages
#camlp4o;; to load camlp4 (standard syntax)
#camlp4r;; to load camlp4 (revised syntax)
#predicates "p,q,...";; to set these predicates
Topfind.reset();; to force that packages will be reloaded
#thread;; to enable threads
- : unit = ()
# #camlp4o;; (* or camlp4r *)
/opt/godi/lib/ocaml/std-lib/camlp4: added to search path
/opt/godi/lib/ocaml/std-lib/camlp4/camlp4o.cma: loaded
Camlp4 Parsing version 3.07+2
# _</PRE
> </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN474"
>The concept</A
></H2
><P
>If you have a <TT
CLASS="LITERAL"
>-syntax</TT
> option on the command line,
ocamlfind will generate a <TT
CLASS="LITERAL"
>-pp</TT
> parameter and pass it to the
invoked compiler. This is performed as follows: The specified packages are
inspected under a certain set of predicates, the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>syntax
predicates</I
></SPAN
>. The syntax predicates are <TT
CLASS="LITERAL"
>syntax</TT
>,
<TT
CLASS="LITERAL"
>preprocessor</TT
>, and the predicates following
<TT
CLASS="LITERAL"
>-syntax</TT
>. The predicate <TT
CLASS="LITERAL"
>syntax</TT
> simply
means that the <TT
CLASS="LITERAL"
>-syntax</TT
> option has been specified.
The predicate <TT
CLASS="LITERAL"
>preprocessor</TT
> means that the preprocessor
command is being constructed. The predicates added by
<TT
CLASS="LITERAL"
>-syntax</TT
> may be used to distinguish between syntax variants
(currently <TT
CLASS="LITERAL"
>camlp4o</TT
> and <TT
CLASS="LITERAL"
>camlp4r</TT
>).</P
><P
>The packages are searched for a variable <TT
CLASS="LITERAL"
>preprocessor</TT
>;
normally the <TT
CLASS="LITERAL"
>camlp4</TT
> package defines it as (see its META
file):
<PRE
CLASS="PROGRAMLISTING"
>preprocessor = "camlp4 -nolib"</PRE
>
Now that the name of the preprocessor command is known, the arguments of the
command are looked up. The META files are evaluated under the syntax
predicates, and all <TT
CLASS="LITERAL"
>archive</TT
> variables are collected and
passed as arguments to the preprocessor. For example, the camlp4 package
defines:
<PRE
CLASS="PROGRAMLISTING"
>archive(syntax,preprocessor,camlp4o) = "pa_o.cmo pa_op.cmo pr_dump.cmo"
archive(syntax,preprocessor,camlp4r) = "pa_r.cmo pa_rp.cmo pr_dump.cmo"</PRE
>
Note that the predicate <TT
CLASS="LITERAL"
>preprocessor</TT
> prevents ocamlfind from
including these archives into the regular list of archives to link.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN496"
>How to write a META file for your own syntax extension</A
></H2
><P
>Suppose you have two archives: <TT
CLASS="LITERAL"
>pa_myext.cma</TT
> contains the
extension code of camlp4, and <TT
CLASS="LITERAL"
>run_myext.cma</TT
> contains runtime
material that must be present in programs compiled with your extensions. Your
META file should look as follows:
<PRE
CLASS="PROGRAMLISTING"
>requires = "camlp4"
archive(syntax,toploop) = "pa_myext.cma run_myext.cma"
archive(syntax,preprocessor) = "pa_myext.cma"
archive(syntax,byte) = "run_myext.cma"
archive(syntax,native) = "run_myext.cmxa"</PRE
>
You may add dependencies on <TT
CLASS="LITERAL"
>camlp4o</TT
> or
<TT
CLASS="LITERAL"
>camlp4r</TT
> if you have archives only working for one of the two
syntax variants.</P
><P
>To compile a program using your syntax extension package, one should use:
<PRE
CLASS="PROGRAMLISTING"
>ocamlfind ocamlc -package yourname -syntax variant ...</PRE
></P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN506"
>Example</A
></H2
><P
>The package <TT
CLASS="LITERAL"
>xstrp4</TT
> defines a syntax extension allowing
$-substitutions in OCaml strings. Version 1.0 of this package takes advantage
from the new camlp4 support of findlib; you may have a look at it for an
example.</P
><P
>You can find <TT
CLASS="LITERAL"
>xstrp4</TT
>
<A
HREF="/projects/xstrp4.html"
TARGET="_top"
>here</A
>.</P
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