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> Does Findlib support ppx-style preprocessors?
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>Does Findlib support ppx-style preprocessors?</A
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> <SPAN
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> Yes, but there is only little
documentation.</P
><P
>Since findlib-1.5, ppx-style preprocessors are supported
to some extent. A package can now define a "ppx" property which is simply
a command to run as preprocessor (the command gets the marshalled AST
as input, and must generate the transformed AST in its output; see the
-ppx option of ocamlc/ocamlopt). A META file can simply look like:
<PRE
CLASS="PROGRAMLISTING"
>ppx = "./command"</PRE
>
when "command" is installed in the package directory (but you can also
omit "./" to search it, and you can prefix it with "@name/" if the command
is taken from another package "name").</P
><P
>For more complex scenarios, additional options or
arguments for the ppx preprocessor can be specified in descendant
packages with the "ppxopt" property. Package "A" might provide a
generic ppx preprocessor with a META file containing
<PRE
CLASS="PROGRAMLISTING"
>ppx = "./generic_ppx"</PRE
>
Package B might instantiate that preprocessor with
<PRE
CLASS="PROGRAMLISTING"
>requires = "A"
ppxopt = "A,ppx_b.cmo"</PRE
>
In this case "ocamlfind ocamlc -package B" would
add <TT
CLASS="LITERAL"
>-ppx "path_to_A/genric_ppx ppx_b.cmo"</TT
> to
the ocamlc invocation. The format of the "ppxopt" property is
specified in the findlib reference manual.</P
><P
>This feature is still a bit experimental.</P
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