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><A
NAME="AEN89"
>How a package directory looks like</A
></H1
><P
>Let us assume that the package p implements the modules M1 and M2. If
you compile m1.mli and m2.mli you get the corresponding binary files
m1.cmi and m2.cmi describing the interfaces of the modules. Of course,
these cmi files must go into the package directory. It is recommended
to put the source mli files into the directory, too, as they document
the interface.</P
><P
>Another product of the compilation are two cmo files, m1.cmo and
m2.cmo (we assume the bytecode compiler, the native compiler would
create m1.cmx and m2.cmx). It is possible to put these files directly
into the directory, but there is a better way. As it makes only sense
to use both modules (a very common assumption), they should first be
archived by doing</P
><PRE
CLASS="PROGRAMLISTING"
>ocamlc -a -o p.cma m1.cmo m2.cmo</PRE
><P
>The archive p.cma contains both cmo files, and preserves the order of
the files. Assumed that in M2 there is a reference to an entity in M1,
M2 depends on M1 and when linking a program using these modules, M1
must be mentioned first (e.g. ocamlc m1.cmo m2.cmo
program.ml)<A
NAME="AEN95"
HREF="#FTN.AEN95"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
>. If you create the archive p.cma it contains already
this dependency, and you need not to remember it when linking in the
p.cma.</P
><P
>So far the files m1.cmi, m2.cmi, and p.cma are needed, and m1.mli and
m2.mli are recommended. Usually there is another file in the
directory, META, containing additional information about the package.
In our example, META looks like</P
><PRE
CLASS="PROGRAMLISTING"
>description = "Our super-duper package"
requires = ""
version = "1"
archive(byte) = "p.cma"</PRE
><P
>The variable "requires" contains a list of packages that are
required by this package (the names may be separated by commas or
spaces). As our package, p, does not depend on any other package, this
list is empty. I'll explain what happens with non-empty lists below.</P
><P
>The variable "version" is simply a version string, and "description"
is a short comment on the package.</P
><P
>The variable "archive" denotes the files that have to be
actually linked in if the package is used. This is again a list of
(file) names. In contrast to the other variables, "archive" has a
condition, written in parentheses. This value of "archive" will only
be used if the predicate "byte" is true; this predicate is usually
given if the program is compiled to bytecode. If you have a native
archive, p.cmxa, of the two modules M1 and M2, you can add another
line to META:</P
><PRE
CLASS="PROGRAMLISTING"
>archive(native) = "p.cmxa"</PRE
><P
>The correct value for the "archive" variable is selected upon the
given set of predicates.</P
><P
>Many packages can also be loaded at runtime with the
<TT
CLASS="LITERAL"
>Fl_dynload</TT
> module. In this case, though, the
variable "plugin" is used instead of "archive", e.g.</P
><PRE
CLASS="PROGRAMLISTING"
>plugin(byte) = "p.cma"
plugin(native) = "p.cmxs"</PRE
><P
>(You can create p.cmxs from p.cmxa with
"ocamlopt -shared -linkall -o p.cmxs p.cmxa".) Note that "plugin" is entirely optional.</P
></DIV
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>Notes</H3
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>[1]</SPAN
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><P
>Note that C linkers usually require the reverse
order, but only for archive elements, i.e. files with suffix
.a.</P
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