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Compilation units
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<H2 CLASS="section"><A NAME="htoc90">6.12</A> Compilation units</H2>
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<DIV CLASS="center"><TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD ALIGN=right NOWRAP>
<A NAME="unit-interface"></A>
<FONT COLOR=maroon><I><TT>unit-interface</TT></I></FONT></TD>
<TD ALIGN=right NOWRAP>::=</TD>
<TD ALIGN=left NOWRAP> { <FONT COLOR=maroon><I><a href="manual018.html#specification"><font color=maroon><TT>specification</TT></font></a></I></FONT> [<FONT COLOR=blue><TT>;;</TT></FONT>] }</TD>
</TR>
<TR><TD ALIGN=right NOWRAP>
<A NAME="unit-implementation"></A>
<FONT COLOR=maroon><I><TT>unit-implementation</TT></I></FONT></TD>
<TD ALIGN=right NOWRAP>::=</TD>
<TD ALIGN=left NOWRAP> { <FONT COLOR=maroon><I><a href="manual019.html#definition"><font color=maroon><TT>definition</TT></font></a></I></FONT> [<FONT COLOR=blue><TT>;;</TT></FONT>] }</TD>
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Compilation units bridge the module system and the separate
compilation system. A compilation unit is composed of two parts: an
interface and an implementation. The interface contains a sequence of
specifications, just as the inside of a <FONT COLOR=blue><TT>sig</TT></FONT> … <FONT COLOR=blue><TT>end</TT></FONT>
signature expression. The implementation contains a sequence of
definitions, just as the inside of a <FONT COLOR=blue><TT>struct</TT></FONT> … <FONT COLOR=blue><TT>end</TT></FONT> module
expression. A compilation unit also has a name <FONT COLOR=maroon><I><TT>unit-name</TT></I></FONT>, derived
from the names of the files containing the interface and the
implementation (see chapter <A HREF="manual022.html#c:camlc">8</A> for more details). A
compilation unit behaves roughly as the module definition
<DIV CLASS="center">
<FONT COLOR=blue><TT>module</TT> <FONT COLOR=maroon><TT><I>unit-name</I></TT></FONT> <TT>:</TT> <TT>sig</TT> <FONT COLOR=maroon><TT><I>unit-interface</I></TT></FONT> <TT>end</TT> <TT>=</TT>
<TT>struct</TT> <FONT COLOR=maroon><TT><I>unit-implementation</I></TT></FONT> <TT>end</TT></FONT>
</DIV><BR>
<BR>
A compilation unit can refer to other compilation units by their
names, as if they were regular modules. For instance, if <TT>U</TT> is a
compilation unit that defines a type <TT>t</TT>, other compilation units can
refer to that type under the name <TT>U.t</TT>; they can also refer to <TT>U</TT> as
a whole structure. Except for names of other compilation units, a unit
interface or unit implementation must not have any other free variables.
In other terms, the type-checking and compilation of an interface or
implementation proceeds in the initial environment
<DIV CLASS="center">
<FONT COLOR=maroon><I><TT>name</TT></I></FONT><SUB>1</SUB> <FONT COLOR=blue><TT>:</TT> <TT>sig</TT></FONT> <FONT COLOR=maroon><I><TT>interface</TT></I></FONT><SUB>1</SUB> <FONT COLOR=blue><TT>end</TT></FONT> …
<I><FONT COLOR=maroon><TT>name</TT></FONT><SUB>n</SUB></I> <FONT COLOR=blue><TT>:</TT> <TT>sig</TT></FONT> <I><FONT COLOR=maroon><TT>interface</TT></FONT><SUB>n</SUB></I> <FONT COLOR=blue><TT>end</TT></FONT>
</DIV>
where <FONT COLOR=maroon><I><TT>name</TT></I></FONT><SUB>1</SUB> … <I><FONT COLOR=maroon><TT>name</TT></FONT><SUB>n</SUB></I> are the names of the other
compilation units available in the search path (see
chapter <A HREF="manual022.html#c:camlc">8</A> for more details) and <FONT COLOR=maroon><I><TT>interface</TT></I></FONT><SUB>1</SUB> …
<I><FONT COLOR=maroon><TT>interface</TT></FONT><SUB>n</SUB></I> are their respective interfaces.
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