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Compilation units
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<H2>5.12 Compilation units</H2>
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<TABLE CELLSPACING=2 CELLPADDING=0>
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<TT><I><FONT COLOR=maroon>unit-interface</FONT></I></TT></TD>
<TD ALIGN=right NOWRAP>::=</TD>
<TD ALIGN=left NOWRAP> { <TT><I><FONT COLOR=maroon>specification</FONT></I></TT> [<TT><FONT COLOR=blue>;;</FONT></TT>] }</TD>
</TR>
<TR><TD ALIGN=right NOWRAP>
<TT><I><FONT COLOR=maroon>unit-implementation</FONT></I></TT></TD>
<TD ALIGN=right NOWRAP>::=</TD>
<TD ALIGN=left NOWRAP> { <TT><I><FONT COLOR=maroon>definition</FONT></I></TT> [<TT><FONT COLOR=blue>;;</FONT></TT>] }</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 <TT><FONT COLOR=blue>sig</FONT></TT> ... <TT><FONT COLOR=blue>end</FONT></TT>
signature expression. The implementation contains a sequence of
definitions, just as the inside of a <TT><FONT COLOR=blue>struct</FONT></TT> ... <TT><FONT COLOR=blue>end</FONT></TT> module
expression. A compilation unit also has a name <TT><I><FONT COLOR=maroon>unit-name</FONT></I></TT>, derived
from the names of the files containing the interface and the
implementation (see chapter <A HREF="manual020.html#c:camlc">7</A> for more details). A
compilation unit behaves roughly as the module definition
<DIV ALIGN=center>
<TT><FONT COLOR=blue>module</FONT></TT> <TT><I><FONT COLOR=maroon>unit-name</FONT></I></TT> <TT><FONT COLOR=blue>:</FONT></TT> <TT><FONT COLOR=blue>sig</FONT></TT> <TT><I><FONT COLOR=maroon>unit-interface</FONT></I></TT> <TT><FONT COLOR=blue>end</FONT></TT> <TT><FONT COLOR=blue>=</FONT></TT>
<TT><FONT COLOR=blue>struct</FONT></TT> <TT><I><FONT COLOR=maroon>unit-implementation</FONT></I></TT> <TT><FONT COLOR=blue>end</FONT></TT>
</DIV><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 ALIGN=center>
<TT><I><FONT COLOR=maroon>name</FONT></I></TT><SUB><FONT SIZE=2>1</FONT></SUB> <TT><FONT COLOR=blue>:</FONT></TT> <TT><FONT COLOR=blue>sig</FONT></TT> <TT><I><FONT COLOR=maroon>interface</FONT></I></TT><SUB><FONT SIZE=2>1</FONT></SUB> <TT><FONT COLOR=blue>end</FONT></TT> ...
<TT><I><FONT COLOR=maroon>name</FONT></I></TT><SUB><FONT SIZE=2><I>n</I></FONT></SUB> <TT><FONT COLOR=blue>:</FONT></TT> <TT><FONT COLOR=blue>sig</FONT></TT> <TT><I><FONT COLOR=maroon>interface</FONT></I></TT><SUB><FONT SIZE=2><I>n</I></FONT></SUB> <TT><FONT COLOR=blue>end</FONT></TT>
</DIV>
where <TT><I><FONT COLOR=maroon>name</FONT></I></TT><SUB><FONT SIZE=2>1</FONT></SUB> ... <TT><I><FONT COLOR=maroon>name</FONT></I></TT><SUB><FONT SIZE=2><I>N</I></FONT></SUB> are the names of the other
compilation units available in the search path (see
chapter <A HREF="manual020.html#c:camlc">7</A> for more details) and <TT><I><FONT COLOR=maroon>interface</FONT></I></TT><SUB><FONT SIZE=2>1</FONT></SUB> ...
<TT><I><FONT COLOR=maroon>interface</FONT></I></TT><SUB><FONT SIZE=2><I>n</I></FONT></SUB> are their respective interfaces.
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