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\section{Version numbers}
\label{sec:versions}

A CM library can carry a version number.  Version numbers are
specified in parentheses after the keyword {\tt Library} as non-empty
dot-separated sequences of non-negative integers.  Example:

\begin{verbatim}
  Library (1.4.1.4.2.1.3.5)
      structure Sqrt2
  is
      sqrt2.sml
\end{verbatim}

\subsection{How versions are compared}

Version numbers are compared lexicographically, dot-separated
component by dot-separated component, from left to right.  The
components themselves are compared numerically.

\subsection{Version checking}

An importing library or library component can specify which version of
the imported library it would like to see.  See the discussion is
section~\ref{sec:toolparam:cm} for how this is done.  Where a version
number is requested, an error is signalled if one of the following is
true:

\begin{itemize}
\item the imported library does not carry a version number
\item the imported library's version number is smaller than the
one requested
\item the imported library's version number has a first component
(known as the ``major'' version number) that is greater than the one
requested
\end{itemize}

A warning (but no error) is issued if the imported library has the
same major version but the version as a whole is greater than the one
requested.

Note: {\it Version numbers should be incremented on every change to a
library.  The major version number should be increased on every change
that is not backward-compatible.}
