\section{THE CLE-2000 CONTROL LANGUAGE}

The CLE-2000 control language allows  loops, conditional testing and
macro-processor capabilities to be included in the generalized driver input
deck. A reversed polish notation (RPN) calculator named {\tt EVALUATE} is also
provided. An example of conditional testing is shown in the following example
involving two modules:

\vskip 0.4cm

\noindent\begin{tabular}{|l|}
\hline \\
{\tt INTEGER INDEX ;} \\
{\tt MODULE MOD1: MOD2: ;} \\
. \\
. \\
. \\
{\tt EVALUATE INDEX := 0 ;} \\
{\tt REPEAT} \\
{\tt ~~~~~EVALUATE INDEX := INDEX 1 + ;} \\
{\tt ~~~~~IF INDEX 3 > THEN} \\
{\tt ~~~~~~~~~~}{\sl (list of output objects)} {\tt := MOD1:} {\sl (list of input objects) {\tt ::} (data input for {\tt MOD1:})} {\tt ; }\\
{\tt ~~~~~ELSE} \\
{\tt ~~~~~~~~~~}{\sl (list of output objects)} {\tt := MOD2:} {\sl (list of input objects) {\tt ::} (data input for {\tt MOD2:})} {\tt ;} \\
{\tt ~~~~~ENDIF ;} \\
{\tt UNTIL INDEX 7 >= ;} \\
\\ \\ \hline
\end{tabular}

\vskip 0.4cm

An input deck will be built as a collection of 
\begin{itemize}
\item {\tt PARAMETER}, {\tt MODULE}, {\tt PROCEDURE}, {\tt LINKED}$\_${\tt LIST}, {\tt XSM}$\_${\tt FILE}, {\tt SEQ}$\_${\tt BINARY}, {\tt SEQ}$\_${\tt ASCII},
{\tt DIRECT}$\_${\tt ACCESS}, {\tt HDF5}$\_${\tt FILE}, {\tt INTEGER}, {\tt REAL}, {\tt CHARACTER}, {\tt DOUBLE} and {\tt LOGICAL} declarations;
\item {\tt MODULE} and {\tt PROCEDURE} calls;
\item {\tt EVALUATE} statements, {\tt ECHO} statements and conditional logic involving variables.
\end{itemize}

This type of programming provides the user with much more flexibility  than
the conventional approaches. It is possible to build new applications without
recompilation, simply by changing the order of the module calls and by making
modifications to the conditional logic. It is very simple to develop a
user-defined function even if this possibility is not programmed into any
module.

The CLE-2000 control language brings the following capabilities to any code built around the generalized driver:

\begin{itemize}
\item {\tt INTEGER}, {\tt REAL}, {\tt CHARACTER}, {\tt DOUBLE} and  {\tt
LOGICAL} declarations to contain control language and macro-processor variables.

\item macro processor variables. For example, it is possible to define a variable {\tt VAR1} as equal to a real number and to use {\tt <<VAR1>>} in place of this real number later on.

\item reversed polish notation calculator. A calculator is called each time the statement {\tt EVALUATE} is used. For example, the statement
  \begin{verbatim}
EVALUATE VAR1 := 4.0 6.0 + ;
  \end{verbatim}
would assign the result 10.0 to the variable {\tt VAR1}. Logical operations are fully supported.

\item a simple printer. For example, the variable {\tt VAR1} can be printed using the command
  \begin{verbatim}
ECHO VAR1 ;
  \end{verbatim}

\item three types of control loops. The available control loops are:

\begin{itemize}
\item {\tt IF} {\sl (logical expression)} {\tt THEN} {\sl (user instructions)} {\tt ELSE} {\sl (user instructions)} {\tt ENDIF ;}
\item {\tt REPEAT} {\sl (user instructions)} {\tt UNTIL} {\sl (logical expression)} {\tt ;}
\item {\tt WHILE} {\sl (logical expression)} {\tt DO} {\sl (user instructions)} {\tt ENDWHILE ;}
\end{itemize}

\end{itemize}

\vskip 0.2cm

Note that the {\tt EVALUATE} and {\tt ECHO} statements are {\sl not} modules of the generalized driver. A few rules and constraints
should be known on order to write valid datasets:
\begin{itemize}
\item CLE-2000 script files ({\tt *.x2m} or {\tt *.c2m}) are UNIX {\sc ascii} files {\sl not DOS files}.
\item A line of CLE-2000 code cannot exceed 132 {\sc ascii} characters.
\item Only the first 120 {\sc ascii} characters are significant.
\item All {\sc ascii} characters following a ``{\tt *}'' or a ``{\tt !}'' are considered as comments.
\item All {\sc ascii} characters between ``{\tt (*}'' and ``{\tt *)}'' are considered as comments.
\item Character case is significant.
\item The space character ``~'' is the separator. It is obligatory.
\item Tab characters are forbidden (you should disable automatic tabs on the editor).
\item The main script has a ``{\tt .x2m}'' suffix. Called scripts have a ``{\tt .c2m}'' suffix.
\item If a script is contained in a UNIX file ``{\tt myscript.x2m}'' or ``{\tt myscript.c2m}'', its CLE-2000 name is ``{\tt myscript}''. This name cannot exceed 12 characters.
\end{itemize}