semantic.tex

由matlab开发的hybrid系统的描述语言

\chapter{Semantic Checks}
\label{sem_check_c}



The syntax of \hysdel{} is defined in the grammar. The parser only accepts input that is syntactically correct.
However, this does not mean that it is a correct \hysdel{} source. The input also has to be semantically correct.
Checking this is done immediately after the parsing step.

\section{Basic Checks}

Semantic checks are implemented in the methods called \function{semantic\_checks}. The following checks are
performed:
\begin{itemize}
\item in \cppclass{Var\_symbol}:
    \begin{itemize}
        \item variables must not be defined twice.
        \item variable definitions must not be circular. (e.g., a=b; b=c; c=a; is not allowed)
       \end{itemize}
\item in \cppclass{Expr}: \begin{itemize}
    \item arguments of operators have the right type (real or Boolean).
    \item no output variable is used.
\end{itemize}
\item in \cppclass{Item}: The semantic conditions mentioned in section \ref{Item_section} must be fulfilled (the grammar guarantees that the variables have the right type).
\item in \cppclass{Min\_max\_eps}: Minimum, maximum and epsilon must be constant.
\end{itemize}

\section{Argument Range Checks}

Mathematical operators have a domain of definition. For example, a division by zero is not allowed, therefore the
domain of definition of '$/$' is $\mathbb{R} \times \mathbb{R}\setminus \{0\}$.  The
\hysdel{} compiler has to check that all arguments are within the domain. \method{Expr}{arg\_range\_check\_matlab}
performs these checks.

What kind of checks are possible depends on the arguments and fall in three categories:
\begin{itemize}
\item the argument contains variables: no check is possible
\item the argument is constant but contains symbolic variables: create \matlab{} code to check range when symbolic
parameters are known.
\item the argument is constant and contains no symbolic variables: checks can be performed at compile time,
violations result in compilation errors.
\end{itemize}

The following range checks are implemented:
\begin{itemize}
\item Division by zero
\item Logarithm of a non positive number
\item Square root of a negative number
\end{itemize}


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