Replaced F94 with F12

% !TeX root = forth.tex

\chapter{The optional Exception word set} % 9

\wordlist{exception}

\throwdef{-36}{invalid file position}

\throwdef{-37}{file I/O exception}

\throwdef{-38}{non-existent file}

\throwdef{-39}{unexpected end of file}

			\end{minipage} &

			\begin{minipage}[t]{\colwidth}

\throwdef{-39}{unexpected end of file}

\throwdef{-40}{invalid \word[core]{BASE} for floating point conversion}

\throwdef{-41}{loss of precision}

\throwdef{-42}{floating-point divide by zero}

\throwdef{-75}{\word[file]{WRITE-FILE}}

\throwdef{-76}{\word[file]{WRITE-LINE}}

\throwdef{-77}{Malformed xchar}

\throwdef[substitute]{-78}{\word[string]{SUBSTITUTE}}

\throwdef[substitute]{-79}{\word[string]{REPLACES}}

			\end{minipage}

			\\[-2ex] \hline\hline

		\end{tabular}

\section{Compliance and labeling} % 9.5

\cbstart\patch{F94}

\subsection[Forth systems]{ANS\strike{3.5}{25} Forth systems} % 9.5.1

\cbstart\patch{F12}

\subsection[Forth-\snapshot systems]{Forth-\snapshot\strike{-1}{25} systems} % 9.5.1

\cbend

The phrase ``Providing the Exception word set'' shall be appended to

appended to the label of any Standard System that provides all of

the Exception and Exception Extensions word sets.

\cbstart\patch{F94}

\subsection[Forth programs]{ANS\strike{3.5}{25} Forth programs} % 9.5.2

\cbstart\patch{F12}

\subsection[Forth-\snapshot programs]{Forth-\snapshot\strike{-1}{25} programs} % 9.5.2

\cbend

The phrase ``Requiring the Exception word set'' shall be appended

\see \rref{exception:THROW}{}.

	\begin{implement} % I.9.1.0875 CATCH

	\dffamily

\cbstart\patch{ed12}

\uline{%

		This sample implementation of \word{CATCH} uses the non-standard

		words described below.  They or their equivalents are available in many

		systems.  Other implementation strategies, including directly saving the

		value of \word[core]{DEPTH}, are possible if such words are not available.}

		\begin{quote}

		\uline{\texttt{SP@}} \stack{}{\uline{addr}}

			\uline{returns the address corresponding to the top of data stack.}

		\uline{\texttt{SP!}} \stack{\uline{addr}}{}

			\uline{sets the stack pointer to \emph{addr}, thus restoring the stack

			depth to the same depth that existed just before \emph{addr} was

			acquired by executing \texttt{SP@}.}

		\uline{\texttt{RP@}} \stack{}{\uline{addr}}

			\uline{returns the address corresponding to the top of return stack.}

		\uline{\texttt{RP!}} \stack{\uline{addr}}{}

			\uline{sets the return stack pointer to \emph{addr}, thus restoring the

			return stack depth to the same depth that existed just before

			\emph{addr} was acquired by executing \texttt{RP@}.}

		\end{quote}

		\ttfamily

		\begin{tabbing}

		\tab \= \tab \= \hspace{7em} \= ( saved-sp ) \= \kill

		\uline{\word{VARIABLE} HANDLER ~ 0 HANDLER \word{!}} ~ \uline{\word{bs} \textdf{last exception handler}} \\[\parskip]

		\+ \uline{\word{:} \word{CATCH} ~ \word{p} xt -{}- exception\# | 0 )} \uline{\word{bs} \textdf{return addr on stack}} \\

			\uline{SP@ \word{toR}}					\>\> \uline{\word{p} xt )}\> \uline{\word{bs} \textdf{save data stack pointer}} \\

			\uline{HANDLER \word{@} \word{toR}}	\>\> \uline{\word{p} xt )}\> \uline{\word{bs} \textdf{and previous handler}} \\

			\uline{RP@ HANDLER \word{!}}			\>\> \uline{\word{p} xt )}\> \uline{\word{bs} \textdf{set current handler}} \\

			\uline{\word{EXECUTE}}					\>\> \uline{\word{p} )}	\> \uline{\word{bs} \textdf{execute returns if no} THROW} \\

			\uline{\word{Rfrom} HANDLER \word{!}}	\>\> \uline{\word{p} )}	\> \uline{\word{bs} \textdf{restore previous handler}} \\

			\uline{\word{Rfrom} \word{DROP}}		\>\> \uline{\word{p} )}	\> \uline{\word{bs} \textdf{discard saved stack ptr}} \\

		\-	\uline{0}								\>\> \uline{\word{p} 0 )}	\> \uline{\word{bs} \textdf{normal completion}} \\

		\uline{\word{;}}

		\end{tabbing}

\uline{%

		In a multi-tasking system, the \texttt{HANDLER} variable should be in

		the per-task variable area (i.e., a user variable).}

\uline{%

		This sample implementation does not explicitly handle the case in

		which \word{CATCH} has never been called (i.e., the \word{ABORT}

		behavior). One solution would be to execute a \word{CATCH} within

		\word{QUIT}, so that there is always an ``exception handler of last

		resort'' present, as shown in \iref{core:QUIT}{}.}

\cbend

	\end{implement}

	\begin{testing}

		See \tref{exception:THROW}{}.

	\end{testing}

		\setwordlist{exception}

	\end{rationale}

	\begin{implement}

\cbstart\patch{ed12}

		\uline{\textdf{This is the counter part to \iref{exception:CATCH}{}.}}

		\begin{tabbing}

		\tab \= \tab \= \hspace{7em} \= ( saved-sp ) \= \kill

		\+ \uline{\word{:} \word{THROW}} \uline{\word{p} ??? exception\# -{}- ??? exception\# )} \\

			\+ \uline{\word{qDUP} \word{IF}}			\>		\> \uline{\word{p} exc\# )}	\> \uline{\word{bs} 0 THROW \textdf{is no-op}} \\

				\uline{HANDLER \word{@} RP!}				\> \uline{\word{p} exc\# )}	\> \uline{\word{bs} \textdf{restore prev return stack}} \\

				\uline{\word{Rfrom} HANDLER \word{!}}		\> \uline{\word{p} exc\# )}	\> \uline{\word{bs} \textdf{restore prev handler}} \\

				\uline{\word{Rfrom} \word{SWAP} \word{toR}}	\> \uline{\word{p} saved-sp )}\> \uline{\word{bs} exc\# \textdf{on return stack}} \\

				\uline{SP! \word{DROP} \word{Rfrom}}		\> \uline{\word{p} exc\# )}	\> \uline{\word{bs} \textdf{restore stack}} \\

				\uline{\word{bs} \textdf{Return to the caller of CATCH because return}} \\

				\uline{\word{bs} \textdf{stack is restored to the state that existed}} \\

			\-	\uline{\word{bs} \textdf{when CATCH began execution}} \\

		\- \uline{\word{THEN}} \\

		\uline{\word{;}}

		\end{tabbing}

\cbend

	\end{implement}

	\begin{testing} \ttfamily

		\word{DECIMAL}

		\test{c1}{1 2 3 9 0} \tab \word{bs} \textdf{No THROW executed}

		\word{:} t2 8 0 \word{THROW} \word{;} \\

		\word{:} c2 1 2 \word{[']} t2 \word{CATCH} \word{;}

		\word{:} c2 1 2 \word{[']} t2 \word{CATCH} \word{;} \\

		\test{c2}{1 2 8 0} \tab \word{bs} \textdf{0 THROW does nothing}

		\word{:} t3 7 8 9 99 \word{THROW} \word{;} \\

\see \wref{core:ABORT}{ABORT}.

	\begin{implement} % I.9.1.0875 CATCH

		\place{ed12}{\word{:} \word{ABORT} ~ -1 \word{THROW} ~ \word{;}}

	\end{implement}

	\begin{testing}

		See \tref{exception:ABORTq}{}.

	\end{testing}