--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/doc-src/Codegen/Thy/document/Adaption.tex Tue Mar 03 11:00:51 2009 +0100
@@ -0,0 +1,679 @@
+%
+\begin{isabellebody}%
+\def\isabellecontext{Adaption}%
+%
+\isadelimtheory
+%
+\endisadelimtheory
+%
+\isatagtheory
+\isacommand{theory}\isamarkupfalse%
+\ Adaption\isanewline
+\isakeyword{imports}\ Setup\isanewline
+\isakeyword{begin}%
+\endisatagtheory
+{\isafoldtheory}%
+%
+\isadelimtheory
+\isanewline
+%
+\endisadelimtheory
+%
+\isadeliminvisible
+\isanewline
+%
+\endisadeliminvisible
+%
+\isataginvisible
+\isacommand{setup}\isamarkupfalse%
+\ {\isacharverbatimopen}\ Code{\isacharunderscore}Target{\isachardot}extend{\isacharunderscore}target\ {\isacharparenleft}{\isachardoublequote}{\isasymSML}{\isachardoublequote}{\isacharcomma}\ {\isacharparenleft}{\isachardoublequote}SML{\isachardoublequote}{\isacharcomma}\ K\ I{\isacharparenright}{\isacharparenright}\ {\isacharverbatimclose}%
+\endisataginvisible
+{\isafoldinvisible}%
+%
+\isadeliminvisible
+%
+\endisadeliminvisible
+%
+\isamarkupsection{Adaption to target languages \label{sec:adaption}%
+}
+\isamarkuptrue%
+%
+\isamarkupsubsection{Adapting code generation%
+}
+\isamarkuptrue%
+%
+\begin{isamarkuptext}%
+The aspects of code generation introduced so far have two aspects
+ in common:
+
+ \begin{itemize}
+ \item They act uniformly, without reference to a specific
+ target language.
+ \item They are \emph{safe} in the sense that as long as you trust
+ the code generator meta theory and implementation, you cannot
+ produce programs that yield results which are not derivable
+ in the logic.
+ \end{itemize}
+
+ \noindent In this section we will introduce means to \emph{adapt} the serialiser
+ to a specific target language, i.e.~to print program fragments
+ in a way which accommodates \qt{already existing} ingredients of
+ a target language environment, for three reasons:
+
+ \begin{itemize}
+ \item improving readability and aesthetics of generated code
+ \item gaining efficiency
+ \item interface with language parts which have no direct counterpart
+ in \isa{HOL} (say, imperative data structures)
+ \end{itemize}
+
+ \noindent Generally, you should avoid using those features yourself
+ \emph{at any cost}:
+
+ \begin{itemize}
+ \item The safe configuration methods act uniformly on every target language,
+ whereas for adaption you have to treat each target language separate.
+ \item Application is extremely tedious since there is no abstraction
+ which would allow for a static check, making it easy to produce garbage.
+ \item More or less subtle errors can be introduced unconsciously.
+ \end{itemize}
+
+ \noindent However, even if you ought refrain from setting up adaption
+ yourself, already the \isa{HOL} comes with some reasonable default
+ adaptions (say, using target language list syntax). There also some
+ common adaption cases which you can setup by importing particular
+ library theories. In order to understand these, we provide some clues here;
+ these however are not supposed to replace a careful study of the sources.%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isamarkupsubsection{The adaption principle%
+}
+\isamarkuptrue%
+%
+\begin{isamarkuptext}%
+The following figure illustrates what \qt{adaption} is conceptually
+ supposed to be:
+
+ \begin{figure}[here]
+ \begin{tikzpicture}[scale = 0.5]
+ \tikzstyle water=[color = blue, thick]
+ \tikzstyle ice=[color = black, very thick, cap = round, join = round, fill = white]
+ \tikzstyle process=[color = green, semithick, ->]
+ \tikzstyle adaption=[color = red, semithick, ->]
+ \tikzstyle target=[color = black]
+ \foreach \x in {0, ..., 24}
+ \draw[style=water] (\x, 0.25) sin + (0.25, 0.25) cos + (0.25, -0.25) sin
+ + (0.25, -0.25) cos + (0.25, 0.25);
+ \draw[style=ice] (1, 0) --
+ (3, 6) node[above, fill=white] {logic} -- (5, 0) -- cycle;
+ \draw[style=ice] (9, 0) --
+ (11, 6) node[above, fill=white] {intermediate language} -- (13, 0) -- cycle;
+ \draw[style=ice] (15, -6) --
+ (19, 6) node[above, fill=white] {target language} -- (23, -6) -- cycle;
+ \draw[style=process]
+ (3.5, 3) .. controls (7, 5) .. node[fill=white] {translation} (10.5, 3);
+ \draw[style=process]
+ (11.5, 3) .. controls (15, 5) .. node[fill=white] (serialisation) {serialisation} (18.5, 3);
+ \node (adaption) at (11, -2) [style=adaption] {adaption};
+ \node at (19, 3) [rotate=90] {generated};
+ \node at (19.5, -5) {language};
+ \node at (19.5, -3) {library};
+ \node (includes) at (19.5, -1) {includes};
+ \node (reserved) at (16.5, -3) [rotate=72] {reserved}; % proper 71.57
+ \draw[style=process]
+ (includes) -- (serialisation);
+ \draw[style=process]
+ (reserved) -- (serialisation);
+ \draw[style=adaption]
+ (adaption) -- (serialisation);
+ \draw[style=adaption]
+ (adaption) -- (includes);
+ \draw[style=adaption]
+ (adaption) -- (reserved);
+ \end{tikzpicture}
+ \caption{The adaption principle}
+ \label{fig:adaption}
+ \end{figure}
+
+ \noindent In the tame view, code generation acts as broker between
+ \isa{logic}, \isa{intermediate\ language} and
+ \isa{target\ language} by means of \isa{translation} and
+ \isa{serialisation}; for the latter, the serialiser has to observe
+ the structure of the \isa{language} itself plus some \isa{reserved}
+ keywords which have to be avoided for generated code.
+ However, if you consider \isa{adaption} mechanisms, the code generated
+ by the serializer is just the tip of the iceberg:
+
+ \begin{itemize}
+ \item \isa{serialisation} can be \emph{parametrised} such that
+ logical entities are mapped to target-specific ones
+ (e.g. target-specific list syntax,
+ see also \secref{sec:adaption_mechanisms})
+ \item Such parametrisations can involve references to a
+ target-specific standard \isa{library} (e.g. using
+ the \isa{Haskell} \verb|Maybe| type instead
+ of the \isa{HOL} \isa{option} type);
+ if such are used, the corresponding identifiers
+ (in our example, \verb|Maybe|, \verb|Nothing|
+ and \verb|Just|) also have to be considered \isa{reserved}.
+ \item Even more, the user can enrich the library of the
+ target-language by providing code snippets
+ (\qt{\isa{includes}}) which are prepended to
+ any generated code (see \secref{sec:include}); this typically
+ also involves further \isa{reserved} identifiers.
+ \end{itemize}
+
+ \noindent As figure \ref{fig:adaption} illustrates, all these adaption mechanisms
+ have to act consistently; it is at the discretion of the user
+ to take care for this.%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isamarkupsubsection{Common adaption patterns%
+}
+\isamarkuptrue%
+%
+\begin{isamarkuptext}%
+The \hyperlink{theory.HOL}{\mbox{\isa{HOL}}} \hyperlink{theory.Main}{\mbox{\isa{Main}}} theory already provides a code
+ generator setup
+ which should be suitable for most applications. Common extensions
+ and modifications are available by certain theories of the \isa{HOL}
+ library; beside being useful in applications, they may serve
+ as a tutorial for customising the code generator setup (see below
+ \secref{sec:adaption_mechanisms}).
+
+ \begin{description}
+
+ \item[\hyperlink{theory.Code-Integer}{\mbox{\isa{Code{\isacharunderscore}Integer}}}] represents \isa{HOL} integers by big
+ integer literals in target languages.
+ \item[\hyperlink{theory.Code-Char}{\mbox{\isa{Code{\isacharunderscore}Char}}}] represents \isa{HOL} characters by
+ character literals in target languages.
+ \item[\hyperlink{theory.Code-Char-chr}{\mbox{\isa{Code{\isacharunderscore}Char{\isacharunderscore}chr}}}] like \isa{Code{\isacharunderscore}Char},
+ but also offers treatment of character codes; includes
+ \hyperlink{theory.Code-Char}{\mbox{\isa{Code{\isacharunderscore}Char}}}.
+ \item[\hyperlink{theory.Efficient-Nat}{\mbox{\isa{Efficient{\isacharunderscore}Nat}}}] \label{eff_nat} implements natural numbers by integers,
+ which in general will result in higher efficiency; pattern
+ matching with \isa{{\isadigit{0}}} / \isa{Suc}
+ is eliminated; includes \hyperlink{theory.Code-Integer}{\mbox{\isa{Code{\isacharunderscore}Integer}}}
+ and \hyperlink{theory.Code-Index}{\mbox{\isa{Code{\isacharunderscore}Index}}}.
+ \item[\hyperlink{theory.Code-Index}{\mbox{\isa{Code{\isacharunderscore}Index}}}] provides an additional datatype
+ \isa{index} which is mapped to target-language built-in integers.
+ Useful for code setups which involve e.g. indexing of
+ target-language arrays.
+ \item[\hyperlink{theory.Code-Message}{\mbox{\isa{Code{\isacharunderscore}Message}}}] provides an additional datatype
+ \isa{message{\isacharunderscore}string} which is isomorphic to strings;
+ \isa{message{\isacharunderscore}string}s are mapped to target-language strings.
+ Useful for code setups which involve e.g. printing (error) messages.
+
+ \end{description}
+
+ \begin{warn}
+ When importing any of these theories, they should form the last
+ items in an import list. Since these theories adapt the
+ code generator setup in a non-conservative fashion,
+ strange effects may occur otherwise.
+ \end{warn}%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isamarkupsubsection{Parametrising serialisation \label{sec:adaption_mechanisms}%
+}
+\isamarkuptrue%
+%
+\begin{isamarkuptext}%
+Consider the following function and its corresponding
+ SML code:%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\isatagquote
+\isacommand{primrec}\isamarkupfalse%
+\ in{\isacharunderscore}interval\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}nat\ {\isasymtimes}\ nat\ {\isasymRightarrow}\ nat\ {\isasymRightarrow}\ bool{\isachardoublequoteclose}\ \isakeyword{where}\isanewline
+\ \ {\isachardoublequoteopen}in{\isacharunderscore}interval\ {\isacharparenleft}k{\isacharcomma}\ l{\isacharparenright}\ n\ {\isasymlongleftrightarrow}\ k\ {\isasymle}\ n\ {\isasymand}\ n\ {\isasymle}\ l{\isachardoublequoteclose}%
+\endisatagquote
+{\isafoldquote}%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\isadeliminvisible
+%
+\endisadeliminvisible
+%
+\isataginvisible
+%
+\endisataginvisible
+{\isafoldinvisible}%
+%
+\isadeliminvisible
+%
+\endisadeliminvisible
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\isatagquote
+%
+\begin{isamarkuptext}%
+\isatypewriter%
+\noindent%
+\hspace*{0pt}structure Example = \\
+\hspace*{0pt}struct\\
+\hspace*{0pt}\\
+\hspace*{0pt}datatype nat = Zero{\char95}nat | Suc of nat;\\
+\hspace*{0pt}\\
+\hspace*{0pt}datatype boola = True | False;\\
+\hspace*{0pt}\\
+\hspace*{0pt}fun anda x True = x\\
+\hspace*{0pt} ~| anda x False = False\\
+\hspace*{0pt} ~| anda True x = x\\
+\hspace*{0pt} ~| anda False x = False;\\
+\hspace*{0pt}\\
+\hspace*{0pt}fun less{\char95}nat m (Suc n) = less{\char95}eq{\char95}nat m n\\
+\hspace*{0pt} ~| less{\char95}nat n Zero{\char95}nat = False\\
+\hspace*{0pt}and less{\char95}eq{\char95}nat (Suc m) n = less{\char95}nat m n\\
+\hspace*{0pt} ~| less{\char95}eq{\char95}nat Zero{\char95}nat n = True;\\
+\hspace*{0pt}\\
+\hspace*{0pt}fun in{\char95}interval (k,~l) n = anda (less{\char95}eq{\char95}nat k n) (less{\char95}eq{\char95}nat n l);\\
+\hspace*{0pt}\\
+\hspace*{0pt}end;~(*struct Example*)%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\endisatagquote
+{\isafoldquote}%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\begin{isamarkuptext}%
+\noindent Though this is correct code, it is a little bit unsatisfactory:
+ boolean values and operators are materialised as distinguished
+ entities with have nothing to do with the SML-built-in notion
+ of \qt{bool}. This results in less readable code;
+ additionally, eager evaluation may cause programs to
+ loop or break which would perfectly terminate when
+ the existing SML \verb|bool| would be used. To map
+ the HOL \isa{bool} on SML \verb|bool|, we may use
+ \qn{custom serialisations}:%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\isatagquotett
+\isacommand{code{\isacharunderscore}type}\isamarkupfalse%
+\ bool\isanewline
+\ \ {\isacharparenleft}SML\ {\isachardoublequoteopen}bool{\isachardoublequoteclose}{\isacharparenright}\isanewline
+\isacommand{code{\isacharunderscore}const}\isamarkupfalse%
+\ True\ \isakeyword{and}\ False\ \isakeyword{and}\ {\isachardoublequoteopen}op\ {\isasymand}{\isachardoublequoteclose}\isanewline
+\ \ {\isacharparenleft}SML\ {\isachardoublequoteopen}true{\isachardoublequoteclose}\ \isakeyword{and}\ {\isachardoublequoteopen}false{\isachardoublequoteclose}\ \isakeyword{and}\ {\isachardoublequoteopen}{\isacharunderscore}\ andalso\ {\isacharunderscore}{\isachardoublequoteclose}{\isacharparenright}%
+\endisatagquotett
+{\isafoldquotett}%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\begin{isamarkuptext}%
+\noindent The \hyperlink{command.code-type}{\mbox{\isa{\isacommand{code{\isacharunderscore}type}}}} command takes a type constructor
+ as arguments together with a list of custom serialisations.
+ Each custom serialisation starts with a target language
+ identifier followed by an expression, which during
+ code serialisation is inserted whenever the type constructor
+ would occur. For constants, \hyperlink{command.code-const}{\mbox{\isa{\isacommand{code{\isacharunderscore}const}}}} implements
+ the corresponding mechanism. Each ``\verb|_|'' in
+ a serialisation expression is treated as a placeholder
+ for the type constructor's (the constant's) arguments.%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\isatagquote
+%
+\begin{isamarkuptext}%
+\isatypewriter%
+\noindent%
+\hspace*{0pt}structure Example = \\
+\hspace*{0pt}struct\\
+\hspace*{0pt}\\
+\hspace*{0pt}datatype nat = Zero{\char95}nat | Suc of nat;\\
+\hspace*{0pt}\\
+\hspace*{0pt}fun less{\char95}nat m (Suc n) = less{\char95}eq{\char95}nat m n\\
+\hspace*{0pt} ~| less{\char95}nat n Zero{\char95}nat = false\\
+\hspace*{0pt}and less{\char95}eq{\char95}nat (Suc m) n = less{\char95}nat m n\\
+\hspace*{0pt} ~| less{\char95}eq{\char95}nat Zero{\char95}nat n = true;\\
+\hspace*{0pt}\\
+\hspace*{0pt}fun in{\char95}interval (k,~l) n = (less{\char95}eq{\char95}nat k n) andalso (less{\char95}eq{\char95}nat n l);\\
+\hspace*{0pt}\\
+\hspace*{0pt}end;~(*struct Example*)%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\endisatagquote
+{\isafoldquote}%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\begin{isamarkuptext}%
+\noindent This still is not perfect: the parentheses
+ around the \qt{andalso} expression are superfluous.
+ Though the serialiser
+ by no means attempts to imitate the rich Isabelle syntax
+ framework, it provides some common idioms, notably
+ associative infixes with precedences which may be used here:%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\isatagquotett
+\isacommand{code{\isacharunderscore}const}\isamarkupfalse%
+\ {\isachardoublequoteopen}op\ {\isasymand}{\isachardoublequoteclose}\isanewline
+\ \ {\isacharparenleft}SML\ \isakeyword{infixl}\ {\isadigit{1}}\ {\isachardoublequoteopen}andalso{\isachardoublequoteclose}{\isacharparenright}%
+\endisatagquotett
+{\isafoldquotett}%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\isatagquote
+%
+\begin{isamarkuptext}%
+\isatypewriter%
+\noindent%
+\hspace*{0pt}structure Example = \\
+\hspace*{0pt}struct\\
+\hspace*{0pt}\\
+\hspace*{0pt}datatype nat = Zero{\char95}nat | Suc of nat;\\
+\hspace*{0pt}\\
+\hspace*{0pt}fun less{\char95}nat m (Suc n) = less{\char95}eq{\char95}nat m n\\
+\hspace*{0pt} ~| less{\char95}nat n Zero{\char95}nat = false\\
+\hspace*{0pt}and less{\char95}eq{\char95}nat (Suc m) n = less{\char95}nat m n\\
+\hspace*{0pt} ~| less{\char95}eq{\char95}nat Zero{\char95}nat n = true;\\
+\hspace*{0pt}\\
+\hspace*{0pt}fun in{\char95}interval (k,~l) n = less{\char95}eq{\char95}nat k n andalso less{\char95}eq{\char95}nat n l;\\
+\hspace*{0pt}\\
+\hspace*{0pt}end;~(*struct Example*)%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\endisatagquote
+{\isafoldquote}%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\begin{isamarkuptext}%
+\noindent The attentive reader may ask how we assert that no generated
+ code will accidentally overwrite. For this reason the serialiser has
+ an internal table of identifiers which have to be avoided to be used
+ for new declarations. Initially, this table typically contains the
+ keywords of the target language. It can be extended manually, thus avoiding
+ accidental overwrites, using the \hyperlink{command.code-reserved}{\mbox{\isa{\isacommand{code{\isacharunderscore}reserved}}}} command:%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\isatagquote
+\isacommand{code{\isacharunderscore}reserved}\isamarkupfalse%
+\ {\isachardoublequoteopen}{\isasymSML}{\isachardoublequoteclose}\ bool\ true\ false\ andalso%
+\endisatagquote
+{\isafoldquote}%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\begin{isamarkuptext}%
+\noindent Next, we try to map HOL pairs to SML pairs, using the
+ infix ``\verb|*|'' type constructor and parentheses:%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadeliminvisible
+%
+\endisadeliminvisible
+%
+\isataginvisible
+%
+\endisataginvisible
+{\isafoldinvisible}%
+%
+\isadeliminvisible
+%
+\endisadeliminvisible
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\isatagquotett
+\isacommand{code{\isacharunderscore}type}\isamarkupfalse%
+\ {\isacharasterisk}\isanewline
+\ \ {\isacharparenleft}SML\ \isakeyword{infix}\ {\isadigit{2}}\ {\isachardoublequoteopen}{\isacharasterisk}{\isachardoublequoteclose}{\isacharparenright}\isanewline
+\isacommand{code{\isacharunderscore}const}\isamarkupfalse%
+\ Pair\isanewline
+\ \ {\isacharparenleft}SML\ {\isachardoublequoteopen}{\isacharbang}{\isacharparenleft}{\isacharparenleft}{\isacharunderscore}{\isacharparenright}{\isacharcomma}{\isacharslash}\ {\isacharparenleft}{\isacharunderscore}{\isacharparenright}{\isacharparenright}{\isachardoublequoteclose}{\isacharparenright}%
+\endisatagquotett
+{\isafoldquotett}%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\begin{isamarkuptext}%
+\noindent The initial bang ``\verb|!|'' tells the serialiser
+ never to put
+ parentheses around the whole expression (they are already present),
+ while the parentheses around argument place holders
+ tell not to put parentheses around the arguments.
+ The slash ``\verb|/|'' (followed by arbitrary white space)
+ inserts a space which may be used as a break if necessary
+ during pretty printing.
+
+ These examples give a glimpse what mechanisms
+ custom serialisations provide; however their usage
+ requires careful thinking in order not to introduce
+ inconsistencies -- or, in other words:
+ custom serialisations are completely axiomatic.
+
+ A further noteworthy details is that any special
+ character in a custom serialisation may be quoted
+ using ``\verb|'|''; thus, in
+ ``\verb|fn '_ => _|'' the first
+ ``\verb|_|'' is a proper underscore while the
+ second ``\verb|_|'' is a placeholder.%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isamarkupsubsection{\isa{Haskell} serialisation%
+}
+\isamarkuptrue%
+%
+\begin{isamarkuptext}%
+For convenience, the default
+ \isa{HOL} setup for \isa{Haskell} maps the \isa{eq} class to
+ its counterpart in \isa{Haskell}, giving custom serialisations
+ for the class \isa{eq} (by command \hyperlink{command.code-class}{\mbox{\isa{\isacommand{code{\isacharunderscore}class}}}}) and its operation
+ \isa{eq{\isacharunderscore}class{\isachardot}eq}%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\isatagquotett
+\isacommand{code{\isacharunderscore}class}\isamarkupfalse%
+\ eq\isanewline
+\ \ {\isacharparenleft}Haskell\ {\isachardoublequoteopen}Eq{\isachardoublequoteclose}{\isacharparenright}\isanewline
+\isanewline
+\isacommand{code{\isacharunderscore}const}\isamarkupfalse%
+\ {\isachardoublequoteopen}op\ {\isacharequal}{\isachardoublequoteclose}\isanewline
+\ \ {\isacharparenleft}Haskell\ \isakeyword{infixl}\ {\isadigit{4}}\ {\isachardoublequoteopen}{\isacharequal}{\isacharequal}{\isachardoublequoteclose}{\isacharparenright}%
+\endisatagquotett
+{\isafoldquotett}%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\begin{isamarkuptext}%
+\noindent A problem now occurs whenever a type which
+ is an instance of \isa{eq} in \isa{HOL} is mapped
+ on a \isa{Haskell}-built-in type which is also an instance
+ of \isa{Haskell} \isa{Eq}:%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquote
+%
+\endisadelimquote
+%
+\isatagquote
+\isacommand{typedecl}\isamarkupfalse%
+\ bar\isanewline
+\isanewline
+\isacommand{instantiation}\isamarkupfalse%
+\ bar\ {\isacharcolon}{\isacharcolon}\ eq\isanewline
+\isakeyword{begin}\isanewline
+\isanewline
+\isacommand{definition}\isamarkupfalse%
+\ {\isachardoublequoteopen}eq{\isacharunderscore}class{\isachardot}eq\ {\isacharparenleft}x{\isasymColon}bar{\isacharparenright}\ y\ {\isasymlongleftrightarrow}\ x\ {\isacharequal}\ y{\isachardoublequoteclose}\isanewline
+\isanewline
+\isacommand{instance}\isamarkupfalse%
+\ \isacommand{by}\isamarkupfalse%
+\ default\ {\isacharparenleft}simp\ add{\isacharcolon}\ eq{\isacharunderscore}bar{\isacharunderscore}def{\isacharparenright}\isanewline
+\isanewline
+\isacommand{end}\isamarkupfalse%
+%
+\endisatagquote
+{\isafoldquote}%
+%
+\isadelimquote
+%
+\endisadelimquote
+\isanewline
+%
+\isadelimquotett
+\isanewline
+%
+\endisadelimquotett
+%
+\isatagquotett
+\isacommand{code{\isacharunderscore}type}\isamarkupfalse%
+\ bar\isanewline
+\ \ {\isacharparenleft}Haskell\ {\isachardoublequoteopen}Integer{\isachardoublequoteclose}{\isacharparenright}%
+\endisatagquotett
+{\isafoldquotett}%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\begin{isamarkuptext}%
+\noindent The code generator would produce
+ an additional instance, which of course is rejected by the \isa{Haskell}
+ compiler.
+ To suppress this additional instance, use
+ \isa{code{\isacharunderscore}instance}:%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\isatagquotett
+\isacommand{code{\isacharunderscore}instance}\isamarkupfalse%
+\ bar\ {\isacharcolon}{\isacharcolon}\ eq\isanewline
+\ \ {\isacharparenleft}Haskell\ {\isacharminus}{\isacharparenright}%
+\endisatagquotett
+{\isafoldquotett}%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\isamarkupsubsection{Enhancing the target language context \label{sec:include}%
+}
+\isamarkuptrue%
+%
+\begin{isamarkuptext}%
+In rare cases it is necessary to \emph{enrich} the context of a
+ target language; this is accomplished using the \hyperlink{command.code-include}{\mbox{\isa{\isacommand{code{\isacharunderscore}include}}}}
+ command:%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\isatagquotett
+\isacommand{code{\isacharunderscore}include}\isamarkupfalse%
+\ Haskell\ {\isachardoublequoteopen}Errno{\isachardoublequoteclose}\isanewline
+{\isacharverbatimopen}errno\ i\ {\isacharequal}\ error\ {\isacharparenleft}{\isachardoublequote}Error\ number{\isacharcolon}\ {\isachardoublequote}\ {\isacharplus}{\isacharplus}\ show\ i{\isacharparenright}{\isacharverbatimclose}\isanewline
+\isanewline
+\isacommand{code{\isacharunderscore}reserved}\isamarkupfalse%
+\ Haskell\ Errno%
+\endisatagquotett
+{\isafoldquotett}%
+%
+\isadelimquotett
+%
+\endisadelimquotett
+%
+\begin{isamarkuptext}%
+\noindent Such named \isa{include}s are then prepended to every generated code.
+ Inspect such code in order to find out how \hyperlink{command.code-include}{\mbox{\isa{\isacommand{code{\isacharunderscore}include}}}} behaves
+ with respect to a particular target language.%
+\end{isamarkuptext}%
+\isamarkuptrue%
+%
+\isadelimtheory
+%
+\endisadelimtheory
+%
+\isatagtheory
+\isacommand{end}\isamarkupfalse%
+%
+\endisatagtheory
+{\isafoldtheory}%
+%
+\isadelimtheory
+%
+\endisadelimtheory
+\isanewline
+\end{isabellebody}%
+%%% Local Variables:
+%%% mode: latex
+%%% TeX-master: "root"
+%%% End: