
diff -r 2775062fd3a9 -r 2f4684e2ea95 doc-src/Codegen/Thy/document/Adaption.tex
--- /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:




