--- a/doc-src/IsarAdvanced/Classes/Thy/document/Classes.tex Mon Mar 02 16:58:39 2009 +0100
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
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-\begin{isabellebody}%
-\def\isabellecontext{Classes}%
-%
-\isadelimtheory
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-\endisadelimtheory
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-\isatagtheory
-\isacommand{theory}\isamarkupfalse%
-\ Classes\isanewline
-\isakeyword{imports}\ Main\ Setup\isanewline
-\isakeyword{begin}%
-\endisatagtheory
-{\isafoldtheory}%
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-\isadelimtheory
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-\endisadelimtheory
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-\isamarkupchapter{Haskell-style classes with Isabelle/Isar%
-}
-\isamarkuptrue%
-%
-\isamarkupsection{Introduction%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-Type classes were introduces by Wadler and Blott \cite{wadler89how}
- into the Haskell language, to allow for a reasonable implementation
- of overloading\footnote{throughout this tutorial, we are referring
- to classical Haskell 1.0 type classes, not considering
- later additions in expressiveness}.
- As a canonical example, a polymorphic equality function
- \isa{eq\ {\isasymColon}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ bool} which is overloaded on different
- types for \isa{{\isasymalpha}}, which is achieved by splitting introduction
- of the \isa{eq} function from its overloaded definitions by means
- of \isa{class} and \isa{instance} declarations:
-
- \begin{quote}
-
- \noindent\isa{class\ eq\ where}\footnote{syntax here is a kind of isabellized Haskell} \\
- \hspace*{2ex}\isa{eq\ {\isasymColon}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ bool}
-
- \medskip\noindent\isa{instance\ nat\ {\isasymColon}\ eq\ where} \\
- \hspace*{2ex}\isa{eq\ {\isadigit{0}}\ {\isadigit{0}}\ {\isacharequal}\ True} \\
- \hspace*{2ex}\isa{eq\ {\isadigit{0}}\ {\isacharunderscore}\ {\isacharequal}\ False} \\
- \hspace*{2ex}\isa{eq\ {\isacharunderscore}\ {\isadigit{0}}\ {\isacharequal}\ False} \\
- \hspace*{2ex}\isa{eq\ {\isacharparenleft}Suc\ n{\isacharparenright}\ {\isacharparenleft}Suc\ m{\isacharparenright}\ {\isacharequal}\ eq\ n\ m}
-
- \medskip\noindent\isa{instance\ {\isacharparenleft}{\isasymalpha}{\isasymColon}eq{\isacharcomma}\ {\isasymbeta}{\isasymColon}eq{\isacharparenright}\ pair\ {\isasymColon}\ eq\ where} \\
- \hspace*{2ex}\isa{eq\ {\isacharparenleft}x{\isadigit{1}}{\isacharcomma}\ y{\isadigit{1}}{\isacharparenright}\ {\isacharparenleft}x{\isadigit{2}}{\isacharcomma}\ y{\isadigit{2}}{\isacharparenright}\ {\isacharequal}\ eq\ x{\isadigit{1}}\ x{\isadigit{2}}\ {\isasymand}\ eq\ y{\isadigit{1}}\ y{\isadigit{2}}}
-
- \medskip\noindent\isa{class\ ord\ extends\ eq\ where} \\
- \hspace*{2ex}\isa{less{\isacharunderscore}eq\ {\isasymColon}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ bool} \\
- \hspace*{2ex}\isa{less\ {\isasymColon}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ bool}
-
- \end{quote}
-
- \noindent Type variables are annotated with (finitely many) classes;
- these annotations are assertions that a particular polymorphic type
- provides definitions for overloaded functions.
-
- Indeed, type classes not only allow for simple overloading
- but form a generic calculus, an instance of order-sorted
- algebra \cite{Nipkow-Prehofer:1993,nipkow-sorts93,Wenzel:1997:TPHOL}.
-
- From a software engeneering point of view, type classes
- roughly correspond to interfaces in object-oriented languages like Java;
- so, it is naturally desirable that type classes do not only
- provide functions (class parameters) but also state specifications
- implementations must obey. For example, the \isa{class\ eq}
- above could be given the following specification, demanding that
- \isa{class\ eq} is an equivalence relation obeying reflexivity,
- symmetry and transitivity:
-
- \begin{quote}
-
- \noindent\isa{class\ eq\ where} \\
- \hspace*{2ex}\isa{eq\ {\isasymColon}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ bool} \\
- \isa{satisfying} \\
- \hspace*{2ex}\isa{refl{\isacharcolon}\ eq\ x\ x} \\
- \hspace*{2ex}\isa{sym{\isacharcolon}\ eq\ x\ y\ {\isasymlongleftrightarrow}\ eq\ x\ y} \\
- \hspace*{2ex}\isa{trans{\isacharcolon}\ eq\ x\ y\ {\isasymand}\ eq\ y\ z\ {\isasymlongrightarrow}\ eq\ x\ z}
-
- \end{quote}
-
- \noindent From a theoretic point of view, type classes are lightweight
- modules; Haskell type classes may be emulated by
- SML functors \cite{classes_modules}.
- Isabelle/Isar offers a discipline of type classes which brings
- all those aspects together:
-
- \begin{enumerate}
- \item specifying abstract parameters together with
- corresponding specifications,
- \item instantiating those abstract parameters by a particular
- type
- \item in connection with a ``less ad-hoc'' approach to overloading,
- \item with a direct link to the Isabelle module system
- (aka locales \cite{kammueller-locales}).
- \end{enumerate}
-
- \noindent Isar type classes also directly support code generation
- in a Haskell like fashion.
-
- This tutorial demonstrates common elements of structured specifications
- and abstract reasoning with type classes by the algebraic hierarchy of
- semigroups, monoids and groups. Our background theory is that of
- Isabelle/HOL \cite{isa-tutorial}, for which some
- familiarity is assumed.
-
- Here we merely present the look-and-feel for end users.
- Internally, those are mapped to more primitive Isabelle concepts.
- See \cite{Haftmann-Wenzel:2006:classes} for more detail.%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isamarkupsection{A simple algebra example \label{sec:example}%
-}
-\isamarkuptrue%
-%
-\isamarkupsubsection{Class definition%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-Depending on an arbitrary type \isa{{\isasymalpha}}, class \isa{semigroup} introduces a binary operator \isa{{\isacharparenleft}{\isasymotimes}{\isacharparenright}} that is
- assumed to be associative:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{class}\isamarkupfalse%
-\ semigroup\ {\isacharequal}\isanewline
-\ \ \isakeyword{fixes}\ mult\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequoteclose}\ \ \ \ {\isacharparenleft}\isakeyword{infixl}\ {\isachardoublequoteopen}{\isasymotimes}{\isachardoublequoteclose}\ {\isadigit{7}}{\isadigit{0}}{\isacharparenright}\isanewline
-\ \ \isakeyword{assumes}\ assoc{\isacharcolon}\ {\isachardoublequoteopen}{\isacharparenleft}x\ {\isasymotimes}\ y{\isacharparenright}\ {\isasymotimes}\ z\ {\isacharequal}\ x\ {\isasymotimes}\ {\isacharparenleft}y\ {\isasymotimes}\ z{\isacharparenright}{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent This \hyperlink{command.class}{\mbox{\isa{\isacommand{class}}}} specification consists of two
- parts: the \qn{operational} part names the class parameter
- (\hyperlink{element.fixes}{\mbox{\isa{\isakeyword{fixes}}}}), the \qn{logical} part specifies properties on them
- (\hyperlink{element.assumes}{\mbox{\isa{\isakeyword{assumes}}}}). The local \hyperlink{element.fixes}{\mbox{\isa{\isakeyword{fixes}}}} and
- \hyperlink{element.assumes}{\mbox{\isa{\isakeyword{assumes}}}} are lifted to the theory toplevel,
- yielding the global
- parameter \isa{{\isachardoublequote}mult\ {\isasymColon}\ {\isasymalpha}{\isasymColon}semigroup\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequote}} and the
- global theorem \hyperlink{fact.semigroup.assoc:}{\mbox{\isa{semigroup{\isachardot}assoc{\isacharcolon}}}}~\isa{{\isachardoublequote}{\isasymAnd}x\ y\ z\ {\isasymColon}\ {\isasymalpha}{\isasymColon}semigroup{\isachardot}\ {\isacharparenleft}x\ {\isasymotimes}\ y{\isacharparenright}\ {\isasymotimes}\ z\ {\isacharequal}\ x\ {\isasymotimes}\ {\isacharparenleft}y\ {\isasymotimes}\ z{\isacharparenright}{\isachardoublequote}}.%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isamarkupsubsection{Class instantiation \label{sec:class_inst}%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-The concrete type \isa{int} is made a \isa{semigroup}
- instance by providing a suitable definition for the class parameter
- \isa{{\isacharparenleft}{\isasymotimes}{\isacharparenright}} and a proof for the specification of \hyperlink{fact.assoc}{\mbox{\isa{assoc}}}.
- This is accomplished by the \hyperlink{command.instantiation}{\mbox{\isa{\isacommand{instantiation}}}} target:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{instantiation}\isamarkupfalse%
-\ int\ {\isacharcolon}{\isacharcolon}\ semigroup\isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{definition}\isamarkupfalse%
-\isanewline
-\ \ mult{\isacharunderscore}int{\isacharunderscore}def{\isacharcolon}\ {\isachardoublequoteopen}i\ {\isasymotimes}\ j\ {\isacharequal}\ i\ {\isacharplus}\ {\isacharparenleft}j{\isasymColon}int{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{instance}\isamarkupfalse%
-\ \isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ i\ j\ k\ {\isacharcolon}{\isacharcolon}\ int\ \isacommand{have}\isamarkupfalse%
-\ {\isachardoublequoteopen}{\isacharparenleft}i\ {\isacharplus}\ j{\isacharparenright}\ {\isacharplus}\ k\ {\isacharequal}\ i\ {\isacharplus}\ {\isacharparenleft}j\ {\isacharplus}\ k{\isacharparenright}{\isachardoublequoteclose}\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\ \ \isacommand{then}\isamarkupfalse%
-\ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}{\isacharparenleft}i\ {\isasymotimes}\ j{\isacharparenright}\ {\isasymotimes}\ k\ {\isacharequal}\ i\ {\isasymotimes}\ {\isacharparenleft}j\ {\isasymotimes}\ k{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ mult{\isacharunderscore}int{\isacharunderscore}def\ \isacommand{{\isachardot}}\isamarkupfalse%
-\isanewline
-\isacommand{qed}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent \hyperlink{command.instantiation}{\mbox{\isa{\isacommand{instantiation}}}} allows to define class parameters
- at a particular instance using common specification tools (here,
- \hyperlink{command.definition}{\mbox{\isa{\isacommand{definition}}}}). The concluding \hyperlink{command.instance}{\mbox{\isa{\isacommand{instance}}}}
- opens a proof that the given parameters actually conform
- to the class specification. Note that the first proof step
- is the \hyperlink{method.default}{\mbox{\isa{default}}} method,
- which for such instance proofs maps to the \hyperlink{method.intro-classes}{\mbox{\isa{intro{\isacharunderscore}classes}}} method.
- This boils down an instance judgement to the relevant primitive
- proof goals and should conveniently always be the first method applied
- in an instantiation proof.
-
- From now on, the type-checker will consider \isa{int}
- as a \isa{semigroup} automatically, i.e.\ any general results
- are immediately available on concrete instances.
-
- \medskip Another instance of \isa{semigroup} are the natural numbers:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{instantiation}\isamarkupfalse%
-\ nat\ {\isacharcolon}{\isacharcolon}\ semigroup\isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{primrec}\isamarkupfalse%
-\ mult{\isacharunderscore}nat\ \isakeyword{where}\isanewline
-\ \ {\isachardoublequoteopen}{\isacharparenleft}{\isadigit{0}}{\isasymColon}nat{\isacharparenright}\ {\isasymotimes}\ n\ {\isacharequal}\ n{\isachardoublequoteclose}\isanewline
-\ \ {\isacharbar}\ {\isachardoublequoteopen}Suc\ m\ {\isasymotimes}\ n\ {\isacharequal}\ Suc\ {\isacharparenleft}m\ {\isasymotimes}\ n{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{instance}\isamarkupfalse%
-\ \isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ m\ n\ q\ {\isacharcolon}{\isacharcolon}\ nat\ \isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}m\ {\isasymotimes}\ n\ {\isasymotimes}\ q\ {\isacharequal}\ m\ {\isasymotimes}\ {\isacharparenleft}n\ {\isasymotimes}\ q{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{by}\isamarkupfalse%
-\ {\isacharparenleft}induct\ m{\isacharparenright}\ auto\isanewline
-\isacommand{qed}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent Note the occurence of the name \isa{mult{\isacharunderscore}nat}
- in the primrec declaration; by default, the local name of
- a class operation \isa{f} to instantiate on type constructor
- \isa{{\isasymkappa}} are mangled as \isa{f{\isacharunderscore}{\isasymkappa}}. In case of uncertainty,
- these names may be inspected using the \hyperlink{command.print-context}{\mbox{\isa{\isacommand{print{\isacharunderscore}context}}}} command
- or the corresponding ProofGeneral button.%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isamarkupsubsection{Lifting and parametric types%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-Overloaded definitions giving on class instantiation
- may include recursion over the syntactic structure of types.
- As a canonical example, we model product semigroups
- using our simple algebra:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{instantiation}\isamarkupfalse%
-\ {\isacharasterisk}\ {\isacharcolon}{\isacharcolon}\ {\isacharparenleft}semigroup{\isacharcomma}\ semigroup{\isacharparenright}\ semigroup\isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{definition}\isamarkupfalse%
-\isanewline
-\ \ mult{\isacharunderscore}prod{\isacharunderscore}def{\isacharcolon}\ {\isachardoublequoteopen}p\isactrlisub {\isadigit{1}}\ {\isasymotimes}\ p\isactrlisub {\isadigit{2}}\ {\isacharequal}\ {\isacharparenleft}fst\ p\isactrlisub {\isadigit{1}}\ {\isasymotimes}\ fst\ p\isactrlisub {\isadigit{2}}{\isacharcomma}\ snd\ p\isactrlisub {\isadigit{1}}\ {\isasymotimes}\ snd\ p\isactrlisub {\isadigit{2}}{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{instance}\isamarkupfalse%
-\ \isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ p\isactrlisub {\isadigit{1}}\ p\isactrlisub {\isadigit{2}}\ p\isactrlisub {\isadigit{3}}\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}{\isasymColon}semigroup\ {\isasymtimes}\ {\isasymbeta}{\isasymColon}semigroup{\isachardoublequoteclose}\isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}p\isactrlisub {\isadigit{1}}\ {\isasymotimes}\ p\isactrlisub {\isadigit{2}}\ {\isasymotimes}\ p\isactrlisub {\isadigit{3}}\ {\isacharequal}\ p\isactrlisub {\isadigit{1}}\ {\isasymotimes}\ {\isacharparenleft}p\isactrlisub {\isadigit{2}}\ {\isasymotimes}\ p\isactrlisub {\isadigit{3}}{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ mult{\isacharunderscore}prod{\isacharunderscore}def\ \isacommand{by}\isamarkupfalse%
-\ {\isacharparenleft}simp\ add{\isacharcolon}\ assoc{\isacharparenright}\isanewline
-\isacommand{qed}\isamarkupfalse%
-\ \ \ \ \ \ \isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent Associativity from product semigroups is
- established using
- the definition of \isa{{\isacharparenleft}{\isasymotimes}{\isacharparenright}} on products and the hypothetical
- associativity of the type components; these hypotheses
- are facts due to the \isa{semigroup} constraints imposed
- on the type components by the \hyperlink{command.instance}{\mbox{\isa{\isacommand{instance}}}} proposition.
- Indeed, this pattern often occurs with parametric types
- and type classes.%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isamarkupsubsection{Subclassing%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-We define a subclass \isa{monoidl} (a semigroup with a left-hand neutral)
- by extending \isa{semigroup}
- with one additional parameter \isa{neutral} together
- with its property:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{class}\isamarkupfalse%
-\ monoidl\ {\isacharequal}\ semigroup\ {\isacharplus}\isanewline
-\ \ \isakeyword{fixes}\ neutral\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}{\isachardoublequoteclose}\ {\isacharparenleft}{\isachardoublequoteopen}{\isasymone}{\isachardoublequoteclose}{\isacharparenright}\isanewline
-\ \ \isakeyword{assumes}\ neutl{\isacharcolon}\ {\isachardoublequoteopen}{\isasymone}\ {\isasymotimes}\ x\ {\isacharequal}\ x{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent Again, we prove some instances, by
- providing suitable parameter definitions and proofs for the
- additional specifications. Observe that instantiations
- for types with the same arity may be simultaneous:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{instantiation}\isamarkupfalse%
-\ nat\ \isakeyword{and}\ int\ {\isacharcolon}{\isacharcolon}\ monoidl\isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{definition}\isamarkupfalse%
-\isanewline
-\ \ neutral{\isacharunderscore}nat{\isacharunderscore}def{\isacharcolon}\ {\isachardoublequoteopen}{\isasymone}\ {\isacharequal}\ {\isacharparenleft}{\isadigit{0}}{\isasymColon}nat{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{definition}\isamarkupfalse%
-\isanewline
-\ \ neutral{\isacharunderscore}int{\isacharunderscore}def{\isacharcolon}\ {\isachardoublequoteopen}{\isasymone}\ {\isacharequal}\ {\isacharparenleft}{\isadigit{0}}{\isasymColon}int{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{instance}\isamarkupfalse%
-\ \isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ n\ {\isacharcolon}{\isacharcolon}\ nat\isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}{\isasymone}\ {\isasymotimes}\ n\ {\isacharequal}\ n{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ neutral{\isacharunderscore}nat{\isacharunderscore}def\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\isacommand{next}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ k\ {\isacharcolon}{\isacharcolon}\ int\isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}{\isasymone}\ {\isasymotimes}\ k\ {\isacharequal}\ k{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ neutral{\isacharunderscore}int{\isacharunderscore}def\ mult{\isacharunderscore}int{\isacharunderscore}def\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\isacommand{qed}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{instantiation}\isamarkupfalse%
-\ {\isacharasterisk}\ {\isacharcolon}{\isacharcolon}\ {\isacharparenleft}monoidl{\isacharcomma}\ monoidl{\isacharparenright}\ monoidl\isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{definition}\isamarkupfalse%
-\isanewline
-\ \ neutral{\isacharunderscore}prod{\isacharunderscore}def{\isacharcolon}\ {\isachardoublequoteopen}{\isasymone}\ {\isacharequal}\ {\isacharparenleft}{\isasymone}{\isacharcomma}\ {\isasymone}{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{instance}\isamarkupfalse%
-\ \isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ p\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}{\isasymColon}monoidl\ {\isasymtimes}\ {\isasymbeta}{\isasymColon}monoidl{\isachardoublequoteclose}\isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}{\isasymone}\ {\isasymotimes}\ p\ {\isacharequal}\ p{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ neutral{\isacharunderscore}prod{\isacharunderscore}def\ mult{\isacharunderscore}prod{\isacharunderscore}def\ \isacommand{by}\isamarkupfalse%
-\ {\isacharparenleft}simp\ add{\isacharcolon}\ neutl{\isacharparenright}\isanewline
-\isacommand{qed}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent Fully-fledged monoids are modelled by another subclass
- which does not add new parameters but tightens the specification:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{class}\isamarkupfalse%
-\ monoid\ {\isacharequal}\ monoidl\ {\isacharplus}\isanewline
-\ \ \isakeyword{assumes}\ neutr{\isacharcolon}\ {\isachardoublequoteopen}x\ {\isasymotimes}\ {\isasymone}\ {\isacharequal}\ x{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{instantiation}\isamarkupfalse%
-\ nat\ \isakeyword{and}\ int\ {\isacharcolon}{\isacharcolon}\ monoid\ \isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{instance}\isamarkupfalse%
-\ \isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ n\ {\isacharcolon}{\isacharcolon}\ nat\isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}n\ {\isasymotimes}\ {\isasymone}\ {\isacharequal}\ n{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ neutral{\isacharunderscore}nat{\isacharunderscore}def\ \isacommand{by}\isamarkupfalse%
-\ {\isacharparenleft}induct\ n{\isacharparenright}\ simp{\isacharunderscore}all\isanewline
-\isacommand{next}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ k\ {\isacharcolon}{\isacharcolon}\ int\isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}k\ {\isasymotimes}\ {\isasymone}\ {\isacharequal}\ k{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ neutral{\isacharunderscore}int{\isacharunderscore}def\ mult{\isacharunderscore}int{\isacharunderscore}def\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\isacommand{qed}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{instantiation}\isamarkupfalse%
-\ {\isacharasterisk}\ {\isacharcolon}{\isacharcolon}\ {\isacharparenleft}monoid{\isacharcomma}\ monoid{\isacharparenright}\ monoid\isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{instance}\isamarkupfalse%
-\ \isacommand{proof}\isamarkupfalse%
-\ \isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ p\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}{\isasymColon}monoid\ {\isasymtimes}\ {\isasymbeta}{\isasymColon}monoid{\isachardoublequoteclose}\isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}p\ {\isasymotimes}\ {\isasymone}\ {\isacharequal}\ p{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ neutral{\isacharunderscore}prod{\isacharunderscore}def\ mult{\isacharunderscore}prod{\isacharunderscore}def\ \isacommand{by}\isamarkupfalse%
-\ {\isacharparenleft}simp\ add{\isacharcolon}\ neutr{\isacharparenright}\isanewline
-\isacommand{qed}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent To finish our small algebra example, we add a \isa{group} class
- with a corresponding instance:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{class}\isamarkupfalse%
-\ group\ {\isacharequal}\ monoidl\ {\isacharplus}\isanewline
-\ \ \isakeyword{fixes}\ inverse\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequoteclose}\ \ \ \ {\isacharparenleft}{\isachardoublequoteopen}{\isacharparenleft}{\isacharunderscore}{\isasymdiv}{\isacharparenright}{\isachardoublequoteclose}\ {\isacharbrackleft}{\isadigit{1}}{\isadigit{0}}{\isadigit{0}}{\isadigit{0}}{\isacharbrackright}\ {\isadigit{9}}{\isadigit{9}}{\isadigit{9}}{\isacharparenright}\isanewline
-\ \ \isakeyword{assumes}\ invl{\isacharcolon}\ {\isachardoublequoteopen}x{\isasymdiv}\ {\isasymotimes}\ x\ {\isacharequal}\ {\isasymone}{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{instantiation}\isamarkupfalse%
-\ int\ {\isacharcolon}{\isacharcolon}\ group\isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{definition}\isamarkupfalse%
-\isanewline
-\ \ inverse{\isacharunderscore}int{\isacharunderscore}def{\isacharcolon}\ {\isachardoublequoteopen}i{\isasymdiv}\ {\isacharequal}\ {\isacharminus}\ {\isacharparenleft}i{\isasymColon}int{\isacharparenright}{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{instance}\isamarkupfalse%
-\ \isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ i\ {\isacharcolon}{\isacharcolon}\ int\isanewline
-\ \ \isacommand{have}\isamarkupfalse%
-\ {\isachardoublequoteopen}{\isacharminus}i\ {\isacharplus}\ i\ {\isacharequal}\ {\isadigit{0}}{\isachardoublequoteclose}\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\ \ \isacommand{then}\isamarkupfalse%
-\ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}i{\isasymdiv}\ {\isasymotimes}\ i\ {\isacharequal}\ {\isasymone}{\isachardoublequoteclose}\isanewline
-\ \ \ \ \isacommand{unfolding}\isamarkupfalse%
-\ mult{\isacharunderscore}int{\isacharunderscore}def\ neutral{\isacharunderscore}int{\isacharunderscore}def\ inverse{\isacharunderscore}int{\isacharunderscore}def\ \isacommand{{\isachardot}}\isamarkupfalse%
-\isanewline
-\isacommand{qed}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isamarkupsection{Type classes as locales%
-}
-\isamarkuptrue%
-%
-\isamarkupsubsection{A look behind the scene%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-The example above gives an impression how Isar type classes work
- in practice. As stated in the introduction, classes also provide
- a link to Isar's locale system. Indeed, the logical core of a class
- is nothing else than a locale:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{class}\isamarkupfalse%
-\ idem\ {\isacharequal}\isanewline
-\ \ \isakeyword{fixes}\ f\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequoteclose}\isanewline
-\ \ \isakeyword{assumes}\ idem{\isacharcolon}\ {\isachardoublequoteopen}f\ {\isacharparenleft}f\ x{\isacharparenright}\ {\isacharequal}\ f\ x{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent essentially introduces the locale%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadeliminvisible
-\ %
-\endisadeliminvisible
-%
-\isataginvisible
-\isacommand{setup}\isamarkupfalse%
-\ {\isacharverbatimopen}\ Sign{\isachardot}add{\isacharunderscore}path\ {\isachardoublequote}foo{\isachardoublequote}\ {\isacharverbatimclose}%
-\endisataginvisible
-{\isafoldinvisible}%
-%
-\isadeliminvisible
-%
-\endisadeliminvisible
-\isanewline
-%
-\isadelimquote
-\isanewline
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{locale}\isamarkupfalse%
-\ idem\ {\isacharequal}\isanewline
-\ \ \isakeyword{fixes}\ f\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequoteclose}\isanewline
-\ \ \isakeyword{assumes}\ idem{\isacharcolon}\ {\isachardoublequoteopen}f\ {\isacharparenleft}f\ x{\isacharparenright}\ {\isacharequal}\ f\ x{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent together with corresponding constant(s):%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{consts}\isamarkupfalse%
-\ f\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}{\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent The connection to the type system is done by means
- of a primitive axclass%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadeliminvisible
-\ %
-\endisadeliminvisible
-%
-\isataginvisible
-\isacommand{setup}\isamarkupfalse%
-\ {\isacharverbatimopen}\ Sign{\isachardot}add{\isacharunderscore}path\ {\isachardoublequote}foo{\isachardoublequote}\ {\isacharverbatimclose}%
-\endisataginvisible
-{\isafoldinvisible}%
-%
-\isadeliminvisible
-%
-\endisadeliminvisible
-\isanewline
-%
-\isadelimquote
-\isanewline
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{axclass}\isamarkupfalse%
-\ idem\ {\isacharless}\ type\isanewline
-\ \ idem{\isacharcolon}\ {\isachardoublequoteopen}f\ {\isacharparenleft}f\ x{\isacharparenright}\ {\isacharequal}\ f\ x{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isadeliminvisible
-\ %
-\endisadeliminvisible
-%
-\isataginvisible
-\isacommand{setup}\isamarkupfalse%
-\ {\isacharverbatimopen}\ Sign{\isachardot}parent{\isacharunderscore}path\ {\isacharverbatimclose}%
-\endisataginvisible
-{\isafoldinvisible}%
-%
-\isadeliminvisible
-%
-\endisadeliminvisible
-%
-\begin{isamarkuptext}%
-\noindent together with a corresponding interpretation:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{interpretation}\isamarkupfalse%
-\ idem{\isacharunderscore}class{\isacharcolon}\isanewline
-\ \ idem\ {\isachardoublequoteopen}f\ {\isasymColon}\ {\isacharparenleft}{\isasymalpha}{\isasymColon}idem{\isacharparenright}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequoteclose}\isanewline
-\isacommand{proof}\isamarkupfalse%
-\ \isacommand{qed}\isamarkupfalse%
-\ {\isacharparenleft}rule\ idem{\isacharparenright}%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent This gives you at hand the full power of the Isabelle module system;
- conclusions in locale \isa{idem} are implicitly propagated
- to class \isa{idem}.%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadeliminvisible
-\ %
-\endisadeliminvisible
-%
-\isataginvisible
-\isacommand{setup}\isamarkupfalse%
-\ {\isacharverbatimopen}\ Sign{\isachardot}parent{\isacharunderscore}path\ {\isacharverbatimclose}%
-\endisataginvisible
-{\isafoldinvisible}%
-%
-\isadeliminvisible
-%
-\endisadeliminvisible
-%
-\isamarkupsubsection{Abstract reasoning%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-Isabelle locales enable reasoning at a general level, while results
- are implicitly transferred to all instances. For example, we can
- now establish the \isa{left{\isacharunderscore}cancel} lemma for groups, which
- states that the function \isa{{\isacharparenleft}x\ {\isasymotimes}{\isacharparenright}} is injective:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{lemma}\isamarkupfalse%
-\ {\isacharparenleft}\isakeyword{in}\ group{\isacharparenright}\ left{\isacharunderscore}cancel{\isacharcolon}\ {\isachardoublequoteopen}x\ {\isasymotimes}\ y\ {\isacharequal}\ x\ {\isasymotimes}\ z\ {\isasymlongleftrightarrow}\ y\ {\isacharequal}\ z{\isachardoublequoteclose}\isanewline
-\isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{assume}\isamarkupfalse%
-\ {\isachardoublequoteopen}x\ {\isasymotimes}\ y\ {\isacharequal}\ x\ {\isasymotimes}\ z{\isachardoublequoteclose}\isanewline
-\ \ \isacommand{then}\isamarkupfalse%
-\ \isacommand{have}\isamarkupfalse%
-\ {\isachardoublequoteopen}x{\isasymdiv}\ {\isasymotimes}\ {\isacharparenleft}x\ {\isasymotimes}\ y{\isacharparenright}\ {\isacharequal}\ x{\isasymdiv}\ {\isasymotimes}\ {\isacharparenleft}x\ {\isasymotimes}\ z{\isacharparenright}{\isachardoublequoteclose}\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\ \ \isacommand{then}\isamarkupfalse%
-\ \isacommand{have}\isamarkupfalse%
-\ {\isachardoublequoteopen}{\isacharparenleft}x{\isasymdiv}\ {\isasymotimes}\ x{\isacharparenright}\ {\isasymotimes}\ y\ {\isacharequal}\ {\isacharparenleft}x{\isasymdiv}\ {\isasymotimes}\ x{\isacharparenright}\ {\isasymotimes}\ z{\isachardoublequoteclose}\ \isacommand{using}\isamarkupfalse%
-\ assoc\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\ \ \isacommand{then}\isamarkupfalse%
-\ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}y\ {\isacharequal}\ z{\isachardoublequoteclose}\ \isacommand{using}\isamarkupfalse%
-\ neutl\ \isakeyword{and}\ invl\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\isacommand{next}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{assume}\isamarkupfalse%
-\ {\isachardoublequoteopen}y\ {\isacharequal}\ z{\isachardoublequoteclose}\isanewline
-\ \ \isacommand{then}\isamarkupfalse%
-\ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}x\ {\isasymotimes}\ y\ {\isacharequal}\ x\ {\isasymotimes}\ z{\isachardoublequoteclose}\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\isacommand{qed}\isamarkupfalse%
-%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent Here the \qt{\hyperlink{keyword.in}{\mbox{\isa{\isakeyword{in}}}} \isa{group}} target specification
- indicates that the result is recorded within that context for later
- use. This local theorem is also lifted to the global one \hyperlink{fact.group.left-cancel:}{\mbox{\isa{group{\isachardot}left{\isacharunderscore}cancel{\isacharcolon}}}} \isa{{\isachardoublequote}{\isasymAnd}x\ y\ z\ {\isasymColon}\ {\isasymalpha}{\isasymColon}group{\isachardot}\ x\ {\isasymotimes}\ y\ {\isacharequal}\ x\ {\isasymotimes}\ z\ {\isasymlongleftrightarrow}\ y\ {\isacharequal}\ z{\isachardoublequote}}. Since type \isa{int} has been made an instance of
- \isa{group} before, we may refer to that fact as well: \isa{{\isachardoublequote}{\isasymAnd}x\ y\ z\ {\isasymColon}\ int{\isachardot}\ x\ {\isasymotimes}\ y\ {\isacharequal}\ x\ {\isasymotimes}\ z\ {\isasymlongleftrightarrow}\ y\ {\isacharequal}\ z{\isachardoublequote}}.%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isamarkupsubsection{Derived definitions%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-Isabelle locales support a concept of local definitions
- in locales:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{primrec}\isamarkupfalse%
-\ {\isacharparenleft}\isakeyword{in}\ monoid{\isacharparenright}\ pow{\isacharunderscore}nat\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}nat\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequoteclose}\ \isakeyword{where}\isanewline
-\ \ {\isachardoublequoteopen}pow{\isacharunderscore}nat\ {\isadigit{0}}\ x\ {\isacharequal}\ {\isasymone}{\isachardoublequoteclose}\isanewline
-\ \ {\isacharbar}\ {\isachardoublequoteopen}pow{\isacharunderscore}nat\ {\isacharparenleft}Suc\ n{\isacharparenright}\ x\ {\isacharequal}\ x\ {\isasymotimes}\ pow{\isacharunderscore}nat\ n\ x{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent If the locale \isa{group} is also a class, this local
- definition is propagated onto a global definition of
- \isa{{\isachardoublequote}pow{\isacharunderscore}nat\ {\isasymColon}\ nat\ {\isasymRightarrow}\ {\isasymalpha}{\isasymColon}monoid\ {\isasymRightarrow}\ {\isasymalpha}{\isasymColon}monoid{\isachardoublequote}}
- with corresponding theorems
-
- \isa{pow{\isacharunderscore}nat\ {\isadigit{0}}\ x\ {\isacharequal}\ {\isasymone}\isasep\isanewline%
-pow{\isacharunderscore}nat\ {\isacharparenleft}Suc\ n{\isacharparenright}\ x\ {\isacharequal}\ x\ {\isasymotimes}\ pow{\isacharunderscore}nat\ n\ x}.
-
- \noindent As you can see from this example, for local
- definitions you may use any specification tool
- which works together with locales (e.g. \cite{krauss2006}).%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isamarkupsubsection{A functor analogy%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-We introduced Isar classes by analogy to type classes
- functional programming; if we reconsider this in the
- context of what has been said about type classes and locales,
- we can drive this analogy further by stating that type
- classes essentially correspond to functors which have
- a canonical interpretation as type classes.
- Anyway, there is also the possibility of other interpretations.
- For example, also \isa{list}s form a monoid with
- \isa{append} and \isa{{\isacharbrackleft}{\isacharbrackright}} as operations, but it
- seems inappropriate to apply to lists
- the same operations as for genuinely algebraic types.
- In such a case, we simply can do a particular interpretation
- of monoids for lists:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{interpretation}\isamarkupfalse%
-\ list{\isacharunderscore}monoid{\isacharbang}{\isacharcolon}\ monoid\ append\ {\isachardoublequoteopen}{\isacharbrackleft}{\isacharbrackright}{\isachardoublequoteclose}\isanewline
-\ \ \isacommand{proof}\isamarkupfalse%
-\ \isacommand{qed}\isamarkupfalse%
-\ auto%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent This enables us to apply facts on monoids
- to lists, e.g. \isa{{\isacharbrackleft}{\isacharbrackright}\ {\isacharat}\ x\ {\isacharequal}\ x}.
-
- When using this interpretation pattern, it may also
- be appropriate to map derived definitions accordingly:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{primrec}\isamarkupfalse%
-\ replicate\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}nat\ {\isasymRightarrow}\ {\isasymalpha}\ list\ {\isasymRightarrow}\ {\isasymalpha}\ list{\isachardoublequoteclose}\ \isakeyword{where}\isanewline
-\ \ {\isachardoublequoteopen}replicate\ {\isadigit{0}}\ {\isacharunderscore}\ {\isacharequal}\ {\isacharbrackleft}{\isacharbrackright}{\isachardoublequoteclose}\isanewline
-\ \ {\isacharbar}\ {\isachardoublequoteopen}replicate\ {\isacharparenleft}Suc\ n{\isacharparenright}\ xs\ {\isacharequal}\ xs\ {\isacharat}\ replicate\ n\ xs{\isachardoublequoteclose}\isanewline
-\isanewline
-\isacommand{interpretation}\isamarkupfalse%
-\ list{\isacharunderscore}monoid{\isacharbang}{\isacharcolon}\ monoid\ append\ {\isachardoublequoteopen}{\isacharbrackleft}{\isacharbrackright}{\isachardoublequoteclose}\ \isakeyword{where}\isanewline
-\ \ {\isachardoublequoteopen}monoid{\isachardot}pow{\isacharunderscore}nat\ append\ {\isacharbrackleft}{\isacharbrackright}\ {\isacharequal}\ replicate{\isachardoublequoteclose}\isanewline
-\isacommand{proof}\isamarkupfalse%
-\ {\isacharminus}\isanewline
-\ \ \isacommand{interpret}\isamarkupfalse%
-\ monoid\ append\ {\isachardoublequoteopen}{\isacharbrackleft}{\isacharbrackright}{\isachardoublequoteclose}\ \isacommand{{\isachardot}{\isachardot}}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}monoid{\isachardot}pow{\isacharunderscore}nat\ append\ {\isacharbrackleft}{\isacharbrackright}\ {\isacharequal}\ replicate{\isachardoublequoteclose}\isanewline
-\ \ \isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \ \ \isacommand{fix}\isamarkupfalse%
-\ n\isanewline
-\ \ \ \ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}monoid{\isachardot}pow{\isacharunderscore}nat\ append\ {\isacharbrackleft}{\isacharbrackright}\ n\ {\isacharequal}\ replicate\ n{\isachardoublequoteclose}\isanewline
-\ \ \ \ \ \ \isacommand{by}\isamarkupfalse%
-\ {\isacharparenleft}induct\ n{\isacharparenright}\ auto\isanewline
-\ \ \isacommand{qed}\isamarkupfalse%
-\isanewline
-\isacommand{qed}\isamarkupfalse%
-\ intro{\isacharunderscore}locales%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isamarkupsubsection{Additional subclass relations%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-Any \isa{group} is also a \isa{monoid}; this
- can be made explicit by claiming an additional
- subclass relation,
- together with a proof of the logical difference:%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\isatagquote
-\isacommand{subclass}\isamarkupfalse%
-\ {\isacharparenleft}\isakeyword{in}\ group{\isacharparenright}\ monoid\isanewline
-\isacommand{proof}\isamarkupfalse%
-\isanewline
-\ \ \isacommand{fix}\isamarkupfalse%
-\ x\isanewline
-\ \ \isacommand{from}\isamarkupfalse%
-\ invl\ \isacommand{have}\isamarkupfalse%
-\ {\isachardoublequoteopen}x{\isasymdiv}\ {\isasymotimes}\ x\ {\isacharequal}\ {\isasymone}{\isachardoublequoteclose}\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\ \ \isacommand{with}\isamarkupfalse%
-\ assoc\ {\isacharbrackleft}symmetric{\isacharbrackright}\ neutl\ invl\ \isacommand{have}\isamarkupfalse%
-\ {\isachardoublequoteopen}x{\isasymdiv}\ {\isasymotimes}\ {\isacharparenleft}x\ {\isasymotimes}\ {\isasymone}{\isacharparenright}\ {\isacharequal}\ x{\isasymdiv}\ {\isasymotimes}\ x{\isachardoublequoteclose}\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\ \ \isacommand{with}\isamarkupfalse%
-\ left{\isacharunderscore}cancel\ \isacommand{show}\isamarkupfalse%
-\ {\isachardoublequoteopen}x\ {\isasymotimes}\ {\isasymone}\ {\isacharequal}\ x{\isachardoublequoteclose}\ \isacommand{by}\isamarkupfalse%
-\ simp\isanewline
-\isacommand{qed}\isamarkupfalse%
-%
-\endisatagquote
-{\isafoldquote}%
-%
-\isadelimquote
-%
-\endisadelimquote
-%
-\begin{isamarkuptext}%
-\noindent The logical proof is carried out on the locale level.
- Afterwards it is propagated
- to the type system, making \isa{group} an instance of
- \isa{monoid} by adding an additional edge
- to the graph of subclass relations
- (cf.\ \figref{fig:subclass}).
-
- \begin{figure}[htbp]
- \begin{center}
- \small
- \unitlength 0.6mm
- \begin{picture}(40,60)(0,0)
- \put(20,60){\makebox(0,0){\isa{semigroup}}}
- \put(20,40){\makebox(0,0){\isa{monoidl}}}
- \put(00,20){\makebox(0,0){\isa{monoid}}}
- \put(40,00){\makebox(0,0){\isa{group}}}
- \put(20,55){\vector(0,-1){10}}
- \put(15,35){\vector(-1,-1){10}}
- \put(25,35){\vector(1,-3){10}}
- \end{picture}
- \hspace{8em}
- \begin{picture}(40,60)(0,0)
- \put(20,60){\makebox(0,0){\isa{semigroup}}}
- \put(20,40){\makebox(0,0){\isa{monoidl}}}
- \put(00,20){\makebox(0,0){\isa{monoid}}}
- \put(40,00){\makebox(0,0){\isa{group}}}
- \put(20,55){\vector(0,-1){10}}
- \put(15,35){\vector(-1,-1){10}}
- \put(05,15){\vector(3,-1){30}}
- \end{picture}
- \caption{Subclass relationship of monoids and groups:
- before and after establishing the relationship
- \isa{group\ {\isasymsubseteq}\ monoid}; transitive edges left out.}
- \label{fig:subclass}
- \end{center}
- \end{figure}
-7
- For illustration, a derived definition
- in \isa{group} which uses \isa{pow{\isacharunderscore}nat}:%
-\end{isamarkuptext}%
-\isamarkuptrue%
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-\isadelimquote
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-\endisadelimquote
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-\isatagquote
-\isacommand{definition}\isamarkupfalse%
-\ {\isacharparenleft}\isakeyword{in}\ group{\isacharparenright}\ pow{\isacharunderscore}int\ {\isacharcolon}{\isacharcolon}\ {\isachardoublequoteopen}int\ {\isasymRightarrow}\ {\isasymalpha}\ {\isasymRightarrow}\ {\isasymalpha}{\isachardoublequoteclose}\ \isakeyword{where}\isanewline
-\ \ {\isachardoublequoteopen}pow{\isacharunderscore}int\ k\ x\ {\isacharequal}\ {\isacharparenleft}if\ k\ {\isachargreater}{\isacharequal}\ {\isadigit{0}}\isanewline
-\ \ \ \ then\ pow{\isacharunderscore}nat\ {\isacharparenleft}nat\ k{\isacharparenright}\ x\isanewline
-\ \ \ \ else\ {\isacharparenleft}pow{\isacharunderscore}nat\ {\isacharparenleft}nat\ {\isacharparenleft}{\isacharminus}\ k{\isacharparenright}{\isacharparenright}\ x{\isacharparenright}{\isasymdiv}{\isacharparenright}{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
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-\isadelimquote
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-\endisadelimquote
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-\begin{isamarkuptext}%
-\noindent yields the global definition of
- \isa{{\isachardoublequote}pow{\isacharunderscore}int\ {\isasymColon}\ int\ {\isasymRightarrow}\ {\isasymalpha}{\isasymColon}group\ {\isasymRightarrow}\ {\isasymalpha}{\isasymColon}group{\isachardoublequote}}
- with the corresponding theorem \isa{pow{\isacharunderscore}int\ k\ x\ {\isacharequal}\ {\isacharparenleft}if\ {\isadigit{0}}\ {\isasymle}\ k\ then\ pow{\isacharunderscore}nat\ {\isacharparenleft}nat\ k{\isacharparenright}\ x\ else\ {\isacharparenleft}pow{\isacharunderscore}nat\ {\isacharparenleft}nat\ {\isacharparenleft}{\isacharminus}\ k{\isacharparenright}{\isacharparenright}\ x{\isacharparenright}{\isasymdiv}{\isacharparenright}}.%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isamarkupsubsection{A note on syntax%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-As a commodity, class context syntax allows to refer
- to local class operations and their global counterparts
- uniformly; type inference resolves ambiguities. For example:%
-\end{isamarkuptext}%
-\isamarkuptrue%
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-\isadelimquote
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-\endisadelimquote
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-\isatagquote
-\isacommand{context}\isamarkupfalse%
-\ semigroup\isanewline
-\isakeyword{begin}\isanewline
-\isanewline
-\isacommand{term}\isamarkupfalse%
-\ {\isachardoublequoteopen}x\ {\isasymotimes}\ y{\isachardoublequoteclose}\ %
-\isamarkupcmt{example 1%
-}
-\isanewline
-\isacommand{term}\isamarkupfalse%
-\ {\isachardoublequoteopen}{\isacharparenleft}x{\isasymColon}nat{\isacharparenright}\ {\isasymotimes}\ y{\isachardoublequoteclose}\ %
-\isamarkupcmt{example 2%
-}
-\isanewline
-\isanewline
-\isacommand{end}\isamarkupfalse%
-\isanewline
-\isanewline
-\isacommand{term}\isamarkupfalse%
-\ {\isachardoublequoteopen}x\ {\isasymotimes}\ y{\isachardoublequoteclose}\ %
-\isamarkupcmt{example 3%
-}
-%
-\endisatagquote
-{\isafoldquote}%
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-\isadelimquote
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-\endisadelimquote
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-\begin{isamarkuptext}%
-\noindent Here in example 1, the term refers to the local class operation
- \isa{mult\ {\isacharbrackleft}{\isasymalpha}{\isacharbrackright}}, whereas in example 2 the type constraint
- enforces the global class operation \isa{mult\ {\isacharbrackleft}nat{\isacharbrackright}}.
- In the global context in example 3, the reference is
- to the polymorphic global class operation \isa{mult\ {\isacharbrackleft}{\isacharquery}{\isasymalpha}\ {\isasymColon}\ semigroup{\isacharbrackright}}.%
-\end{isamarkuptext}%
-\isamarkuptrue%
-%
-\isamarkupsection{Further issues%
-}
-\isamarkuptrue%
-%
-\isamarkupsubsection{Type classes and code generation%
-}
-\isamarkuptrue%
-%
-\begin{isamarkuptext}%
-Turning back to the first motivation for type classes,
- namely overloading, it is obvious that overloading
- stemming from \hyperlink{command.class}{\mbox{\isa{\isacommand{class}}}} statements and
- \hyperlink{command.instantiation}{\mbox{\isa{\isacommand{instantiation}}}}
- targets naturally maps to Haskell type classes.
- The code generator framework \cite{isabelle-codegen}
- takes this into account. Concerning target languages
- lacking type classes (e.g.~SML), type classes
- are implemented by explicit dictionary construction.
- As example, let's go back to the power function:%
-\end{isamarkuptext}%
-\isamarkuptrue%
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-\isadelimquote
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-\endisadelimquote
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-\isatagquote
-\isacommand{definition}\isamarkupfalse%
-\ example\ {\isacharcolon}{\isacharcolon}\ int\ \isakeyword{where}\isanewline
-\ \ {\isachardoublequoteopen}example\ {\isacharequal}\ pow{\isacharunderscore}int\ {\isadigit{1}}{\isadigit{0}}\ {\isacharparenleft}{\isacharminus}{\isadigit{2}}{\isacharparenright}{\isachardoublequoteclose}%
-\endisatagquote
-{\isafoldquote}%
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-\endisadelimquote
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-\begin{isamarkuptext}%
-\noindent This maps to Haskell as:%
-\end{isamarkuptext}%
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-\begin{isamarkuptext}%
-\isatypewriter%
-\noindent%
-\hspace*{0pt}module Example where {\char123}\\
-\hspace*{0pt}\\
-\hspace*{0pt}\\
-\hspace*{0pt}data Nat = Zero{\char95}nat | Suc Nat;\\
-\hspace*{0pt}\\
-\hspace*{0pt}nat{\char95}aux ::~Integer -> Nat -> Nat;\\
-\hspace*{0pt}nat{\char95}aux i n = (if i <= 0 then n else nat{\char95}aux (i - 1) (Suc n));\\
-\hspace*{0pt}\\
-\hspace*{0pt}nat ::~Integer -> Nat;\\
-\hspace*{0pt}nat i = nat{\char95}aux i Zero{\char95}nat;\\
-\hspace*{0pt}\\
-\hspace*{0pt}class Semigroup a where {\char123}\\
-\hspace*{0pt} ~mult ::~a -> a -> a;\\
-\hspace*{0pt}{\char125};\\
-\hspace*{0pt}\\
-\hspace*{0pt}class (Semigroup a) => Monoidl a where {\char123}\\
-\hspace*{0pt} ~neutral ::~a;\\
-\hspace*{0pt}{\char125};\\
-\hspace*{0pt}\\
-\hspace*{0pt}class (Monoidl a) => Monoid a where {\char123}\\
-\hspace*{0pt}{\char125};\\
-\hspace*{0pt}\\
-\hspace*{0pt}class (Monoid a) => Group a where {\char123}\\
-\hspace*{0pt} ~inverse ::~a -> a;\\
-\hspace*{0pt}{\char125};\\
-\hspace*{0pt}\\
-\hspace*{0pt}inverse{\char95}int ::~Integer -> Integer;\\
-\hspace*{0pt}inverse{\char95}int i = negate i;\\
-\hspace*{0pt}\\
-\hspace*{0pt}neutral{\char95}int ::~Integer;\\
-\hspace*{0pt}neutral{\char95}int = 0;\\
-\hspace*{0pt}\\
-\hspace*{0pt}mult{\char95}int ::~Integer -> Integer -> Integer;\\
-\hspace*{0pt}mult{\char95}int i j = i + j;\\
-\hspace*{0pt}\\
-\hspace*{0pt}instance Semigroup Integer where {\char123}\\
-\hspace*{0pt} ~mult = mult{\char95}int;\\
-\hspace*{0pt}{\char125};\\
-\hspace*{0pt}\\
-\hspace*{0pt}instance Monoidl Integer where {\char123}\\
-\hspace*{0pt} ~neutral = neutral{\char95}int;\\
-\hspace*{0pt}{\char125};\\
-\hspace*{0pt}\\
-\hspace*{0pt}instance Monoid Integer where {\char123}\\
-\hspace*{0pt}{\char125};\\
-\hspace*{0pt}\\
-\hspace*{0pt}instance Group Integer where {\char123}\\
-\hspace*{0pt} ~inverse = inverse{\char95}int;\\
-\hspace*{0pt}{\char125};\\
-\hspace*{0pt}\\
-\hspace*{0pt}pow{\char95}nat ::~forall a.~(Monoid a) => Nat -> a -> a;\\
-\hspace*{0pt}pow{\char95}nat Zero{\char95}nat x = neutral;\\
-\hspace*{0pt}pow{\char95}nat (Suc n) x = mult x (pow{\char95}nat n x);\\
-\hspace*{0pt}\\
-\hspace*{0pt}pow{\char95}int ::~forall a.~(Group a) => Integer -> a -> a;\\
-\hspace*{0pt}pow{\char95}int k x =\\
-\hspace*{0pt} ~(if 0 <= k then pow{\char95}nat (nat k) x\\
-\hspace*{0pt} ~~~else inverse (pow{\char95}nat (nat (negate k)) x));\\
-\hspace*{0pt}\\
-\hspace*{0pt}example ::~Integer;\\
-\hspace*{0pt}example = pow{\char95}int 10 (-2);\\
-\hspace*{0pt}\\
-\hspace*{0pt}{\char125}%
-\end{isamarkuptext}%
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-\begin{isamarkuptext}%
-\noindent The whole code in SML with explicit dictionary passing:%
-\end{isamarkuptext}%
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-\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 nat{\char95}aux i n =\\
-\hspace*{0pt} ~(if IntInf.<= (i,~(0 :~IntInf.int)) then n\\
-\hspace*{0pt} ~~~else nat{\char95}aux (IntInf.- (i,~(1 :~IntInf.int))) (Suc n));\\
-\hspace*{0pt}\\
-\hspace*{0pt}fun nat i = nat{\char95}aux i Zero{\char95}nat;\\
-\hspace*{0pt}\\
-\hspace*{0pt}type 'a semigroup = {\char123}mult :~'a -> 'a -> 'a{\char125};\\
-\hspace*{0pt}fun mult (A{\char95}:'a semigroup) = {\char35}mult A{\char95};\\
-\hspace*{0pt}\\
-\hspace*{0pt}type 'a monoidl =\\
-\hspace*{0pt} ~{\char123}Classes{\char95}{\char95}semigroup{\char95}monoidl :~'a semigroup,~neutral :~'a{\char125};\\
-\hspace*{0pt}fun semigroup{\char95}monoidl (A{\char95}:'a monoidl) = {\char35}Classes{\char95}{\char95}semigroup{\char95}monoidl A{\char95};\\
-\hspace*{0pt}fun neutral (A{\char95}:'a monoidl) = {\char35}neutral A{\char95};\\
-\hspace*{0pt}\\
-\hspace*{0pt}type 'a monoid = {\char123}Classes{\char95}{\char95}monoidl{\char95}monoid :~'a monoidl{\char125};\\
-\hspace*{0pt}fun monoidl{\char95}monoid (A{\char95}:'a monoid) = {\char35}Classes{\char95}{\char95}monoidl{\char95}monoid A{\char95};\\
-\hspace*{0pt}\\
-\hspace*{0pt}type 'a group = {\char123}Classes{\char95}{\char95}monoid{\char95}group :~'a monoid,~inverse :~'a -> 'a{\char125};\\
-\hspace*{0pt}fun monoid{\char95}group (A{\char95}:'a group) = {\char35}Classes{\char95}{\char95}monoid{\char95}group A{\char95};\\
-\hspace*{0pt}fun inverse (A{\char95}:'a group) = {\char35}inverse A{\char95};\\
-\hspace*{0pt}\\
-\hspace*{0pt}fun inverse{\char95}int i = IntInf.{\char126}~i;\\
-\hspace*{0pt}\\
-\hspace*{0pt}val neutral{\char95}int :~IntInf.int = (0 :~IntInf.int)\\
-\hspace*{0pt}\\
-\hspace*{0pt}fun mult{\char95}int i j = IntInf.+ (i,~j);\\
-\hspace*{0pt}\\
-\hspace*{0pt}val semigroup{\char95}int = {\char123}mult = mult{\char95}int{\char125}~:~IntInf.int semigroup;\\
-\hspace*{0pt}\\
-\hspace*{0pt}val monoidl{\char95}int =\\
-\hspace*{0pt} ~{\char123}Classes{\char95}{\char95}semigroup{\char95}monoidl = semigroup{\char95}int,~neutral = neutral{\char95}int{\char125}~:\\
-\hspace*{0pt} ~IntInf.int monoidl;\\
-\hspace*{0pt}\\
-\hspace*{0pt}val monoid{\char95}int = {\char123}Classes{\char95}{\char95}monoidl{\char95}monoid = monoidl{\char95}int{\char125}~:\\
-\hspace*{0pt} ~IntInf.int monoid;\\
-\hspace*{0pt}\\
-\hspace*{0pt}val group{\char95}int =\\
-\hspace*{0pt} ~{\char123}Classes{\char95}{\char95}monoid{\char95}group = monoid{\char95}int,~inverse = inverse{\char95}int{\char125}~:\\
-\hspace*{0pt} ~IntInf.int group;\\
-\hspace*{0pt}\\
-\hspace*{0pt}fun pow{\char95}nat A{\char95}~Zero{\char95}nat x = neutral (monoidl{\char95}monoid A{\char95})\\
-\hspace*{0pt} ~| pow{\char95}nat A{\char95}~(Suc n) x =\\
-\hspace*{0pt} ~~~mult ((semigroup{\char95}monoidl o monoidl{\char95}monoid) A{\char95}) x (pow{\char95}nat A{\char95}~n x);\\
-\hspace*{0pt}\\
-\hspace*{0pt}fun pow{\char95}int A{\char95}~k x =\\
-\hspace*{0pt} ~(if IntInf.<= ((0 :~IntInf.int),~k)\\
-\hspace*{0pt} ~~~then pow{\char95}nat (monoid{\char95}group A{\char95}) (nat k) x\\
-\hspace*{0pt} ~~~else inverse A{\char95}~(pow{\char95}nat (monoid{\char95}group A{\char95}) (nat (IntInf.{\char126}~k)) x));\\
-\hspace*{0pt}\\
-\hspace*{0pt}val example :~IntInf.int =\\
-\hspace*{0pt} ~pow{\char95}int group{\char95}int (10 :~IntInf.int) ({\char126}2 :~IntInf.int)\\
-\hspace*{0pt}\\
-\hspace*{0pt}end;~(*struct Example*)%
-\end{isamarkuptext}%
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-\isamarkupsubsection{Inspecting the type class universe%
-}
-\isamarkuptrue%
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-\begin{isamarkuptext}%
-To facilitate orientation in complex subclass structures,
- two diagnostics commands are provided:
-
- \begin{description}
-
- \item[\hyperlink{command.print-classes}{\mbox{\isa{\isacommand{print{\isacharunderscore}classes}}}}] print a list of all classes
- together with associated operations etc.
-
- \item[\hyperlink{command.class-deps}{\mbox{\isa{\isacommand{class{\isacharunderscore}deps}}}}] visualizes the subclass relation
- between all classes as a Hasse diagram.
-
- \end{description}%
-\end{isamarkuptext}%
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-\end{isabellebody}%
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