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 \chapter{Isar document syntax}

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 FIXME important note: inner versus outer syntax

 \section{Lexical matters}

 \section{Common syntax entities}

 The Isar proof and theory language syntax has been carefully designed with

 orthogonality in mind.  Subsequently, we introduce several basic syntactic

 entities, such as names, terms, theorem specifications, which have been

 factored out of the actual Isar language elements described later.

 Some of the basic syntactic entities introduced below act much like tokens

 rather than nonterminals, in particular for error messages are concerned.

 E.g.\ syntax elements such as $\CONSTS$ referring to \railqtoken{name} or

 \railqtoken{type} would really report a missing \railqtoken{name} or

 \railqtoken{type} rather than any of its constituent primitive tokens

 (\railtoken{ident}, \railtoken{string} etc.).

 \subsection{Names}

 Entity \railqtoken{name} usually refers to any name of types, constants,

 theorems, etc.\ to be \emph{declared} or \emph{defined} (so qualified

 identifiers are excluded).  Quoted strings provide an escape for

 non-identifier names or those ruled out by outer syntax keywords (e.g.\ 

 \verb|"let"|).  Already existing objects are usually referenced by

 \railqtoken{nameref}.

 \indexoutertoken{name}\indexoutertoken{nameref}

 \begin{rail}

   name : ident | symident | string

   ;

   nameref : name | longident

   ;

 \end{rail}

 \subsection{Comments}

 Large chunks of plain \railqtoken{text} are usually given \railtoken{verbatim},

 i.e.\ enclosed in \verb|{*|\dots\verb|*}|.  For convenience, any of the

 smaller text entities (\railtoken{ident}, \railtoken{string} etc.)  are

 admitted as well.  Almost any of the Isar commands may be annotated by a

 marginal \railnonterm{comment}: \texttt{--} \railqtoken{text}.  Note that this

 kind of comment is actually part of the language, while source level comments

 \verb|(*|\dots\verb|*)| are already stripped at the lexical level.  A few

 commands such as $\PROOFNAME$ admit additional markup with a ``level of

 interest'', currently only \texttt{\%} for ``boring, don't read this''.

 \indexoutertoken{text}\indexouternonterm{comment}\indexouternonterm{interest}

 \begin{rail}

   text : verbatim | nameref

   ;

   comment : '--' text

   ;

   interest : '\%'

   ;

 \end{rail}

 \subsection{Sorts and arities}

 The syntax of sorts and arities is given directly at the outer level.  Note

 that this in contrast to that types and terms (see below).  Only few commands

 ever refer to sorts or arities explicitly.

 \indexouternonterm{sort}\indexouternonterm{arity}\indexouternonterm{simplearity}

 \begin{rail}

   sort : nameref | lbrace (nameref * ',') rbrace

   ;

   arity : ( () | '(' (sort + ',') ')' ) sort

   ;

   simplearity : ( () | '(' (sort + ',') ')' ) nameref

   ;

 \end{rail}

 \subsection{Types and terms}

 The actual inner Isabelle syntax, i.e.\ that of types and terms, is far too

 flexible in order to be modeled explicitly at the outer theory level.

 Basically, any such entity would have to be quoted at the outer level to turn

 it into a single token, with the actual parsing deferred to some functions

 that read and type-check terms etc.\ (note that \railqtoken{prop}s will be

 handled differently from plain \railqtoken{term}s here).  For convenience, the

 quotes may be omitted for any \emph{atomic} term or type (e.g.\ a single

 variable).

 \indexoutertoken{type}\indexoutertoken{term}\indexoutertoken{prop}

 \begin{rail}

   type : nameref | typefree | typevar

   ;

   term : nameref | var | textvar | nat

   ;

   prop : term

   ;

 \end{rail}

 Type definitions etc.\ usually refer to \railnonterm{typespec} on the

 left-hand side.  This models basic type constructor application at the outer

 syntax level.  Note that only plain postfix notation is available here, but no

 infixes.

 \indexouternonterm{typespec}

 \begin{rail}

   typespec : (() | typefree | '(' ( typefree + ',' ) ')') name

   ;

 \end{rail}

 \subsection{Term patterns}

 Statements like $\SHOWNAME$ involve propositions, some others like $\DEFNAME$

 plain terms.  Any of these usually admit automatic binding of schematic text

 variables by giving (optional) patterns $\IS{p@1 \dots p@n}$.  For

 \railqtoken{prop}s the $\CONCLNAME$ part refers to the conclusion only, in case

 actual rules are involved, rather than atomic propositions.

 \indexouternonterm{termpat}\indexouternonterm{proppat}

 \begin{rail}

   termpat : '(' (term + 'is' ) ')'

   ;

   proppat : '(' (() | (prop + 'is' )) (() | 'concl' (prop + 'is' )) ')'

   ;

 \end{rail}

 \subsection{Mixfix annotations}

 Mixfix annotations specify concrete \emph{inner} syntax of Isabelle types and

 terms.  Some commands such as $\TYPES$ admit infixes only, while $\CONSTS$

 etc.\ support the full range of general mixfixes and binders.

 \indexouternonterm{infix}\indexouternonterm{mixfix}

 \begin{rail}

   infix : '(' ('infixl' | 'infixr') (() | string) nat ')'

   ;

   mixfix : infix | string (() | '[' (nat + ',') ']') (() | nat) |

   'binder' string (() | '[' (nat + ',') ']') nat

   ;

 \end{rail}

 \subsection{Attributes and theorems}\label{sec:syn-att}

 Attributes (and proof methods, see \S\ref{sec:syn-meth}) have their own

 ``semi-inner'' syntax, which does not have to be atomic at the outer level

 unlike that of types and terms.  Instead, the attribute argument

 specifications may be any sequence of atomic entities (identifiers, strings

 etc.), or properly bracketed argument lists.  Below \railqtoken{atom} refers to

 any atomic entity (\railtoken{ident}, \railtoken{longident},

 \railtoken{symident} etc.), including keywords that conform to

 \railtoken{symident}, but do not coincide with actual command names.

 \indexoutertoken{atom}\indexouternonterm{args}\indexouternonterm{attributes}

 \begin{rail}

   atom : nameref | typefree | typevar | var | textvar | nat

   ;

   arg : atom | '(' args ')' | '[' args ']' | lbrace args rbrace

   ;

   args : arg *

   ;

   attributes : '[' (nameref args * ',') ']'

   ;

 \end{rail}

 Theorem specifications come in three flavors: \railnonterm{thmdecl} usually

 refers to the result of an assumption or goal statement (e.g.\ $\SHOWNAME$),

 \railnonterm{thmdef} collects lists of existing theorems (as in $\NOTENAME$),

 \railnonterm{thmrefs} refers to any list of existing theorems (e.g.\ occurring

 as proof method arguments).  Any of these may include lists of attributes,

 which are applied to the preceding theorem or list of theorems.

 \indexouternonterm{thmdecl}\indexouternonterm{thmdef}\indexouternonterm{thmrefs}

 \begin{rail}

   thmname : name attributes | name | attributes

   ;

   thmdecl : thmname ':'

   ;

   thmdef : thmname '='

   ;

   thmrefs : nameref (() | attributes) +

   ;

 \end{rail}

 \subsection{Proof methods}\label{sec:syn-meth}

 Proof methods are either basic ones, or expressions composed of methods via

 ``\texttt{,}'' (sequential composition), ``\texttt{|}'' (alternatives),

 ``\texttt{?}'' (try), ``\texttt{*}'' (repeat, ${} \ge 0$ times),

 ``\texttt{+}'' (repeat, ${} > 0$ times).  In practice, proof methods are very

 often just a comma separated list of \railqtoken{nameref}~\railnonterm{args}

 specifications.  Thus the syntax is similar to that of attributes, with plain

 parentheses instead of square brackets (see also \S\ref{sec:syn-att}).  Note

 that parentheses may be dropped for single method specifications without

 arguments.

 \indexouternonterm{method}

 \begin{rail}

   method : (nameref | '(' methods ')') (() | '?' | '*' | '+')

   ;

   methods : (nameref args | method) + (',' | '|')

   ;

 \end{rail}

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