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diff --git a/doc/refman/RefMan-ext.tex b/doc/refman/RefMan-ext.tex deleted file mode 100644 index c0e578fe..00000000 --- a/doc/refman/RefMan-ext.tex +++ /dev/null @@ -1,1756 +0,0 @@ -\chapter[Extensions of \Gallina{}]{Extensions of \Gallina{}\label{Gallina-extension}\index{Gallina}} - -{\gallina} is the kernel language of {\Coq}. We describe here extensions of -the Gallina's syntax. - -\section{Record types -\comindex{Record} -\label{Record}} - -The \verb+Record+ construction is a macro allowing the definition of -records as is done in many programming languages. Its syntax is -described on Figure~\ref{record-syntax}. In fact, the \verb+Record+ -macro is more general than the usual record types, since it allows -also for ``manifest'' expressions. In this sense, the \verb+Record+ -construction allows to define ``signatures''. - -\begin{figure}[h] -\begin{centerframe} -\begin{tabular}{lcl} -{\sentence} & ++= & {\record}\\ - & & \\ -{\record} & ::= & - {\tt Record} {\ident} \zeroone{\binders} \zeroone{{\tt :} {\sort}} \verb.:=. \\ -&& ~~~~\zeroone{\ident} - \verb!{! \zeroone{\nelist{\field}{;}} \verb!}! \verb:.:\\ - & & \\ -{\field} & ::= & {\name} \zeroone{\binders} : {\type} [ {\tt where} {\it notation} ] \\ - & $|$ & {\name} \zeroone{\binders} {\typecstr} := {\term} -\end{tabular} -\end{centerframe} -\caption{Syntax for the definition of {\tt Record}} -\label{record-syntax} -\end{figure} - -\noindent In the expression - -\smallskip -{\tt Record} {\ident} {\params} \texttt{:} - {\sort} := {\ident$_0$} \verb+{+ - {\ident$_1$} \binders$_1$ \texttt{:} {\term$_1$}; - \dots - {\ident$_n$} \binders$_n$ \texttt{:} {\term$_n$} \verb+}+. -\smallskip - -\noindent the identifier {\ident} is the name of the defined record -and {\sort} is its type. The identifier {\ident$_0$} is the name of -its constructor. If {\ident$_0$} is omitted, the default name {\tt -Build\_{\ident}} is used. If {\sort} is omitted, the default sort is ``{\Type}''. -The identifiers {\ident$_1$}, .., -{\ident$_n$} are the names of fields and {\tt forall} \binders$_1${\tt ,} {\term$_1$}, ..., {\tt forall} \binders$_n${\tt ,} {\term$_n$} -their respective types. Remark that the type of {\ident$_i$} may -depend on the previous {\ident$_j$} (for $j<i$). Thus the order of the -fields is important. Finally, {\params} are the parameters of the -record. - -More generally, a record may have explicitly defined (a.k.a. -manifest) fields. For instance, {\tt Record} {\ident} {\tt [} -{\params} {\tt ]} \texttt{:} {\sort} := \verb+{+ {\ident$_1$} -\texttt{:} {\type$_1$} \verb+;+ {\ident$_2$} \texttt{:=} {\term$_2$} -\verb+;+ {\ident$_3$} \texttt{:} {\type$_3$} \verb+}+ in which case -the correctness of {\type$_3$} may rely on the instance {\term$_2$} of -{\ident$_2$} and {\term$_2$} in turn may depend on {\ident$_1$}. - - -\Example -The set of rational numbers may be defined as: -\begin{coq_eval} -Reset Initial. -\end{coq_eval} -\begin{coq_example} -Record Rat : Set := mkRat - {sign : bool; - top : nat; - bottom : nat; - Rat_bottom_cond : 0 <> bottom; - Rat_irred_cond : - forall x y z:nat, (x * y) = top /\ (x * z) = bottom -> x = 1}. -\end{coq_example} - -Remark here that the field -\verb+Rat_cond+ depends on the field \verb+bottom+. - -%Let us now see the work done by the {\tt Record} macro. -%First the macro generates an inductive definition -%with just one constructor: -% -%\medskip -%\noindent -%{\tt Inductive {\ident} \zeroone{\binders} : {\sort} := \\ -%\mbox{}\hspace{0.4cm} {\ident$_0$} : forall ({\ident$_1$}:{\term$_1$}) .. -%({\ident$_n$}:{\term$_n$}), {\ident} {\rm\sl params}.} -%\medskip - -Let us now see the work done by the {\tt Record} macro. First the -macro generates an inductive definition with just one constructor: -\begin{quote} -{\tt Inductive {\ident} {\params} :{\sort} :=} \\ -\qquad {\tt - {\ident$_0$} ({\ident$_1$}:{\term$_1$}) .. ({\ident$_n$}:{\term$_n$}).} -\end{quote} -To build an object of type {\ident}, one should provide the -constructor {\ident$_0$} with $n$ terms filling the fields of -the record. - -As an example, let us define the rational $1/2$: -\begin{coq_example*} -Require Import Arith. -Theorem one_two_irred : - forall x y z:nat, x * y = 1 /\ x * z = 2 -> x = 1. -\end{coq_example*} -\begin{coq_eval} -Lemma mult_m_n_eq_m_1 : forall m n:nat, m * n = 1 -> m = 1. -destruct m; trivial. -intros; apply f_equal with (f := S). -destruct m; trivial. -destruct n; simpl in H. - rewrite <- mult_n_O in H. - discriminate. - rewrite <- plus_n_Sm in H. - discriminate. -Qed. - -intros x y z [H1 H2]. - apply mult_m_n_eq_m_1 with (n := y); trivial. -\end{coq_eval} -\ldots -\begin{coq_example*} -Qed. -\end{coq_example*} -\begin{coq_example} -Definition half := mkRat true 1 2 (O_S 1) one_two_irred. -\end{coq_example} -\begin{coq_example} -Check half. -\end{coq_example} - -The macro generates also, when it is possible, the projection -functions for destructuring an object of type {\ident}. These -projection functions have the same name that the corresponding -fields. If a field is named ``\verb=_='' then no projection is built -for it. In our example: - -\begin{coq_example} -Eval compute in half.(top). -Eval compute in half.(bottom). -Eval compute in half.(Rat_bottom_cond). -\end{coq_example} -\begin{coq_eval} -Reset Initial. -\end{coq_eval} - -\begin{Warnings} -\item {\tt Warning: {\ident$_i$} cannot be defined.} - - It can happen that the definition of a projection is impossible. - This message is followed by an explanation of this impossibility. - There may be three reasons: - \begin{enumerate} - \item The name {\ident$_i$} already exists in the environment (see - Section~\ref{Axiom}). - \item The body of {\ident$_i$} uses an incorrect elimination for - {\ident} (see Sections~\ref{Fixpoint} and~\ref{Caseexpr}). - \item The type of the projections {\ident$_i$} depends on previous - projections which themselves could not be defined. - \end{enumerate} -\end{Warnings} - -\begin{ErrMsgs} - -\item \errindex{A record cannot be recursive} - - The record name {\ident} appears in the type of its fields. - -\item During the definition of the one-constructor inductive - definition, all the errors of inductive definitions, as described in - Section~\ref{gal_Inductive_Definitions}, may also occur. - -\end{ErrMsgs} - -\SeeAlso Coercions and records in Section~\ref{Coercions-and-records} -of the chapter devoted to coercions. - -\Rem {\tt Structure} is a synonym of the keyword {\tt Record}. - -\Rem Creation of an object of record type can be done by calling {\ident$_0$} -and passing arguments in the correct order. - -\begin{coq_example} -Record point := { x : nat; y : nat }. -Definition a := Build_point 5 3. -\end{coq_example} - -The following syntax allows to create objects by using named fields. The -fields do not have to be in any particular order, nor do they have to be all -present if the missing ones can be inferred or prompted for (see -Section~\ref{Program}). - -\begin{coq_example} -Definition b := {| x := 5; y := 3 |}. -Definition c := {| y := 3; x := 5 |}. -\end{coq_example} - -This syntax can also be used for pattern matching. - -\begin{coq_example} -Eval compute in ( - match b with - | {| y := S n |} => n - | _ => 0 - end). -\end{coq_example} - -\begin{coq_eval} -Reset Initial. -\end{coq_eval} - -\Rem An experimental syntax for projections based on a dot notation is -available. The command to activate it is -\begin{quote} -{\tt Set Printing Projections.} -\end{quote} - -\begin{figure}[t] -\begin{centerframe} -\begin{tabular}{lcl} -{\term} & ++= & {\term} {\tt .(} {\qualid} {\tt )}\\ - & $|$ & {\term} {\tt .(} {\qualid} \nelist{\termarg}{} {\tt )}\\ - & $|$ & {\term} {\tt .(} {@}{\qualid} \nelist{\term}{} {\tt )} -\end{tabular} -\end{centerframe} -\caption{Syntax of \texttt{Record} projections} -\label{fig:projsyntax} -\end{figure} - -The corresponding grammar rules are given Figure~\ref{fig:projsyntax}. -When {\qualid} denotes a projection, the syntax {\tt - {\term}.({\qualid})} is equivalent to {\qualid~\term}, the syntax -{\tt {\term}.({\qualid}~{\termarg}$_1$~ \ldots~ {\termarg}$_n$)} to -{\qualid~{\termarg}$_1$ \ldots {\termarg}$_n$~\term}, and the syntax -{\tt {\term}.(@{\qualid}~{\term}$_1$~\ldots~{\term}$_n$)} to -{@\qualid~{\term}$_1$ \ldots {\term}$_n$~\term}. In each case, {\term} -is the object projected and the other arguments are the parameters of -the inductive type. - -To deactivate the printing of projections, use -{\tt Unset Printing Projections}. - - -\section{Variants and extensions of {\mbox{\tt match}} -\label{Extensions-of-match} -\index{match@{\tt match\ldots with\ldots end}}} - -\subsection{Multiple and nested pattern-matching -\index{ML-like patterns} -\label{Mult-match}} - -The basic version of \verb+match+ allows pattern-matching on simple -patterns. As an extension, multiple nested patterns or disjunction of -patterns are allowed, as in ML-like languages. - -The extension just acts as a macro that is expanded during parsing -into a sequence of {\tt match} on simple patterns. Especially, a -construction defined using the extended {\tt match} is generally -printed under its expanded form (see~\texttt{Set Printing Matching} in -section~\ref{SetPrintingMatching}). - -\SeeAlso Chapter~\ref{Mult-match-full}. - -\subsection{Pattern-matching on boolean values: the {\tt if} expression -\label{if-then-else} -\index{if@{\tt if ... then ... else}}} - -For inductive types with exactly two constructors and for -pattern-matchings expressions which do not depend on the arguments of -the constructors, it is possible to use a {\tt if ... then ... else} -notation. For instance, the definition - -\begin{coq_example} -Definition not (b:bool) := - match b with - | true => false - | false => true - end. -\end{coq_example} - -\noindent can be alternatively written - -\begin{coq_eval} -Reset not. -\end{coq_eval} -\begin{coq_example} -Definition not (b:bool) := if b then false else true. -\end{coq_example} - -More generally, for an inductive type with constructors {\tt C$_1$} -and {\tt C$_2$}, we have the following equivalence - -\smallskip - -{\tt if {\term} \zeroone{\ifitem} then {\term}$_1$ else {\term}$_2$} $\equiv$ -\begin{tabular}[c]{l} -{\tt match {\term} \zeroone{\ifitem} with}\\ -{\tt \verb!|! C$_1$ \_ {\ldots} \_ \verb!=>! {\term}$_1$} \\ -{\tt \verb!|! C$_2$ \_ {\ldots} \_ \verb!=>! {\term}$_2$} \\ -{\tt end} -\end{tabular} - -Here is an example. - -\begin{coq_example} -Check (fun x (H:{x=0}+{x<>0}) => - match H with - | left _ => true - | right _ => false - end). -\end{coq_example} - -Notice that the printing uses the {\tt if} syntax because {\tt sumbool} is -declared as such (see Section~\ref{printing-options}). - -\subsection{Irrefutable patterns: the destructuring {\tt let} variants -\index{let in@{\tt let ... in}} -\label{Letin}} - -Pattern-matching on terms inhabiting inductive type having only one -constructor can be alternatively written using {\tt let ... in ...} -constructions. There are two variants of them. - -\subsubsection{First destructuring {\tt let} syntax} -The expression {\tt let -(}~{\ident$_1$},\ldots,{\ident$_n$}~{\tt ) :=}~{\term$_0$}~{\tt -in}~{\term$_1$} performs case analysis on a {\term$_0$} which must be in -an inductive type with one constructor having itself $n$ arguments. Variables -{\ident$_1$}\ldots{\ident$_n$} are bound to the $n$ arguments of the -constructor in expression {\term$_1$}. For instance, the definition - -\begin{coq_example} -Definition fst (A B:Set) (H:A * B) := match H with - | pair x y => x - end. -\end{coq_example} - -can be alternatively written - -\begin{coq_eval} -Reset fst. -\end{coq_eval} -\begin{coq_example} -Definition fst (A B:Set) (p:A * B) := let (x, _) := p in x. -\end{coq_example} -Notice that reduction is different from regular {\tt let ... in ...} -construction since it happens only if {\term$_0$} is in constructor -form. Otherwise, the reduction is blocked. - -The pretty-printing of a definition by matching on a -irrefutable pattern can either be done using {\tt match} or the {\tt -let} construction (see Section~\ref{printing-options}). - -If {\term} inhabits an inductive type with one constructor {\tt C}, -we have an equivalence between - -{\tt let ({\ident}$_1$,\ldots,{\ident}$_n$) \zeroone{\ifitem} := {\term} in {\term}'} - -\noindent and - -{\tt match {\term} \zeroone{\ifitem} with C {\ident}$_1$ {\ldots} {\ident}$_n$ \verb!=>! {\term}' end} - - -\subsubsection{Second destructuring {\tt let} syntax\index{let '... in}} - -Another destructuring {\tt let} syntax is available for inductive types with -one constructor by giving an arbitrary pattern instead of just a tuple -for all the arguments. For example, the preceding example can be written: -\begin{coq_eval} -Reset fst. -\end{coq_eval} -\begin{coq_example} -Definition fst (A B:Set) (p:A*B) := let 'pair x _ := p in x. -\end{coq_example} - -This is useful to match deeper inside tuples and also to use notations -for the pattern, as the syntax {\tt let 'p := t in b} allows arbitrary -patterns to do the deconstruction. For example: - -\begin{coq_example} -Definition deep_tuple (A:Set) (x:(A*A)*(A*A)) : A*A*A*A := - let '((a,b), (c, d)) := x in (a,b,c,d). -Notation " x 'with' p " := (exist _ x p) (at level 20). -Definition proj1_sig' (A:Set) (P:A->Prop) (t:{ x:A | P x }) : A := - let 'x with p := t in x. -\end{coq_example} - -When printing definitions which are written using this construct it -takes precedence over {\tt let} printing directives for the datatype -under consideration (see Section~\ref{printing-options}). - -\subsection{Controlling pretty-printing of {\tt match} expressions -\label{printing-options}} - -The following commands give some control over the pretty-printing of -{\tt match} expressions. - -\subsubsection{Printing nested patterns -\label{SetPrintingMatching} -\comindex{Set Printing Matching} -\comindex{Unset Printing Matching} -\comindex{Test Printing Matching}} - -The Calculus of Inductive Constructions knows pattern-matching only -over simple patterns. It is however convenient to re-factorize nested -pattern-matching into a single pattern-matching over a nested pattern. -{\Coq}'s printer try to do such limited re-factorization. - -\begin{quote} -{\tt Set Printing Matching.} -\end{quote} -This tells {\Coq} to try to use nested patterns. This is the default -behavior. - -\begin{quote} -{\tt Unset Printing Matching.} -\end{quote} -This tells {\Coq} to print only simple pattern-matching problems in -the same way as the {\Coq} kernel handles them. - -\begin{quote} -{\tt Test Printing Matching.} -\end{quote} -This tells if the printing matching mode is on or off. The default is -on. - -\subsubsection{Printing of wildcard pattern -\comindex{Set Printing Wildcard} -\comindex{Unset Printing Wildcard} -\comindex{Test Printing Wildcard}} - -Some variables in a pattern may not occur in the right-hand side of -the pattern-matching clause. There are options to control the -display of these variables. - -\begin{quote} -{\tt Set Printing Wildcard.} -\end{quote} -The variables having no occurrences in the right-hand side of the -pattern-matching clause are just printed using the wildcard symbol -``{\tt \_}''. - -\begin{quote} -{\tt Unset Printing Wildcard.} -\end{quote} -The variables, even useless, are printed using their usual name. But some -non dependent variables have no name. These ones are still printed -using a ``{\tt \_}''. - -\begin{quote} -{\tt Test Printing Wildcard.} -\end{quote} -This tells if the wildcard printing mode is on or off. The default is -to print wildcard for useless variables. - -\subsubsection{Printing of the elimination predicate -\comindex{Set Printing Synth} -\comindex{Unset Printing Synth} -\comindex{Test Printing Synth}} - -In most of the cases, the type of the result of a matched term is -mechanically synthesizable. Especially, if the result type does not -depend of the matched term. - -\begin{quote} -{\tt Set Printing Synth.} -\end{quote} -The result type is not printed when {\Coq} knows that it can -re-synthesize it. - -\begin{quote} -{\tt Unset Printing Synth.} -\end{quote} -This forces the result type to be always printed. - -\begin{quote} -{\tt Test Printing Synth.} -\end{quote} -This tells if the non-printing of synthesizable types is on or off. -The default is to not print synthesizable types. - -\subsubsection{Printing matching on irrefutable pattern -\comindex{Add Printing Let {\ident}} -\comindex{Remove Printing Let {\ident}} -\comindex{Test Printing Let for {\ident}} -\comindex{Print Table Printing Let}} - -If an inductive type has just one constructor, -pattern-matching can be written using {\tt let} ... {\tt :=} -... {\tt in}~... - -\begin{quote} -{\tt Add Printing Let {\ident}.} -\end{quote} -This adds {\ident} to the list of inductive types for which -pattern-matching is written using a {\tt let} expression. - -\begin{quote} -{\tt Remove Printing Let {\ident}.} -\end{quote} -This removes {\ident} from this list. - -\begin{quote} -{\tt Test Printing Let for {\ident}.} -\end{quote} -This tells if {\ident} belongs to the list. - -\begin{quote} -{\tt Print Table Printing Let.} -\end{quote} -This prints the list of inductive types for which pattern-matching is -written using a {\tt let} expression. - -The list of inductive types for which pattern-matching is written -using a {\tt let} expression is managed synchronously. This means that -it is sensible to the command {\tt Reset}. - -\subsubsection{Printing matching on booleans -\comindex{Add Printing If {\ident}} -\comindex{Remove Printing If {\ident}} -\comindex{Test Printing If for {\ident}} -\comindex{Print Table Printing If}} - -If an inductive type is isomorphic to the boolean type, -pattern-matching can be written using {\tt if} ... {\tt then} ... {\tt - else} ... - -\begin{quote} -{\tt Add Printing If {\ident}.} -\end{quote} -This adds {\ident} to the list of inductive types for which -pattern-matching is written using an {\tt if} expression. - -\begin{quote} -{\tt Remove Printing If {\ident}.} -\end{quote} -This removes {\ident} from this list. - -\begin{quote} -{\tt Test Printing If for {\ident}.} -\end{quote} -This tells if {\ident} belongs to the list. - -\begin{quote} -{\tt Print Table Printing If.} -\end{quote} -This prints the list of inductive types for which pattern-matching is -written using an {\tt if} expression. - -The list of inductive types for which pattern-matching is written -using an {\tt if} expression is managed synchronously. This means that -it is sensible to the command {\tt Reset}. - -\subsubsection{Example} - -This example emphasizes what the printing options offer. - -\begin{coq_example} -Test Printing Let for prod. -Print fst. -Remove Printing Let prod. -Unset Printing Synth. -Unset Printing Wildcard. -Print fst. -\end{coq_example} - -% \subsection{Still not dead old notations} - -% The following variant of {\tt match} is inherited from older version -% of {\Coq}. - -% \medskip -% \begin{tabular}{lcl} -% {\term} & ::= & {\annotation} {\tt Match} {\term} {\tt with} {\terms} {\tt end}\\ -% \end{tabular} -% \medskip - -% This syntax is a macro generating a combination of {\tt match} with {\tt -% Fix} implementing a combinator for primitive recursion equivalent to -% the {\tt Match} construction of \Coq\ V5.8. It is provided only for -% sake of compatibility with \Coq\ V5.8. It is recommended to avoid it. -% (see Section~\ref{Matchexpr}). - -% There is also a notation \texttt{Case} that is the -% ancestor of \texttt{match}. Again, it is still in the code for -% compatibility with old versions but the user should not use it. - -% Explained in RefMan-gal.tex -%% \section{Forced type} - -%% In some cases, one may wish to assign a particular type to a term. The -%% syntax to force the type of a term is the following: - -%% \medskip -%% \begin{tabular}{lcl} -%% {\term} & ++= & {\term} {\tt :} {\term}\\ -%% \end{tabular} -%% \medskip - -%% It forces the first term to be of type the second term. The -%% type must be compatible with -%% the term. More precisely it must be either a type convertible to -%% the automatically inferred type (see Chapter~\ref{Cic}) or a type -%% coercible to it, (see \ref{Coercions}). When the type of a -%% whole expression is forced, it is usually not necessary to give the types of -%% the variables involved in the term. - -%% Example: - -%% \begin{coq_example} -%% Definition ID := forall X:Set, X -> X. -%% Definition id := (fun X x => x):ID. -%% Check id. -%% \end{coq_example} - -\section{Advanced recursive functions} - -The \emph{experimental} command -\begin{center} - \texttt{Function {\ident} {\binder$_1$}\ldots{\binder$_n$} - \{decrease\_annot\} : type$_0$ := \term$_0$} - \comindex{Function} - \label{Function} -\end{center} -can be seen as a generalization of {\tt Fixpoint}. It is actually a -wrapper for several ways of defining a function \emph{and other useful - related objects}, namely: an induction principle that reflects the -recursive structure of the function (see \ref{FunInduction}), and its -fixpoint equality. The meaning of this -declaration is to define a function {\it ident}, similarly to {\tt - Fixpoint}. Like in {\tt Fixpoint}, the decreasing argument must be -given (unless the function is not recursive), but it must not -necessary be \emph{structurally} decreasing. The point of the {\tt - \{\}} annotation is to name the decreasing argument \emph{and} to -describe which kind of decreasing criteria must be used to ensure -termination of recursive calls. - -The {\tt Function} construction enjoys also the {\tt with} extension -to define mutually recursive definitions. However, this feature does -not work for non structural recursive functions. % VRAI?? - -See the documentation of {\tt functional induction} -(see Section~\ref{FunInduction}) and {\tt Functional Scheme} -(see Section~\ref{FunScheme} and \ref{FunScheme-examples}) for how to use the -induction principle to easily reason about the function. - -\noindent {\bf Remark: } To obtain the right principle, it is better -to put rigid parameters of the function as first arguments. For -example it is better to define plus like this: - -\begin{coq_example*} -Function plus (m n : nat) {struct n} : nat := - match n with - | 0 => m - | S p => S (plus m p) - end. -\end{coq_example*} -\noindent than like this: -\begin{coq_eval} -Reset plus. -\end{coq_eval} -\begin{coq_example*} -Function plus (n m : nat) {struct n} : nat := - match n with - | 0 => m - | S p => S (plus p m) - end. -\end{coq_example*} - -\paragraph[Limitations]{Limitations\label{sec:Function-limitations}} -\term$_0$ must be build as a \emph{pure pattern-matching tree} -(\texttt{match...with}) with applications only \emph{at the end} of -each branch. For now dependent cases are not treated. - - - -\begin{ErrMsgs} -\item \errindex{The recursive argument must be specified} -\item \errindex{No argument name \ident} -\item \errindex{Cannot use mutual definition with well-founded - recursion or measure} - -\item \errindex{Cannot define graph for \ident\dots} (warning) - - The generation of the graph relation \texttt{(R\_\ident)} used to - compute the induction scheme of \ident\ raised a typing error. Only - the ident is defined, the induction scheme will not be generated. - - This error happens generally when: - - \begin{itemize} - \item the definition uses pattern matching on dependent types, which - \texttt{Function} cannot deal with yet. - \item the definition is not a \emph{pattern-matching tree} as - explained above. - \end{itemize} - -\item \errindex{Cannot define principle(s) for \ident\dots} (warning) - - The generation of the graph relation \texttt{(R\_\ident)} succeeded - but the induction principle could not be built. Only the ident is - defined. Please report. - -\item \errindex{Cannot build functional inversion principle} (warning) - - \texttt{functional inversion} will not be available for the - function. -\end{ErrMsgs} - - -\SeeAlso{\ref{FunScheme}, \ref{FunScheme-examples}, \ref{FunInduction}} - -Depending on the {\tt \{$\ldots$\}} annotation, different definition -mechanisms are used by {\tt Function}. More precise description -given below. - -\begin{Variants} -\item \texttt{ Function {\ident} {\binder$_1$}\ldots{\binder$_n$} - : type$_0$ := \term$_0$} - - Defines the not recursive function \ident\ as if declared with - \texttt{Definition}. Moreover the following are defined: - - \begin{itemize} - \item {\tt\ident\_rect}, {\tt\ident\_rec} and {\tt\ident\_ind}, - which reflect the pattern matching structure of \term$_0$ (see the - documentation of {\tt Inductive} \ref{Inductive}); - \item The inductive \texttt{R\_\ident} corresponding to the graph of - \ident\ (silently); - \item \texttt{\ident\_complete} and \texttt{\ident\_correct} which are - inversion information linking the function and its graph. - \end{itemize} -\item \texttt{Function {\ident} {\binder$_1$}\ldots{\binder$_n$} - {\tt \{}{\tt struct} \ident$_0${\tt\}} : type$_0$ := \term$_0$} - - Defines the structural recursive function \ident\ as if declared - with \texttt{Fixpoint}. Moreover the following are defined: - - \begin{itemize} - \item The same objects as above; - \item The fixpoint equation of \ident: \texttt{\ident\_equation}. - \end{itemize} - -\item \texttt{Function {\ident} {\binder$_1$}\ldots{\binder$_n$} {\tt - \{}{\tt measure \term$_1$} \ident$_0${\tt\}} : type$_0$ := - \term$_0$} -\item \texttt{Function {\ident} {\binder$_1$}\ldots{\binder$_n$} - {\tt \{}{\tt wf \term$_1$} \ident$_0${\tt\}} : type$_0$ := \term$_0$} - -Defines a recursive function by well founded recursion. \textbf{The -module \texttt{Recdef} of the standard library must be loaded for this -feature}. The {\tt \{\}} annotation is mandatory and must be one of -the following: -\begin{itemize} -\item {\tt \{measure} \term$_1$ \ident$_0${\tt\}} with \ident$_0$ - being the decreasing argument and \term$_1$ being a function - from type of \ident$_0$ to \texttt{nat} for which value on the - decreasing argument decreases (for the {\tt lt} order on {\tt - nat}) at each recursive call of \term$_0$, parameters of the - function are bound in \term$_0$; -\item {\tt \{wf} \term$_1$ \ident$_0${\tt\}} with \ident$_0$ being - the decreasing argument and \term$_1$ an ordering relation on - the type of \ident$_0$ (i.e. of type T$_{\ident_0}$ - $\to$ T$_{\ident_0}$ $\to$ {\tt Prop}) for which - the decreasing argument decreases at each recursive call of - \term$_0$. The order must be well founded. parameters of the - function are bound in \term$_0$. -\end{itemize} - -Depending on the annotation, the user is left with some proof -obligations that will be used to define the function. These proofs -are: proofs that each recursive call is actually decreasing with -respect to the given criteria, and (if the criteria is \texttt{wf}) a -proof that the ordering relation is well founded. - -%Completer sur measure et wf - -Once proof obligations are discharged, the following objects are -defined: - -\begin{itemize} -\item The same objects as with the \texttt{struct}; -\item The lemma \texttt{\ident\_tcc} which collects all proof - obligations in one property; -\item The lemmas \texttt{\ident\_terminate} and \texttt{\ident\_F} - which is needed to be inlined during extraction of \ident. -\end{itemize} - - - -%Complete!! -The way this recursive function is defined is the subject of several -papers by Yves Bertot and Antonia Balaa on the one hand, and Gilles Barthe, -Julien Forest, David Pichardie, and Vlad Rusu on the other hand. - -%Exemples ok ici - -\bigskip - -\noindent {\bf Remark: } Proof obligations are presented as several -subgoals belonging to a Lemma {\ident}{\tt\_tcc}. % These subgoals are independent which means that in order to -% abort them you will have to abort each separately. - - - -%The decreasing argument cannot be dependent of another?? - -%Exemples faux ici -\end{Variants} - - -\section{Section mechanism -\index{Sections} -\label{Section}} - -The sectioning mechanism allows to organize a proof in structured -sections. Then local declarations become available (see -Section~\ref{Basic-definitions}). - -\subsection{\tt Section {\ident}\comindex{Section}} - -This command is used to open a section named {\ident}. - -%% Discontinued ? -%% \begin{Variants} -%% \comindex{Chapter} -%% \item{\tt Chapter {\ident}}\\ -%% Same as {\tt Section {\ident}} -%% \end{Variants} - -\subsection{\tt End {\ident} -\comindex{End}} - -This command closes the section named {\ident}. After closing of the -section, the local declarations (variables and local definitions) get -{\em discharged}, meaning that they stop being visible and that all -global objects defined in the section are generalized with respect to -the variables and local definitions they each depended on in the -section. - - -Here is an example : -\begin{coq_example} -Section s1. -Variables x y : nat. -Let y' := y. -Definition x' := S x. -Definition x'' := x' + y'. -Print x'. -End s1. -Print x'. -Print x''. -\end{coq_example} -Notice the difference between the value of {\tt x'} and {\tt x''} -inside section {\tt s1} and outside. - -\begin{ErrMsgs} -\item \errindex{This is not the last opened section} -\end{ErrMsgs} - -\begin{Remarks} -\item Most commands, like {\tt Hint}, {\tt Notation}, option management, ... -which appear inside a section are canceled when the -section is closed. -% see Section~\ref{LongNames} -%\item Usually all identifiers must be distinct. -%However, a name already used in a closed section (see \ref{Section}) -%can be reused. In this case, the old name is no longer accessible. - -% Obsolète -%\item A module implicitly open a section. Be careful not to name a -%module with an identifier already used in the module (see \ref{compiled}). -\end{Remarks} - -\input{RefMan-mod.v} - -\section{Libraries and qualified names} - -\subsection{Names of libraries and files -\label{Libraries} -\index{Libraries} -\index{Physical paths} -\index{Logical paths}} - -\paragraph{Libraries} - -The theories developed in {\Coq} are stored in {\em library files} -which are hierarchically classified into {\em libraries} and {\em -sublibraries}. To express this hierarchy, library names are -represented by qualified identifiers {\qualid}, i.e. as list of -identifiers separated by dots (see Section~\ref{qualid}). For -instance, the library file {\tt Mult} of the standard {\Coq} library -{\tt Arith} has name {\tt Coq.Arith.Mult}. The identifier -that starts the name of a library is called a {\em library root}. -All library files of the standard library of {\Coq} have reserved root -{\tt Coq} but library file names based on other roots can be obtained -by using {\tt coqc} options {\tt -I} or {\tt -R} (see -Section~\ref{coqoptions}). Also, when an interactive {\Coq} session -starts, a library of root {\tt Top} is started, unless option {\tt --top} or {\tt -notop} is set (see Section~\ref{coqoptions}). - -As library files are stored on the file system of the underlying -operating system, a translation from file-system names to {\Coq} names -is needed. In this translation, names in the file system are called -{\em physical} paths while {\Coq} names are contrastingly called {\em -logical} names. Logical names are mapped to physical paths using the -commands {\tt Add LoadPath} or {\tt Add Rec LoadPath} (see -Sections~\ref{AddLoadPath} and~\ref{AddRecLoadPath}). - -\subsection{Qualified names -\label{LongNames} -\index{Qualified identifiers} -\index{Absolute names}} - -Library files are modules which possibly contain submodules which -eventually contain constructions (axioms, parameters, definitions, -lemmas, theorems, remarks or facts). The {\em absolute name}, or {\em -full name}, of a construction in some library file is a qualified -identifier starting with the logical name of the library file, -followed by the sequence of submodules names encapsulating the -construction and ended by the proper name of the construction. -Typically, the absolute name {\tt Coq.Init.Logic.eq} denotes Leibniz' -equality defined in the module {\tt Logic} in the sublibrary {\tt -Init} of the standard library of \Coq. - -The proper name that ends the name of a construction is the {\it short -name} (or sometimes {\it base name}) of the construction (for -instance, the short name of {\tt Coq.Init.Logic.eq} is {\tt eq}). Any -partial suffix of the absolute name is a {\em partially qualified name} -(e.g. {\tt Logic.eq} is a partially qualified name for {\tt -Coq.Init.Logic.eq}). Especially, the short name of a construction is -its shortest partially qualified name. - -{\Coq} does not accept two constructions (definition, theorem, ...) -with the same absolute name but different constructions can have the -same short name (or even same partially qualified names as soon as the -full names are different). - -Notice that the notion of absolute, partially qualified and -short names also applies to library file names. - -\paragraph{Visibility} - -{\Coq} maintains a table called {\it name table} which maps partially -qualified names of constructions to absolute names. This table is -updated by the commands {\tt Require} (see \ref{Require}), {\tt -Import} and {\tt Export} (see \ref{Import}) and also each time a new -declaration is added to the context. An absolute name is called {\it -visible} from a given short or partially qualified name when this -latter name is enough to denote it. This means that the short or -partially qualified name is mapped to the absolute name in {\Coq} name -table. - -A similar table exists for library file names. It is updated by the -vernacular commands {\tt Add LoadPath} and {\tt Add Rec LoadPath} (or -their equivalent as options of the {\Coq} executables, {\tt -I} and -{\tt -R}). - -It may happen that a visible name is hidden by the short name or a -qualified name of another construction. In this case, the name that -has been hidden must be referred to using one more level of -qualification. To ensure that a construction always remains -accessible, absolute names can never be hidden. - -Examples: -\begin{coq_eval} -Reset Initial. -\end{coq_eval} -\begin{coq_example} -Check 0. -Definition nat := bool. -Check 0. -Check Datatypes.nat. -Locate nat. -\end{coq_example} - -\SeeAlso Command {\tt Locate} in Section~\ref{Locate} and {\tt Locate -Library} in Section~\ref{Locate Library}. - -%% \paragraph{The special case of remarks and facts} -%% -%% In contrast with definitions, lemmas, theorems, axioms and parameters, -%% the absolute name of remarks includes the segment of sections in which -%% it is defined. Concretely, if a remark {\tt R} is defined in -%% subsection {\tt S2} of section {\tt S1} in module {\tt M}, then its -%% absolute name is {\tt M.S1.S2.R}. The same for facts, except that the -%% name of the innermost section is dropped from the full name. Then, if -%% a fact {\tt F} is defined in subsection {\tt S2} of section {\tt S1} -%% in module {\tt M}, then its absolute name is {\tt M.S1.F}. - -\section{Implicit arguments -\index{Implicit arguments} -\label{Implicit Arguments}} - -An implicit argument of a function is an argument which can be -inferred from contextual knowledge. There are different kinds of -implicit arguments that can be considered implicit in different -ways. There are also various commands to control the setting or the -inference of implicit arguments. - -\subsection{The different kinds of implicit arguments} - -\subsubsection{Implicit arguments inferable from the knowledge of other -arguments of a function} - -The first kind of implicit arguments covers the arguments that are -inferable from the knowledge of the type of other arguments of the -function, or of the type of the surrounding context of the -application. Especially, such implicit arguments correspond to -parameters dependent in the type of the function. Typical implicit -arguments are the type arguments in polymorphic functions. -There are several kinds of such implicit arguments. - -\paragraph{Strict Implicit Arguments.} -An implicit argument can be either strict or non strict. An implicit -argument is said {\em strict} if, whatever the other arguments of the -function are, it is still inferable from the type of some other -argument. Technically, an implicit argument is strict if it -corresponds to a parameter which is not applied to a variable which -itself is another parameter of the function (since this parameter -may erase its arguments), not in the body of a {\tt match}, and not -itself applied or matched against patterns (since the original -form of the argument can be lost by reduction). - -For instance, the first argument of -\begin{quote} -\verb|cons: forall A:Set, A -> list A -> list A| -\end{quote} -in module {\tt List.v} is strict because {\tt list} is an inductive -type and {\tt A} will always be inferable from the type {\tt -list A} of the third argument of {\tt cons}. -On the contrary, the second argument of a term of type -\begin{quote} -\verb|forall P:nat->Prop, forall n:nat, P n -> ex nat P| -\end{quote} -is implicit but not strict, since it can only be inferred from the -type {\tt P n} of the third argument and if {\tt P} is, e.g., {\tt -fun \_ => True}, it reduces to an expression where {\tt n} does not -occur any longer. The first argument {\tt P} is implicit but not -strict either because it can only be inferred from {\tt P n} and {\tt -P} is not canonically inferable from an arbitrary {\tt n} and the -normal form of {\tt P n} (consider e.g. that {\tt n} is {\tt 0} and -the third argument has type {\tt True}, then any {\tt P} of the form -{\tt fun n => match n with 0 => True | \_ => \mbox{\em anything} end} would -be a solution of the inference problem). - -\paragraph{Contextual Implicit Arguments.} -An implicit argument can be {\em contextual} or not. An implicit -argument is said {\em contextual} if it can be inferred only from the -knowledge of the type of the context of the current expression. For -instance, the only argument of -\begin{quote} -\verb|nil : forall A:Set, list A| -\end{quote} -is contextual. Similarly, both arguments of a term of type -\begin{quote} -\verb|forall P:nat->Prop, forall n:nat, P n \/ n = 0| -\end{quote} -are contextual (moreover, {\tt n} is strict and {\tt P} is not). - -\paragraph{Reversible-Pattern Implicit Arguments.} -There is another class of implicit arguments that can be reinferred -unambiguously if all the types of the remaining arguments are -known. This is the class of implicit arguments occurring in the type -of another argument in position of reversible pattern, which means it -is at the head of an application but applied only to uninstantiated -distinct variables. Such an implicit argument is called {\em -reversible-pattern implicit argument}. A typical example is the -argument {\tt P} of {\tt nat\_rec} in -\begin{quote} -{\tt nat\_rec : forall P : nat -> Set, - P 0 -> (forall n : nat, P n -> P (S n)) -> forall x : nat, P x}. -\end{quote} -({\tt P} is reinferable by abstracting over {\tt n} in the type {\tt P n}). - -See Section~\ref{SetReversiblePatternImplicit} for the automatic declaration -of reversible-pattern implicit arguments. - -\subsubsection{Implicit arguments inferable by resolution} - -This corresponds to a class of non dependent implicit arguments that -are solved based on the structure of their type only. - -\subsection{Maximal or non maximal insertion of implicit arguments} - -In case a function is partially applied, and the next argument to be -applied is an implicit argument, two disciplines are applicable. In the -first case, the function is considered to have no arguments furtherly: -one says that the implicit argument is not maximally inserted. In -the second case, the function is considered to be implicitly applied -to the implicit arguments it is waiting for: one says that the -implicit argument is maximally inserted. - -Each implicit argument can be declared to have to be inserted -maximally or non maximally. This can be governed argument per argument -by the command {\tt Implicit Arguments} (see~\ref{ImplicitArguments}) -or globally by the command {\tt Set Maximal Implicit Insertion} -(see~\ref{SetMaximalImplicitInsertion}). See also -Section~\ref{PrintImplicit}. - -\subsection{Casual use of implicit arguments} - -In a given expression, if it is clear that some argument of a function -can be inferred from the type of the other arguments, the user can -force the given argument to be guessed by replacing it by ``{\tt \_}''. If -possible, the correct argument will be automatically generated. - -\begin{ErrMsgs} - -\item \errindex{Cannot infer a term for this placeholder} - - {\Coq} was not able to deduce an instantiation of a ``{\tt \_}''. - -\end{ErrMsgs} - -\subsection{Declaration of implicit arguments for a constant -\comindex{Implicit Arguments}} -\label{ImplicitArguments} - -In case one wants that some arguments of a given object (constant, -inductive types, constructors, assumptions, local or not) are always -inferred by Coq, one may declare once and for all which are the expected -implicit arguments of this object. There are two ways to do this, -a-priori and a-posteriori. - -\subsubsection{Implicit Argument Binders} - -In the first setting, one wants to explicitly give the implicit -arguments of a constant as part of its definition. To do this, one has -to surround the bindings of implicit arguments by curly braces: -\begin{coq_eval} -Reset Initial. -\end{coq_eval} -\begin{coq_example} -Definition id {A : Type} (x : A) : A := x. -\end{coq_example} - -This automatically declares the argument {\tt A} of {\tt id} as a -maximally inserted implicit argument. One can then do as-if the argument -was absent in every situation but still be able to specify it if needed: -\begin{coq_example} -Definition compose {A B C} (g : B -> C) (f : A -> B) := - fun x => g (f x). -Goal forall A, compose id id = id (A:=A). -\end{coq_example} - -The syntax is supported in all top-level definitions: {\tt Definition}, -{\tt Fixpoint}, {\tt Lemma} and so on. For (co-)inductive datatype -declarations, the semantics are the following: an inductive parameter -declared as an implicit argument need not be repeated in the inductive -definition but will become implicit for the constructors of the -inductive only, not the inductive type itself. For example: - -\begin{coq_example} -Inductive list {A : Type} : Type := -| nil : list -| cons : A -> list -> list. -Print list. -\end{coq_example} - -One can always specify the parameter if it is not uniform using the -usual implicit arguments disambiguation syntax. - -\subsubsection{The Implicit Arguments Vernacular Command} - -To set implicit arguments for a constant a-posteriori, one can use the -command: -\begin{quote} -\tt Implicit Arguments {\qualid} [ \nelist{\possiblybracketedident}{} ] -\end{quote} -where the list of {\possiblybracketedident} is the list of parameters -to be declared implicit, each of the identifier of the list being -optionally surrounded by square brackets, then meaning that this -parameter has to be maximally inserted. - -After the above declaration is issued, implicit arguments can just (and -have to) be skipped in any expression involving an application of -{\qualid}. - -\begin{Variants} -\item {\tt Global Implicit Arguments {\qualid} [ \nelist{\possiblybracketedident}{} ] -\comindex{Global Implicit Arguments}} - -Tells to recompute the implicit arguments of {\qualid} after ending of -the current section if any, enforcing the implicit arguments known -from inside the section to be the ones declared by the command. - -\item {\tt Local Implicit Arguments {\qualid} [ \nelist{\possiblybracketedident}{} ] -\comindex{Local Implicit Arguments}} - -When in a module, tells not to activate the implicit arguments of -{\qualid} declared by this commands to contexts that requires the -module. - -\item {\tt \zeroone{Global {\sl |} Local} Implicit Arguments {\qualid} \sequence{[ \nelist{\possiblybracketedident}{} ]}{}} - -For names of constants, inductive types, constructors, lemmas which -can only be applied to a fixed number of arguments (this excludes for -instance constants whose type is polymorphic), multiple lists -of implicit arguments can be given. These lists must be of different -length, and, depending on the number of arguments {\qualid} is applied -to in practice, the longest applicable list of implicit arguments is -used to select which implicit arguments are inserted. - -For printing, the omitted arguments are the ones of the longest list -of implicit arguments of the sequence. - -\end{Variants} - -\Example -\begin{coq_eval} -Reset Initial. -\end{coq_eval} -\begin{coq_example*} -Inductive list (A:Type) : Type := - | nil : list A - | cons : A -> list A -> list A. -\end{coq_example*} -\begin{coq_example} -Check (cons nat 3 (nil nat)). -Implicit Arguments cons [A]. -Implicit Arguments nil [A]. -Check (cons 3 nil). -Fixpoint map (A B:Type) (f:A->B) (l:list A) : list B := - match l with nil => nil | cons a t => cons (f a) (map A B f t) end. -Fixpoint length (A:Type) (l:list A) : nat := - match l with nil => 0 | cons _ m => S (length A m) end. -Implicit Arguments map [A B]. -Implicit Arguments length [[A]]. (* A has to be maximally inserted *) -Check (fun l:list (list nat) => map length l). -Implicit Arguments map [A B] [A] []. -Check (fun l => map length l = map (list nat) nat length l). -\end{coq_example} - -\Rem To know which are the implicit arguments of an object, use the command -{\tt Print Implicit} (see \ref{PrintImplicit}). - -\Rem If the list of arguments is empty, the command removes the -implicit arguments of {\qualid}. - -\subsection{Automatic declaration of implicit arguments for a constant} - -{\Coq} can also automatically detect what are the implicit arguments -of a defined object. The command is just -\begin{quote} -{\tt Implicit Arguments {\qualid} -\comindex{Implicit Arguments}} -\end{quote} -The auto-detection is governed by options telling if strict, -contextual, or reversible-pattern implicit arguments must be -considered or not (see -Sections~\ref{SetStrictImplicit},~\ref{SetContextualImplicit},~\ref{SetReversiblePatternImplicit} -and also~\ref{SetMaximalImplicitInsertion}). - -\begin{Variants} -\item {\tt Global Implicit Arguments {\qualid} -\comindex{Global Implicit Arguments}} - -Tells to recompute the implicit arguments of {\qualid} after ending of -the current section if any. - -\item {\tt Local Implicit Arguments {\qualid} -\comindex{Local Implicit Arguments}} - -When in a module, tells not to activate the implicit arguments of -{\qualid} computed by this declaration to contexts that requires the -module. - -\end{Variants} - -\Example -\begin{coq_eval} -Reset Initial. -\end{coq_eval} -\begin{coq_example*} -Inductive list (A:Set) : Set := - | nil : list A - | cons : A -> list A -> list A. -\end{coq_example*} -\begin{coq_example} -Implicit Arguments cons. -Print Implicit cons. -Implicit Arguments nil. -Print Implicit nil. -Set Contextual Implicit. -Implicit Arguments nil. -Print Implicit nil. -\end{coq_example} - -The computation of implicit arguments takes account of the -unfolding of constants. For instance, the variable {\tt p} below has -type {\tt (Transitivity R)} which is reducible to {\tt forall x,y:U, R x -y -> forall z:U, R y z -> R x z}. As the variables {\tt x}, {\tt y} and -{\tt z} appear strictly in body of the type, they are implicit. - -\begin{coq_example*} -Variable X : Type. -Definition Relation := X -> X -> Prop. -Definition Transitivity (R:Relation) := - forall x y:X, R x y -> forall z:X, R y z -> R x z. -Variables (R : Relation) (p : Transitivity R). -Implicit Arguments p. -\end{coq_example*} -\begin{coq_example} -Print p. -Print Implicit p. -\end{coq_example} -\begin{coq_example*} -Variables (a b c : X) (r1 : R a b) (r2 : R b c). -\end{coq_example*} -\begin{coq_example} -Check (p r1 r2). -\end{coq_example} - -\subsection{Mode for automatic declaration of implicit arguments -\label{Auto-implicit} -\comindex{Set Implicit Arguments} -\comindex{Unset Implicit Arguments}} - -In case one wants to systematically declare implicit the arguments -detectable as such, one may switch to the automatic declaration of -implicit arguments mode by using the command -\begin{quote} -\tt Set Implicit Arguments. -\end{quote} -Conversely, one may unset the mode by using {\tt Unset Implicit -Arguments}. The mode is off by default. Auto-detection of implicit -arguments is governed by options controlling whether strict and -contextual implicit arguments have to be considered or not. - -\subsection{Controlling strict implicit arguments -\comindex{Set Strict Implicit} -\comindex{Unset Strict Implicit} -\label{SetStrictImplicit}} - -When the mode for automatic declaration of implicit arguments is on, -the default is to automatically set implicit only the strict implicit -arguments plus, for historical reasons, a small subset of the non -strict implicit arguments. To relax this constraint and to -set implicit all non strict implicit arguments by default, use the command -\begin{quote} -\tt Unset Strict Implicit. -\end{quote} -Conversely, use the command {\tt Set Strict Implicit} to -restore the original mode that declares implicit only the strict implicit arguments plus a small subset of the non strict implicit arguments. - -In the other way round, to capture exactly the strict implicit arguments and no more than the strict implicit arguments, use the command: -\comindex{Set Strongly Strict Implicit} -\comindex{Unset Strongly Strict Implicit} -\begin{quote} -\tt Set Strongly Strict Implicit. -\end{quote} -Conversely, use the command {\tt Unset Strongly Strict Implicit} to -let the option ``{\tt Strict Implicit}'' decide what to do. - -\Rem In versions of {\Coq} prior to version 8.0, the default was to -declare the strict implicit arguments as implicit. - -\subsection{Controlling contextual implicit arguments -\comindex{Set Contextual Implicit} -\comindex{Unset Contextual Implicit} -\label{SetContextualImplicit}} - -By default, {\Coq} does not automatically set implicit the contextual -implicit arguments. To tell {\Coq} to infer also contextual implicit -argument, use command -\begin{quote} -\tt Set Contextual Implicit. -\end{quote} -Conversely, use command {\tt Unset Contextual Implicit} to -unset the contextual implicit mode. - -\subsection{Controlling reversible-pattern implicit arguments -\comindex{Set Reversible Pattern Implicit} -\comindex{Unset Reversible Pattern Implicit} -\label{SetReversiblePatternImplicit}} - -By default, {\Coq} does not automatically set implicit the reversible-pattern -implicit arguments. To tell {\Coq} to infer also reversible-pattern implicit -argument, use command -\begin{quote} -\tt Set Reversible Pattern Implicit. -\end{quote} -Conversely, use command {\tt Unset Reversible Pattern Implicit} to -unset the reversible-pattern implicit mode. - -\subsection{Controlling the insertion of implicit arguments not followed by explicit arguments -\comindex{Set Maximal Implicit Insertion} -\comindex{Unset Maximal Implicit Insertion} -\label{SetMaximalImplicitInsertion}} - -Implicit arguments can be declared to be automatically inserted when a -function is partially applied and the next argument of the function is -an implicit one. In case the implicit arguments are automatically -declared (with the command {\tt Set Implicit Arguments}), the command -\begin{quote} -\tt Set Maximal Implicit Insertion. -\end{quote} -is used to tell to declare the implicit arguments with a maximal -insertion status. By default, automatically declared implicit -arguments are not declared to be insertable maximally. To restore the -default mode for maximal insertion, use command {\tt Unset Maximal -Implicit Insertion}. - -\subsection{Explicit applications -\index{Explicitly given implicit arguments} -\label{Implicits-explicitation} -\index{qualid@{\qualid}}} - -In presence of non strict or contextual argument, or in presence of -partial applications, the synthesis of implicit arguments may fail, so -one may have to give explicitly certain implicit arguments of an -application. The syntax for this is {\tt (\ident:=\term)} where {\ident} -is the name of the implicit argument and {\term} is its corresponding -explicit term. Alternatively, one can locally deactivate the hiding of -implicit arguments of a function by using the notation -{\tt @{\qualid}~{\term}$_1$..{\term}$_n$}. This syntax extension is -given Figure~\ref{fig:explicitations}. -\begin{figure} -\begin{centerframe} -\begin{tabular}{lcl} -{\term} & ++= & @ {\qualid} \nelist{\term}{}\\ -& $|$ & @ {\qualid}\\ -& $|$ & {\qualid} \nelist{\textrm{\textsl{argument}}}{}\\ -\\ -{\textrm{\textsl{argument}}} & ::= & {\term} \\ -& $|$ & {\tt ({\ident}:={\term})}\\ -\end{tabular} -\end{centerframe} -\caption{Syntax for explicitly giving implicit arguments} -\label{fig:explicitations} -\end{figure} - -\noindent {\bf Example (continued): } -\begin{coq_example} -Check (p r1 (z:=c)). -Check (p (x:=a) (y:=b) r1 (z:=c) r2). -\end{coq_example} - -\subsection{Displaying what the implicit arguments are -\comindex{Print Implicit} -\label{PrintImplicit}} - -To display the implicit arguments associated to an object, and to know -if each of them is to be used maximally or not, use the command -\begin{quote} -\tt Print Implicit {\qualid}. -\end{quote} - -\subsection{Explicit displaying of implicit arguments for pretty-printing -\comindex{Set Printing Implicit} -\comindex{Unset Printing Implicit} -\comindex{Set Printing Implicit Defensive} -\comindex{Unset Printing Implicit Defensive}} - -By default the basic pretty-printing rules hide the inferable implicit -arguments of an application. To force printing all implicit arguments, -use command -\begin{quote} -{\tt Set Printing Implicit.} -\end{quote} -Conversely, to restore the hiding of implicit arguments, use command -\begin{quote} -{\tt Unset Printing Implicit.} -\end{quote} - -By default the basic pretty-printing rules display the implicit arguments that are not detected as strict implicit arguments. This ``defensive'' mode can quickly make the display cumbersome so this can be deactivated by using the command -\begin{quote} -{\tt Unset Printing Implicit Defensive.} -\end{quote} -Conversely, to force the display of non strict arguments, use command -\begin{quote} -{\tt Set Printing Implicit Defensive.} -\end{quote} - -\SeeAlso {\tt Set Printing All} in Section~\ref{SetPrintingAll}. - -\subsection{Interaction with subtyping} - -When an implicit argument can be inferred from the type of more than -one of the other arguments, then only the type of the first of these -arguments is taken into account, and not an upper type of all of -them. As a consequence, the inference of the implicit argument of -``='' fails in - -\begin{coq_example*} -Check nat = Prop. -\end{coq_example*} - -but succeeds in - -\begin{coq_example*} -Check Prop = nat. -\end{coq_example*} - - - - -\subsection{Canonical structures -\comindex{Canonical Structure}} - -A canonical structure is an instance of a record/structure type that -can be used to solve equations involving implicit arguments. Assume -that {\qualid} denotes an object $(Build\_struc~ c_1~ \ldots~ c_n)$ in the -structure {\em struct} of which the fields are $x_1$, ..., -$x_n$. Assume that {\qualid} is declared as a canonical structure -using the command -\begin{quote} -{\tt Canonical Structure {\qualid}.} -\end{quote} -Then, each time an equation of the form $(x_i~ -\_)=_{\beta\delta\iota\zeta}c_i$ has to be solved during the -type-checking process, {\qualid} is used as a solution. Otherwise -said, {\qualid} is canonically used to extend the field $c_i$ into a -complete structure built on $c_i$. - -Canonical structures are particularly useful when mixed with -coercions and strict implicit arguments. Here is an example. -\begin{coq_example*} -Require Import Relations. -Require Import EqNat. -Set Implicit Arguments. -Unset Strict Implicit. -Structure Setoid : Type := - {Carrier :> Set; - Equal : relation Carrier; - Prf_equiv : equivalence Carrier Equal}. -Definition is_law (A B:Setoid) (f:A -> B) := - forall x y:A, Equal x y -> Equal (f x) (f y). -Axiom eq_nat_equiv : equivalence nat eq_nat. -Definition nat_setoid : Setoid := Build_Setoid eq_nat_equiv. -Canonical Structure nat_setoid. -\end{coq_example*} - -Thanks to \texttt{nat\_setoid} declared as canonical, the implicit -arguments {\tt A} and {\tt B} can be synthesized in the next statement. -\begin{coq_example} -Lemma is_law_S : is_law S. -\end{coq_example} - -\Rem If a same field occurs in several canonical structure, then -only the structure declared first as canonical is considered. - -\begin{Variants} -\item {\tt Canonical Structure {\ident} := {\term} : {\type}.}\\ - {\tt Canonical Structure {\ident} := {\term}.}\\ - {\tt Canonical Structure {\ident} : {\type} := {\term}.} - -These are equivalent to a regular definition of {\ident} followed by -the declaration - -{\tt Canonical Structure {\ident}}. -\end{Variants} - -\SeeAlso more examples in user contribution \texttt{category} -(\texttt{Rocq/ALGEBRA}). - -\subsubsection{Print Canonical Projections. -\comindex{Print Canonical Projections}} - -This displays the list of global names that are components of some -canonical structure. For each of them, the canonical structure of -which it is a projection is indicated. For instance, the above example -gives the following output: - -\begin{coq_example} -Print Canonical Projections. -\end{coq_example} - -\subsection{Implicit types of variables} -\comindex{Implicit Types} - -It is possible to bind variable names to a given type (e.g. in a -development using arithmetic, it may be convenient to bind the names -{\tt n} or {\tt m} to the type {\tt nat} of natural numbers). The -command for that is -\begin{quote} -\tt Implicit Types \nelist{\ident}{} : {\type} -\end{quote} -The effect of the command is to automatically set the type of bound -variables starting with {\ident} (either {\ident} itself or -{\ident} followed by one or more single quotes, underscore or digits) -to be {\type} (unless the bound variable is already declared with an -explicit type in which case, this latter type is considered). - -\Example -\begin{coq_example} -Require Import List. -Implicit Types m n : nat. -Lemma cons_inj_nat : forall m n l, n :: l = m :: l -> n = m. -intros m n. -Lemma cons_inj_bool : forall (m n:bool) l, n :: l = m :: l -> n = m. -\end{coq_example} - -\begin{Variants} -\item {\tt Implicit Type {\ident} : {\type}}\\ -This is useful for declaring the implicit type of a single variable. -\item - {\tt Implicit Types\,% -(\,{\ident$_{1,1}$}\ldots{\ident$_{1,k_1}$}\,{\tt :}\,{\term$_1$} {\tt )}\,% -\ldots\,{\tt (}\,{\ident$_{n,1}$}\ldots{\ident$_{n,k_n}$}\,{\tt :}\,% -{\term$_n$} {\tt )}.}\\ - Adds $n$ blocks of implicit types with different specifications. -\end{Variants} - - -\subsection{Implicit generalization -\label{implicit-generalization} -\comindex{Generalizable Variables}} - -Implicit generalization is an automatic elaboration of a statement with -free variables into a closed statement where these variables are -quantified explicitly. Implicit generalization is done inside binders -starting with a \verb|`| and terms delimited by \verb|`{ }| and -\verb|`( )|, always introducing maximally inserted implicit arguments for -the generalized variables. Inside implicit generalization -delimiters, free variables in the current context are automatically -quantified using a product or a lambda abstraction to generate a closed -term. In the following statement for example, the variables \texttt{n} -and \texttt{m} are automatically generalized and become explicit -arguments of the lemma as we are using \verb|`( )|: - -\begin{coq_example} -Generalizable All Variables. -Lemma nat_comm : `(n = n + 0). -\end{coq_example} -\begin{coq_eval} -Abort. -\end{coq_eval} -One can control the set of generalizable identifiers with the -\texttt{Generalizable} vernacular command to avoid unexpected -generalizations when mistyping identifiers. There are three variants of -the command: - -\begin{quote} -{\tt (Global)? Generalizable (All|No) Variable(s)? ({\ident$_1$ \ident$_n$})?.} -\end{quote} - -\begin{Variants} -\item {\tt Generalizable All Variables.} All variables are candidate for - generalization if they appear free in the context under a - generalization delimiter. This may result in confusing errors in - case of typos. In such cases, the context will probably contain some - unexpected generalized variable. - -\item {\tt Generalizable No Variables.} Disable implicit generalization - entirely. This is the default behavior. - -\item {\tt Generalizable Variable(s)? {\ident$_1$ \ident$_n$}.} - Allow generalization of the given identifiers only. Calling this - command multiple times adds to the allowed identifiers. - -\item {\tt Global Generalizable} Allows to export the choice of - generalizable variables. -\end{Variants} - -One can also use implicit generalization for binders, in which case the -generalized variables are added as binders and set maximally implicit. -\begin{coq_example*} -Definition id `(x : A) : A := x. -\end{coq_example*} -\begin{coq_example} -Print id. -\end{coq_example} - -The generalizing binders \verb|`{ }| and \verb|`( )| work similarly to -their explicit counterparts, only binding the generalized variables -implicitly, as maximally-inserted arguments. In these binders, the -binding name for the bound object is optional, whereas the type is -mandatory, dually to regular binders. - -\section{Coercions -\label{Coercions} -\index{Coercions}} - -Coercions can be used to implicitly inject terms from one {\em class} in -which they reside into another one. A {\em class} is either a sort -(denoted by the keyword {\tt Sortclass}), a product type (denoted by the -keyword {\tt Funclass}), or a type constructor (denoted by its name), -e.g. an inductive type or any constant with a type of the form -\texttt{forall} $(x_1:A_1) .. (x_n:A_n),~s$ where $s$ is a sort. - -Then the user is able to apply an -object that is not a function, but can be coerced to a function, and -more generally to consider that a term of type A is of type B provided -that there is a declared coercion between A and B. The main command is -\comindex{Coercion} -\begin{quote} -\tt Coercion {\qualid} : {\class$_1$} >-> {\class$_2$}. -\end{quote} -which declares the construction denoted by {\qualid} as a -coercion between {\class$_1$} and {\class$_2$}. - -More details and examples, and a description of the commands related -to coercions are provided in Chapter~\ref{Coercions-full}. - -\section[Printing constructions in full]{Printing constructions in full\label{SetPrintingAll} -\comindex{Set Printing All} -\comindex{Unset Printing All}} - -Coercions, implicit arguments, the type of pattern-matching, but also -notations (see Chapter~\ref{Addoc-syntax}) can obfuscate the behavior -of some tactics (typically the tactics applying to occurrences of -subterms are sensitive to the implicit arguments). The command -\begin{quote} -{\tt Set Printing All.} -\end{quote} -deactivates all high-level printing features such as coercions, -implicit arguments, returned type of pattern-matching, notations and -various syntactic sugar for pattern-matching or record projections. -Otherwise said, {\tt Set Printing All} includes the effects -of the commands {\tt Set Printing Implicit}, {\tt Set Printing -Coercions}, {\tt Set Printing Synth}, {\tt Unset Printing Projections} -and {\tt Unset Printing Notations}. To reactivate the high-level -printing features, use the command -\begin{quote} -{\tt Unset Printing All.} -\end{quote} - -\section[Printing universes]{Printing universes\label{PrintingUniverses} -\comindex{Set Printing Universes} -\comindex{Unset Printing Universes}} - -The following command: -\begin{quote} -{\tt Set Printing Universes} -\end{quote} -activates the display of the actual level of each occurrence of -{\Type}. See Section~\ref{Sorts} for details. This wizard option, in -combination with \texttt{Set Printing All} (see -section~\ref{SetPrintingAll}) can help to diagnose failures to unify -terms apparently identical but internally different in the Calculus of -Inductive Constructions. To reactivate the display of the actual level -of the occurrences of {\Type}, use -\begin{quote} -{\tt Unset Printing Universes.} -\end{quote} - -\comindex{Print Universes} - -The constraints on the internal level of the occurrences of {\Type} -(see Section~\ref{Sorts}) can be printed using the command -\begin{quote} -{\tt Print Universes.} -\end{quote} - - -%%% Local Variables: -%%% mode: latex -%%% TeX-master: "Reference-Manual" -%%% End: |