Chapter 12 Syntax extensions and interpretation scopes
In this chapter, we introduce advanced commands to modify the way Coq parses and prints objects, i.e. the translations between the concrete and internal representations of terms and commands. The main commands are Notation and Infix which are described in section 12.1. It also happens that the same symbolic notation is expected in different contexts. To achieve this form of overloading, Coq offers a notion of interpretation scope. This is described in Section 12.2.
Remark: The commands Grammar, Syntax and Distfix which
were present for a while in Coq are no longer available from Coq
version 8.0. The underlying AST structure is also no longer available.
The functionalities of the command Syntactic Definition are
still available, see Section 12.3.
12.1 Notations
12.1.1 Basic notations
A notation is a symbolic abbreviation denoting some term or term pattern.
A typical notation is the use of the infix symbol /\
to denote
the logical conjunction (and). Such a notation is declared
by
The expression (and A B) is the abbreviated term and the
string "A /\ B"
(called a notation) tells how it is
symbolically written.
A notation is always surrounded by double quotes (excepted when the
abbreviation is a single identifier, see 12.3). The
notation is composed of tokens separated by spaces. Identifiers
in the string (such as A and B) are the parameters of the notation. They must occur at least once each in the
denoted term. The other elements of the string (such as /\
) are
the symbols.
An identifier can be used as a symbol but it must be surrounded by simple quotes to avoid the confusion with a parameter. Similarly, every symbol of at least 3 characters and starting with a simple quote must be quoted (then it starts by two single quotes). Here is an example.
A notation binds a syntactic expression to a term. Unless the parser and prettyprinter of Coq already know how to deal with the syntactic expression (see 12.1.7), explicit precedences and associativity rules have to be given.
12.1.2 Precedences and associativity
Mixing different symbolic notations in a same text may cause serious parsing ambiguity. To deal with the ambiguity of notations, Coq uses precedence levels ranging from 0 to 100 (plus one extra level numbered 200) and associativity rules.
Consider for example the new notation
Clearly, an expression such as forall A:Prop, True /\
A \/
A \/
False is ambiguous. To tell the Coq parser how to
interpret the expression, a priority between the symbols /\
and
\/
has to be given. Assume for instance that we want conjunction
to bind more than disjunction. This is expressed by assigning a
precedence level to each notation, knowing that a lower level binds
more than a higher level. Hence the level for disjunction must be
higher than the level for conjunction.
Since connectives are the less tight articulation points of a text, it is reasonable to choose levels not so far from the higher level which is 100, for example 85 for disjunction and 80 for conjunction^{1}.
Similarly, an associativity is needed to decide whether True /\
False /\
False defaults to True /\
(False
/\
False) (right associativity) or to (True
/\
False) /\
False (left associativity). We may
even consider that the expression is not wellformed and that
parentheses are mandatory (this is a “no associativity”)^{2}.
We don’t know of a special convention of the associativity of
disjunction and conjunction, let’s apply for instance a right
associativity (which is the choice of Coq).
Precedence levels and associativity rules of notations have to be given between parentheses in a list of modifiers that the Notation command understands. Here is how the previous examples refine.
Coq < Notation "A \/ B" := (or A B) (at level 85, right associativity).
By default, a notation is considered non associative, but the precedence level is mandatory (except for special cases whose level is canonical). The level is either a number or the mention next level whose meaning is obvious. The list of levels already assigned is on Figure 3.1.
12.1.3 Complex notations
Notations can be made from arbitrarily complex symbols. One can for instance define prefix notations.
One can also define notations for incomplete terms, with the hole expected to be inferred at typing time.
One can define closed notations whose both sides are symbols. In this case, the default precedence level for inner subexpression is 200.
One can also define notations for binders.
In the last case though, there is a conflict with the notation for
type casts. This last notation, as shown by the command Print Grammar
constr is at level 100. To avoid x : A
being parsed as a type cast,
it is necessary to put x at a level below 100, typically 99. Hence, a
correct definition is
See the next section for more about factorization.
12.1.4 Simple factorization rules
Coq extensible parsing is performed by Camlp5 which is essentially a LL1 parser. Hence, some care has to be taken not to hide already existing rules by new rules. Some simple left factorization work has to be done. Here is an example.
Coq < Notation "x < y < z" := (x < y /\ y < z) (at level 70).
In order to factorize the left part of the rules, the subexpression referred by y has to be at the same level in both rules. However the default behavior puts y at the next level below 70 in the first rule (no associativity is the default), and at the level 200 in the second rule (level 200 is the default for inner expressions). To fix this, we need to force the parsing level of y, as follows.
Coq < Notation "x < y < z" := (x < y /\ y < z) (at level 70, y at next level).
For the sake of factorization with Coq predefined rules, simple rules have to be observed for notations starting with a symbol: e.g. rules starting with “{” or “(” should be put at level 0. The list of Coq predefined notations can be found in Chapter 3.
The command to display the current state of the Coq term parser is
Print Grammar constr.
Variant:
Print Grammar pattern.
This displays the state of the subparser of patterns (the parser
used in the grammar of the match with constructions).
12.1.5 Displaying symbolic notations
The command Notation has an effect both on the Coq parser and on the Coq printer. For example:
True /\ True
: Prop
However, printing, especially prettyprinting, requires more care than parsing. We may want specific indentations, line breaks, alignment if on several lines, etc.
The default printing of notations is very rudimentary. For printing a notation, a formatting box is opened in such a way that if the notation and its arguments cannot fit on a single line, a line break is inserted before the symbols of the notation and the arguments on the next lines are aligned with the argument on the first line.
A first, simple control that a user can have on the printing of a notation is the insertion of spaces at some places of the notation. This is performed by adding extra spaces between the symbols and parameters: each extra space (other than the single space needed to separate the components) is interpreted as a space to be inserted by the printer. Here is an example showing how to add spaces around the bar of the notation.
(at level 0, x at level 99).
Coq < Check (sig (fun x : nat => x=x)).
{{x : nat  x = x}}
: Set
The second, more powerful control on printing is by using the format modifier. Here is an example
(at level 200, right associativity, format
"'[v ' 'If' c1 '/' '[' 'then' c2 ']' '/' '[' 'else' c3 ']' ']'").
Identifier 'If' now a keyword
A format is an extension of the string denoting the notation with the possible following elements delimited by single quotes:
 extra spaces are translated into simple spaces
 tokens of the form
'/ '
are translated into breaking point, in case a line break occurs, an indentation of the number of spaces after the “/
” is applied (2 spaces in the given example)  token of the form
'//'
force writing on a new line  wellbracketed pairs of tokens of the form
'[ '
and']'
are translated into printing boxes; in case a line break occurs, an extra indentation of the number of spaces given after the “[
” is applied (4 spaces in the example)  wellbracketed pairs of tokens of the form
'[hv '
and']'
are translated into horizontalorelsevertical printing boxes; if the content of the box does not fit on a single line, then every breaking point forces a newline and an extra indentation of the number of spaces given after the “[
” is applied at the beginning of each newline (3 spaces in the example)  wellbracketed pairs of tokens of the form
'[v '
and']'
are translated into vertical printing boxes; every breaking point forces a newline, even if the line is large enough to display the whole content of the box, and an extra indentation of the number of spaces given after the “[
” is applied at the beginning of each newline
Thus, for the previous example, we get
Notations do not survive the end of sections. No typing of the denoted expression is performed at definition time. Typechecking is done only at the time of use of the notation.
(IF_then_else (IF_then_else True False True)
(IF_then_else True False True)
(IF_then_else True False True)).
If If True
then False
else True
then If True
then False
else True
else If True
then False
else True
: Prop
Remark: Sometimes, a notation is expected only for the parser.
To do so, the option only parsing is allowed in the list of modifiers of
Notation.
Conversely, the only printing can be used to declare that a notation should only be used for printing and should not declare a parsing rule. In particular, such notations do not modify the parser.
12.1.6 The Infix command
The Infix command is a shortening for declaring notations of infix symbols. Its syntax is
Infix "symbol" := qualid ( modifier , … , modifier ).
and it is equivalent to
Notation "x symbol y" := (qualid x y) ( modifier , … , modifier ).
where x and y are fresh names distinct from qualid. Here is an example.
12.1.7 Reserving notations
A given notation may be used in different contexts. Coq expects all uses of the notation to be defined at the same precedence and with the same associativity. To avoid giving the precedence and associativity every time, it is possible to declare a parsing rule in advance without giving its interpretation. Here is an example from the initial state of Coq.
Reserving a notation is also useful for simultaneously defining an inductive type or a recursive constant and a notation for it.
Remark: The notations mentioned on Figure 3.1 are
reserved. Hence their precedence and associativity cannot be changed.
12.1.8 Simultaneous definition of terms and notations
Thanks to reserved notations, the inductive, coinductive, recursive and corecursive definitions can benefit of customized notations. To do this, insert a where notation clause after the definition of the (co)inductive type or (co)recursive term (or after the definition of each of them in case of mutual definitions). The exact syntax is given on Figure 12.1. Here are examples:
where "A /\ B" := (and A B).
match n with
 O => m
 S p => S (p+m)
end
where "n + m" := (plus n m).
12.1.9 Displaying informations about notations
To deactivate the printing of all notations, use the command
Unset Printing Notations.
To reactivate it, use the command
Set Printing Notations.
The default is to use notations for printing terms wherever possible.
See also: Set Printing All in Section 2.9.
12.1.10 Locating notations
To know to which notations a given symbol belongs to, use the command
Locate symbol
where symbol is any (composite) symbol surrounded by double quotes. To locate a particular notation, use a string where the variables of the notation are replaced by “_” and where possible single quotes inserted around identifiers or tokens starting with a single quote are dropped.
Example:
Notation Scope
"'exists' x .. y , p" := ex (fun y => .. (ex (fun y => p)) ..)
: type_scope
(default interpretation)
"'exists' ! x .. y , p" := ex
(unique
(fun y =>
.. (ex (unique (fun y => p))) ..))
: type_scope
(default interpretation)
Coq < Locate "exists _ .. _ , _".
Notation Scope
"'exists' x .. y , p" := ex (fun y => .. (ex (fun y => p)) ..)
: type_scope
(default interpretation)
See also: Section 6.3.10.
sentence ::= [Local] Notation string := term [modifiers] [:scope] .  [Local] Infix string := qualid [modifiers] [:scope] .  [Local] Reserved Notation string [modifiers] .  Inductive ind_body [decl_notation] with … with ind_body [decl_notation].  CoInductive ind_body [decl_notation] with … with ind_body [decl_notation].  Fixpoint fix_body [decl_notation] with … with fix_body [decl_notation] .  CoFixpoint cofix_body [decl_notation] with … with cofix_body [decl_notation] . decl_notation ::= [where string := term [:scope] and … and string := term [:scope]]. modifiers ::= ident , … , ident at level natural  ident , … , ident at next level  at level natural  left associativity  right associativity  no associativity  ident ident  ident binder  ident closed binder  ident global  ident bigint  only parsing  only printing  format string
12.1.11 Notations and simple binders
Notations can be defined for binders as in the example:
The binding variables in the lefthandside that occur as a parameter of the notation naturally bind all their occurrences appearing in their respective scope after instantiation of the parameters of the notation.
Contrastingly, the binding variables that are not a parameter of the notation do not capture the variables of same name that could appear in their scope after instantiation of the notation. E.g., for the notation
the next command fails because p does not bind in the instance of n.
The command has indeed failed with message:
The reference p was not found in the current environment.
Remark: Binding variables must not necessarily be parsed using the
ident entry. For factorization purposes, they can be said to be
parsed at another level (e.g. x in "{ x : A  P }"
must be
parsed at level 99 to be factorized with the notation
"{ A } + { B }"
for which A can be any term).
However, even if parsed as a term, this term must at the end be effectively
a single identifier.
12.1.12 Notations with recursive patterns
A mechanism is provided for declaring elementary notations with recursive patterns. The basic example is:
On the righthand side, an extra construction of the form .. t .. can be used. Notice that .. is part of the Coq syntax and it must not be confused with the threedots notation … used in this manual to denote a sequence of arbitrary size.
On the lefthand side, the part “x s .. s y” of the notation parses any number of time (but at least one time) a sequence of expressions separated by the sequence of tokens s (in the example, s is just “;”).
In the righthand side, the term enclosed within .. must be a pattern with two holes of the form φ([ ]_{E},[ ]_{I}) where the first hole is occupied either by x or by y and the second hole is occupied by an arbitrary term t called the terminating expression of the recursive notation. The subterm .. φ(x,t) .. (or .. φ(y,t) ..) must itself occur at second position of the same pattern where the first hole is occupied by the other variable, y or x. Otherwise said, the righthand side must contain a subterm of the form either φ(x,.. φ(y,t) ..) or φ(y,.. φ(x,t) ..). The pattern φ is the iterator of the recursive notation and, of course, the name x and y can be chosen arbitrarily.
The parsing phase produces a list of expressions which are used to fill in order the first hole of the iterating pattern which is repeatedly nested as many times as the length of the list, the second hole being the nesting point. In the innermost occurrence of the nested iterating pattern, the second hole is finally filled with the terminating expression.
In the example above, the iterator φ([ ]_{E},[ ]_{I}) is cons [ ]_{E} [ ]_{I} and the terminating expression is nil. Here are other examples:
Coq < Notation "[ t * ( x , y , .. , z ) ; ( a , b , .. , c ) * u ]" :=
(pair (pair .. (pair (pair t x) (pair t y)) .. (pair t z))
(pair .. (pair (pair a u) (pair b u)) .. (pair c u)))
(t at level 39).
Recursive patterns can occur several times on the righthand side. Here is an example:
(cons a .. (cons b nil) .., cons b .. (cons a nil) ..).
Notations with recursive patterns can be reserved like standard notations, they can also be declared within interpretation scopes (see section 12.2).
12.1.13 Notations with recursive patterns involving binders
Recursive notations can also be used with binders. The basic example is:
(at level 200, x binder, y binder, right associativity).
The principle is the same as in Section 12.1.12 except that in the iterator φ([ ]_{E},[ ]_{I}), the first hole is a placeholder occurring at the position of the binding variable of a fun or a forall.
To specify that the part “x .. y” of the notation parses a sequence of binders, x and y must be marked as binder in the list of modifiers of the notation. Then, the list of binders produced at the parsing phase are used to fill in the first hole of the iterating pattern which is repeatedly nested as many times as the number of binders generated. If ever the generalization operator ‘ (see Section 2.7.19) is used in the binding list, the added binders are taken into account too.
Binders parsing exist in two flavors. If x and y are marked as binder, then a sequence such as a b c : T will be accepted and interpreted as the sequence of binders (a:T) (b:T) (c:T). For instance, in the notation above, the syntax exists a b : nat, a = b is provided.
The variables x and y can also be marked as closed binder in which case only wellbracketed binders of the form (a b c:T) or {a b c:T} etc. are accepted.
With closed binders, the recursive sequence in the lefthand side can be of the general form x s .. s y where s is an arbitrary sequence of tokens. With open binders though, s has to be empty. Here is an example of recursive notation with closed binders:
(let f := fun x => .. (fun y => t) .. in u)
(at level 200, x closed binder, y closed binder, right associativity).
A recursive pattern for binders can be used in position of a recursive pattern for terms. Here is an example:
(fun x => .. (fun y => (.. (f x) ..) y ) ..)
(at level 200, x binder, y binder, right associativity).
12.1.14 Summary
Syntax of notations
The different syntactic variants of the command Notation are given on Figure 12.1. The optional :scope is described in the Section 12.2.
Remark: No typing of the denoted expression is performed at definition
time. Typechecking is done only at the time of use of the notation.
Remark: Many examples of Notation may be found in the files
composing the initial state of Coq (see directory $COQLIB/theories/Init).
Remark: The notation "{ x }"
has a special status in such a way
that complex notations of the form "x + { y }"
or
"x * { y }"
can be nested with correct precedences. Especially,
every notation involving a pattern of the form "{ x }"
is
parsed as a notation where the pattern "{ x }"
has been simply
replaced by "x"
and the curly brackets are parsed separately.
E.g. "y + { z }"
is not parsed as a term of the given form but
as a term of the form "y + z"
where z
has been parsed
using the rule parsing "{ x }"
. Especially, level and
precedences for a rule including patterns of the form "{ x }"
are relative not to the textual notation but to the notation where the
curly brackets have been removed (e.g. the level and the associativity
given to some notation, say "{ y } & { z }"
in fact applies to
the underlying "{ x }"
free rule which is "y & z"
).
Persistence of notations
Notations do not survive the end of sections. They survive modules unless the command Local Notation is used instead of Notation.
12.2 Interpretation scopes
An interpretation scope is a set of notations for terms with
their interpretation. Interpretation scopes provides with a weak,
purely syntactical form of notations overloading: a same notation, for
instance the infix symbol +
can be used to denote distinct
definitions of an additive operator. Depending on which interpretation
scopes is currently open, the interpretation is different.
Interpretation scopes can include an interpretation for
numerals and strings. However, this is only made possible at the
Objective Caml level.
See Figure 12.1 for the syntax of notations including the possibility to declare them in a given scope. Here is a typical example which declares the notation for conjunction in the scope type_scope.
Notation "A /\ B" := (and A B) : type_scope.
Remark: A notation not defined in a scope is called a lonely notation.
12.2.1 Global interpretation rules for notations
At any time, the interpretation of a notation for term is done within a stack of interpretation scopes and lonely notations. In case a notation has several interpretations, the actual interpretation is the one defined by (or in) the more recently declared (or open) lonely notation (or interpretation scope) which defines this notation. Typically if a given notation is defined in some scope scope but has also an interpretation not assigned to a scope, then, if scope is open before the lonely interpretation is declared, then the lonely interpretation is used (and this is the case even if the interpretation of the notation in scope is given after the lonely interpretation: otherwise said, only the order of lonely interpretations and opening of scopes matters, and not the declaration of interpretations within a scope).
The initial state of Coq declares three interpretation scopes and no lonely notations. These scopes, in opening order, are core_scope, type_scope and nat_scope.
The command to add a scope to the interpretation scope stack is
Open Scope scope.
It is also possible to remove a scope from the interpretation scope stack by using the command
Close Scope scope.
Notice that this command does not only cancel the last Open Scope scope but all the invocation of it.
Remark: Open Scope and Close Scope do not survive the end of
sections where they occur. When defined outside of a section, they are
exported to the modules that import the module where they occur.
Variants:
 Local Open Scope scope.
 Local Close Scope scope.
These variants are not exported to the modules that import the module where they occur, even if outside a section.
 Global Open Scope scope.
 Global Close Scope scope.
These variants survive sections. They behave as if Global were absent when not inside a section.
12.2.2 Local interpretation rules for notations
In addition to the global rules of interpretation of notations, some ways to change the interpretation of subterms are available.
Local opening of an interpretation scope
It is possible to locally extend the interpretation scope stack using the syntax (term)%key (or simply term%key for atomic terms), where key is a special identifier called delimiting key and bound to a given scope.
In such a situation, the term term, and all its subterms, are interpreted in the scope stack extended with the scope bound to key.
To bind a delimiting key to a scope, use the command
Delimit Scope scope with ident
To remove a delimiting key of a scope, use the command
Undelimit Scope scope
Binding arguments of a constant to an interpretation scope
It is possible to set in advance that some arguments of a given constant have to be interpreted in a given scope. The command is
Arguments qualid name%scope … name%scope
where the list is a prefix of the list of the arguments of qualid eventually annotated with their scope. Grouping round parentheses can be used to decorate multiple arguments with the same scope. scope can be either a scope name or its delimiting key. For example the following command puts the first two arguments of plus_fct in the scope delimited by the key F (Rfun_scope) and the last argument in the scope delimited by the key R (R_scope).
The Arguments command accepts scopes decoration to all grouping parentheses. In the following example arguments A and B are marked as maximally inserted implicit arguments and are put into the type_scope scope.
When interpreting a term, if some of the arguments of qualid are built from a notation, then this notation is interpreted in the scope stack extended by the scope bound (if any) to this argument. The effect of the scope is limited to the argument itself. It does not propagate to subterms but the subterms that, after interpretation of the notation, turn to be themselves arguments of a reference are interpreted accordingly to the arguments scopes bound to this reference.
Arguments scopes can be cleared with the following command:
Arguments qualid : clear scopes
Variants:

Global Arguments qualid name%scope … name%scope
This behaves like Arguments qualid name%scope … name%scope but survives when a section is closed instead of stopping working at section closing. Without the Global modifier, the effect of the command stops when the section it belongs to ends.
 Local Arguments qualid name%scope … name%scope
This behaves like Arguments qualid name%scope … name%scope but does not survive modules and files. Without the Local modifier, the effect of the command is visible from within other modules or files.
See also: The command to show the scopes bound to the arguments of a
function is described in Section 2.
Binding types of arguments to an interpretation scope
When an interpretation scope is naturally associated to a type (e.g. the scope of operations on the natural numbers), it may be convenient to bind it to this type. When a scope scope is bound to a type type, any new function defined later on gets its arguments of type type interpreted by default in scope scope (this default behavior can however be overwritten by explicitly using the command Arguments).
Whether the argument of a function has some type type is determined statically. For instance, if f is a polymorphic function of type forall X:Type, X > X and type t is bound to a scope scope, then a of type t in f t a is not recognized as an argument to be interpreted in scope scope.
More generally, any class (see Chapter 18) can be bound to an interpretation scope. The command to do it is
Bind Scope scope with class
Example:
U is declared
Coq < Bind Scope U_scope with U.
Coq < Parameter Uplus : U > U > U.
Uplus is declared
Coq < Parameter P : forall T:Set, T > U > Prop.
P is declared
Coq < Parameter f : forall T:Set, T > U.
f is declared
Coq < Infix "+" := Uplus : U_scope.
Coq < Unset Printing Notations.
Coq < Open Scope nat_scope. (* Define + on the nat as the default for + *)
Coq < Check (fun x y1 y2 z t => P _ (x + t) ((f _ (y1 + y2) + z))).
fun (x y1 y2 : nat) (z : U) (t : nat) =>
P nat (Nat.add x t) (Uplus (f nat (Nat.add y1 y2)) z)
: forall (_ : nat) (_ : nat) (_ : nat) (_ : U) (_ : nat), Prop
Remark: The scope type_scope has also a local effect on
interpretation. See the next section.
See also: The command to show the scopes bound to the arguments of a
function is described in Section 2.
12.2.3 The type_scope interpretation scope
The scope type_scope has a special status. It is a primitive interpretation scope which is temporarily activated each time a subterm of an expression is expected to be a type. This includes goals and statements, types of binders, domain and codomain of implication, codomain of products, and more generally any type argument of a declared or defined constant.
12.2.4 Interpretation scopes used in the standard library of Coq
We give an overview of the scopes used in the standard library of Coq. For a complete list of notations in each scope, use the commands Print Scopes or Print Scope scope.
type_scope
This includes infix * for product types and infix + for sum types. It is delimited by key type.
nat_scope
This includes the standard arithmetical operators and relations on type nat. Positive numerals in this scope are mapped to their canonical representent built from O and S. The scope is delimited by key nat.
N_scope
This includes the standard arithmetical operators and relations on type N (binary natural numbers). It is delimited by key N and comes with an interpretation for numerals as closed term of type Z.
Z_scope
This includes the standard arithmetical operators and relations on type Z (binary integer numbers). It is delimited by key Z and comes with an interpretation for numerals as closed term of type Z.
positive_scope
This includes the standard arithmetical operators and relations on type positive (binary strictly positive numbers). It is delimited by key positive and comes with an interpretation for numerals as closed term of type positive.
Q_scope
This includes the standard arithmetical operators and relations on type Q (rational numbers defined as fractions of an integer and a strictly positive integer modulo the equality of the numeratordenominator crossproduct). As for numerals, only 0 and 1 have an interpretation in scope Q_scope (their interpretations are 0/1 and 1/1 respectively).
Qc_scope
This includes the standard arithmetical operators and relations on the type Qc of rational numbers defined as the type of irreducible fractions of an integer and a strictly positive integer.
real_scope
This includes the standard arithmetical operators and relations on type R (axiomatic real numbers). It is delimited by key R and comes with an interpretation for numerals as term of type R. The interpretation is based on the binary decomposition. The numeral 2 is represented by 1+1. The interpretation φ(n) of an odd positive numerals greater n than 3 is 1+(1+1)*φ((n−1)/2). The interpretation φ(n) of an even positive numerals greater n than 4 is (1+1)*φ(n/2). Negative numerals are represented as the opposite of the interpretation of their absolute value. E.g. the syntactic object 11 is interpreted as (1+(1+1)*((1+1)*(1+(1+1)))) where the unit 1 and all the operations are those of R.
bool_scope
This includes notations for the boolean operators. It is delimited by key bool.
list_scope
This includes notations for the list operators. It is delimited by key list.
core_scope
This includes the notation for pairs. It is delimited by key core.
string_scope
This includes notation for strings as elements of the type string. Special characters and escaping follow Coq conventions on strings (see Section 1.1). Especially, there is no convention to visualize non printable characters of a string. The file String.v shows an example that contains quotes, a newline and a beep (i.e. the ascii character of code 7).
char_scope
This includes interpretation for all strings of the form
"
c"
where c is an ascii character, or of the form
"
nnn"
where nnn is a threedigits number (possibly
with leading 0’s), or of the form """"
. Their respective
denotations are the ascii code of c, the decimal ascii code nnn,
or the ascii code of the character "
(i.e. the ascii code
34), all of them being represented in the type ascii.
12.2.5 Displaying informations about scopes
Print Visibility
This displays the current stack of notations in scopes and lonely notations that is used to interpret a notation. The top of the stack is displayed last. Notations in scopes whose interpretation is hidden by the same notation in a more recently open scope are not displayed. Hence each notation is displayed only once.
Variant:
Print Visibility scope
This displays the current stack of notations in scopes and lonely
notations assuming that scope is pushed on top of the stack. This
is useful to know how a subterm locally occurring in the scope of
scope is interpreted.
Print Scope scope
This displays all the notations defined in interpretation scope scope. It also displays the delimiting key if any and the class to which the scope is bound, if any.
Print Scopes
This displays all the notations, delimiting keys and corresponding class of all the existing interpretation scopes. It also displays the lonely notations.
12.3 Abbreviations
An abbreviation is a name, possibly applied to arguments, that denotes a (presumably) more complex expression. Here are examples:
Coq < Check 1 :: 2 :: 3 :: nil.
[1; 2; 3]
: Nlist
Coq < Notation reflexive R := (forall x, R x x).
Coq < Check forall A:Prop, A <> A.
reflexive iff
: Prop
Coq < Check reflexive iff.
reflexive iff
: Prop
An abbreviation expects no precedence nor associativity, since it
follows the usual syntax of application. Abbreviations are used as
much as possible by the Coq printers unless the modifier
(only parsing)
is given.
Abbreviations are bound to an absolute name as an ordinary definition is, and they can be referred by qualified names too.
Abbreviations are syntactic in the sense that they are bound to expressions which are not typed at the time of the definition of the abbreviation but at the time it is used. Especially, abbreviations can be bound to terms with holes (i.e. with “_”). The general syntax for abbreviations is
[Local] Notation ident [ident ident … ident ident] := term
[(only parsing)] .
Example:
explicit_id is defined
Coq < Notation id := (explicit_id _).
Coq < Check (id 0).
id 0
: nat
Abbreviations do not survive the end of sections. No typing of the denoted expression is performed at definition time. Typechecking is done only at the time of use of the abbreviation.
12.4 Tactic Notations
Tactic notations allow to customize the syntax of the tactics of the
tactic language^{3}. Tactic notations obey the following
syntax
sentence  ::=  [Local] Tactic Notation [tactic_level] [prod_item … prod_item] 
:= tactic .  
prod_item  ::=  string  tactic_argument_type(ident) 
tactic_level  ::=  (at level natural) 
tactic_argument_type  ::=  ident  simple_intropattern  reference 
  hyp  hyp_list  ne_hyp_list  
  constr  uconstr  constr_list  ne_constr_list  
  integer  integer_list  ne_integer_list  
  int_or_var  int_or_var_list  ne_int_or_var_list  
  tactic  tacticn (for 0≤ n≤ 5) 
A tactic notation Tactic Notation tactic_level [prod_item … prod_item] := tactic extends the parser and prettyprinter of tactics with a new rule made of the list of production items. It then evaluates into the tactic expression tactic. For simple tactics, it is recommended to use a terminal symbol, i.e. a string, for the first production item. The tactic level indicates the parsing precedence of the tactic notation. This information is particularly relevant for notations of tacticals. Levels 0 to 5 are available (default is 0). To know the parsing precedences of the existing tacticals, use the command Print Grammar tactic.
Each type of tactic argument has a specific semantic regarding how it is parsed and how it is interpreted. The semantic is described in the following table. The last command gives examples of tactics which use the corresponding kind of argument.
Tactic argument type  parsed as  interpreted as  as in tactic 
ident  identifier  a usergiven name  intro 
simple_intropattern  intro_pattern  an intro_pattern  intros 
hyp  identifier  an hypothesis defined in context  clear 
reference  qualified identifier  a global reference of term  unfold 
constr  term  a term  exact 
uconstr  term  an untyped term  refine 
integer  integer  an integer  
int_or_var  identifier or integer  an integer  do 
tactic  tactic at level 5  a tactic  
tacticn  tactic at level n  a tactic  
entry_list  list of entry  a list of how entry is interpreted  
ne_entry_list  nonempty list of entry  a list of how entry is interpreted 
Remark: In order to be bound in tactic definitions, each syntactic entry
for argument type must include the case of simple L_{tac} identifier
as part of what it parses. This is naturally the case for ident,
simple_intropattern, reference, constr, ... but not
for integer. This is the reason for introducing a special entry
int_or_var which evaluates to integers only but which
syntactically includes identifiers in order to be usable in tactic
definitions.
Remark: The entry_list and ne_entry_list
entries can be used in primitive tactics or in other notations at
places where a list of the underlying entry can be used: entry is
either constr, hyp, integer or
int_or_var.
Tactic notations do not survive the end of sections. They survive modules unless the command Local Tactic Notation is used instead of Tactic Notation.
 1
 which are the levels effectively chosen in the current implementation of Coq
 2
 Coq accepts notations declared as no associative but the parser on which Coq is built, namely Camlp4, currently does not implement the noassociativity and replace it by a left associativity; hence it is the same for Coq: noassociativity is in fact left associativity
 3
 Tactic notations are just a simplification of the Grammar tactic simple_tactic command that existed in versions prior to version 8.0.