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doc: formatting changes

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* doc/bison.texi: Here.
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Akim Demaille
2018-11-25 14:00:41 +01:00
parent e1c55d83f8
commit 9476783307
1 changed files with 55 additions and 63 deletions
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doc/bison.texi
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@@ -4810,18 +4810,16 @@ The basic way to declare a token type name (terminal symbol) is as follows:
%token @var{name}
@end example
Bison will convert this into a @code{#define} directive in
the parser, so that the function @code{yylex} (if it is in this file)
can use the name @var{name} to stand for this token type's code.
Bison will convert this into a @code{#define} directive in the parser, so
that the function @code{yylex} (if it is in this file) can use the name
@var{name} to stand for this token type's code.
Alternatively, you can use @code{%left}, @code{%right},
@code{%precedence}, or
@code{%nonassoc} instead of @code{%token}, if you wish to specify
associativity and precedence. @xref{Precedence Decl, ,Operator
Precedence}.
Alternatively, you can use @code{%left}, @code{%right}, @code{%precedence},
or @code{%nonassoc} instead of @code{%token}, if you wish to specify
associativity and precedence. @xref{Precedence Decl, ,Operator Precedence}.
You can explicitly specify the numeric code for a token type by appending
a nonnegative decimal or hexadecimal integer value in the field immediately
You can explicitly specify the numeric code for a token type by appending a
nonnegative decimal or hexadecimal integer value in the field immediately
following the token name:
@example
@@ -4830,14 +4828,14 @@ following the token name:
@end example
@noindent
It is generally best, however, to let Bison choose the numeric codes for
all token types. Bison will automatically select codes that don't conflict
with each other or with normal characters.
It is generally best, however, to let Bison choose the numeric codes for all
token types. Bison will automatically select codes that don't conflict with
each other or with normal characters.
In the event that the stack type is a union, you must augment the
@code{%token} or other token declaration to include the data type
alternative delimited by angle-brackets (@pxref{Multiple Types, ,More
Than One Value Type}).
alternative delimited by angle-brackets (@pxref{Multiple Types, ,More Than
One Value Type}).
For example:
@@ -4851,9 +4849,9 @@ For example:
@end group
@end example
You can associate a literal string token with a token type name by
writing the literal string at the end of a @code{%token}
declaration which declares the name. For example:
You can associate a literal string token with a token type name by writing
the literal string at the end of a @code{%token} declaration which declares
the name. For example:
@example
%token arrow "=>"
@@ -4872,14 +4870,14 @@ equivalent literal string tokens:
@noindent
Once you equate the literal string and the token name, you can use them
interchangeably in further declarations or the grammar rules. The
@code{yylex} function can use the token name or the literal string to
obtain the token type code number (@pxref{Calling Convention}).
Syntax error messages passed to @code{yyerror} from the parser will reference
the literal string instead of the token name.
@code{yylex} function can use the token name or the literal string to obtain
the token type code number (@pxref{Calling Convention}). Syntax error
messages passed to @code{yyerror} from the parser will reference the literal
string instead of the token name.
The token numbered as 0 corresponds to end of file; the following line
allows for nicer error messages referring to ``end of file'' instead
of ``$end'':
allows for nicer error messages referring to ``end of file'' instead of
``$end'':
@example
%token END 0 "end of file"
@@ -4891,12 +4889,11 @@ of ``$end'':
@cindex declaring operator precedence
@cindex operator precedence, declaring
Use the @code{%left}, @code{%right}, @code{%nonassoc}, or
@code{%precedence} declaration to
declare a token and specify its precedence and associativity, all at
once. These are called @dfn{precedence declarations}.
@xref{Precedence, ,Operator Precedence}, for general information on
operator precedence.
Use the @code{%left}, @code{%right}, @code{%nonassoc}, or @code{%precedence}
declaration to declare a token and specify its precedence and associativity,
all at once. These are called @dfn{precedence declarations}.
@xref{Precedence, ,Operator Precedence}, for general information on operator
precedence.
The syntax of a precedence declaration is nearly the same as that of
@code{%token}: either
@@ -4918,34 +4915,32 @@ all the @var{symbols}:
@itemize @bullet
@item
The associativity of an operator @var{op} determines how repeated uses
of the operator nest: whether @samp{@var{x} @var{op} @var{y} @var{op}
@var{z}} is parsed by grouping @var{x} with @var{y} first or by
grouping @var{y} with @var{z} first. @code{%left} specifies
left-associativity (grouping @var{x} with @var{y} first) and
@code{%right} specifies right-associativity (grouping @var{y} with
@var{z} first). @code{%nonassoc} specifies no associativity, which
means that @samp{@var{x} @var{op} @var{y} @var{op} @var{z}} is
considered a syntax error.
The associativity of an operator @var{op} determines how repeated uses of
the operator nest: whether @samp{@var{x} @var{op} @var{y} @var{op} @var{z}}
is parsed by grouping @var{x} with @var{y} first or by grouping @var{y} with
@var{z} first. @code{%left} specifies left-associativity (grouping @var{x}
with @var{y} first) and @code{%right} specifies right-associativity
(grouping @var{y} with @var{z} first). @code{%nonassoc} specifies no
associativity, which means that @samp{@var{x} @var{op} @var{y} @var{op}
@var{z}} is considered a syntax error.
@code{%precedence} gives only precedence to the @var{symbols}, and
defines no associativity at all. Use this to define precedence only,
and leave any potential conflict due to associativity enabled.
@code{%precedence} gives only precedence to the @var{symbols}, and defines
no associativity at all. Use this to define precedence only, and leave any
potential conflict due to associativity enabled.
@item
The precedence of an operator determines how it nests with other operators.
All the tokens declared in a single precedence declaration have equal
precedence and nest together according to their associativity.
When two tokens declared in different precedence declarations associate,
the one declared later has the higher precedence and is grouped first.
precedence and nest together according to their associativity. When two
tokens declared in different precedence declarations associate, the one
declared later has the higher precedence and is grouped first.
@end itemize
For backward compatibility, there is a confusing difference between the
argument lists of @code{%token} and precedence declarations.
Only a @code{%token} can associate a literal string with a token type name.
A precedence declaration always interprets a literal string as a reference to a
separate token.
For example:
argument lists of @code{%token} and precedence declarations. Only a
@code{%token} can associate a literal string with a token type name. A
precedence declaration always interprets a literal string as a reference to
a separate token. For example:
@example
%left OR "<=" // Does not declare an alias.
@@ -4968,25 +4963,22 @@ used. This is done with a @code{%type} declaration, like this:
@end example
@noindent
Here @var{nonterminal} is the name of a nonterminal symbol, and
@var{type} is the name given in the @code{%union} to the alternative
that you want (@pxref{Union Decl, ,The Union Declaration}). You
can give any number of nonterminal symbols in the same @code{%type}
declaration, if they have the same value type. Use spaces to separate
the symbol names.
Here @var{nonterminal} is the name of a nonterminal symbol, and @var{type}
is the name given in the @code{%union} to the alternative that you want
(@pxref{Union Decl, ,The Union Declaration}). You can give any number of
nonterminal symbols in the same @code{%type} declaration, if they have the
same value type. Use spaces to separate the symbol names.
You can also declare the value type of a terminal symbol. To do this,
use the same @code{<@var{type}>} construction in a declaration for the
terminal symbol. All kinds of token declarations allow
@code{<@var{type}>}.
You can also declare the value type of a terminal symbol. To do this, use
the same @code{<@var{type}>} construction in a declaration for the terminal
symbol. All kinds of token declarations allow @code{<@var{type}>}.
@node Initial Action Decl
@subsection Performing Actions before Parsing
@findex %initial-action
Sometimes your parser needs to perform some initializations before
parsing. The @code{%initial-action} directive allows for such arbitrary
code.
Sometimes your parser needs to perform some initializations before parsing.
The @code{%initial-action} directive allows for such arbitrary code.
@deffn {Directive} %initial-action @{ @var{code} @}
@findex %initial-action