@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990--1995, 1998--1999, 2001--2023 Free Software
+@c Copyright (C) 1990--1995, 1998--1999, 2001--2024 Free Software
@c Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@node Parsing Expression Grammars
@end example
Once defined, grammars can be used to parse text after point in the
-current buffer, in the following ways:
+current buffer, in a number of ways. The @code{peg-parse} macro is the
+simplest:
@defmac peg-parse &rest pexs
-Match @var{pexs} at point. If @var{pexs} is a list of PEG rules, the
-first rule is considered the ``entry-point'':
+Match @var{pexs} at point.
@end defmac
@example
@group
(peg-parse
- ((number sign digit (* digit))
- (sign (or "+" "-" ""))
- (digit [0-9])))
+ (number sign digit (* digit))
+ (sign (or "+" "-" ""))
+ (digit [0-9]))
@end group
@end example
-@c FIXME: These two should be formally defined using @defmac and @defun.
-@findex with-peg-rules
-@findex peg-run
-The @code{peg-parse} macro represents the simplest use of the
-@acronym{PEG} library, but also the least flexible, as the rules must be
-written directly into the source code. A more flexible approach
-involves use of three macros in conjunction: @code{with-peg-rules}, a
-@code{let}-like construct that makes a set of rules available within the
-macro body; @code{peg-run}, which initiates parsing given a single rule;
-and @code{peg}, which is used to wrap the entry-point rule name. In
-fact, a call to @code{peg-parse} expands to just this set of calls. The
-above example could be written as:
+While this macro is simple it is also inflexible, as the rules must be
+written directly into the source code. More flexibility can be gained
+by using a combination of other functions and macros.
+
+@defmac with-peg-rules rules &rest body
+Execute @var{body} with @var{rules}, a list of @acronym{PEX}s, in
+effect. Within @var{BODY}, parsing is initiated with a call to
+@code{peg-run}.
+@end defmac
+
+@defun peg-run peg-matcher &optional failure-function success-function
+This function accepts a single @var{peg-matcher}, which is the result of
+calling @code{peg} (see below) on a named rule, usually the entry-point
+of a larger grammar.
+
+At the end of parsing, one of @var{failure-function} or
+@var{success-function} is called, depending on whether the parsing
+succeeded or not. If @var{success-function} is called, it is passed a
+lambda form that runs all the actions collected on the stack during
+parsing -- by default this lambda form is simply executed. If parsing
+fails, the @var{failure-function} is called with a list of @acronym{PEG}
+expressions that failed during parsing; by default this list is
+discarded.
+@end defun
+
+The @var{peg-matcher} passed to @code{peg-run} is produced by a call to
+@code{peg}:
+
+@defmac peg &rest pexs
+Convert @var{pexs} into a single peg-matcher suitable for passing to
+@code{peg-run}.
+@end defmac
+
+The @code{peg-parse} example above expands to a set of calls to these
+functions, and could be written in full as:
@example
@group
@end group
@end example
-This allows more explicit control over the ``entry-point'' of parsing,
-and allows the combination of rules from different sources.
+This approach allows more explicit control over the ``entry-point'' of
+parsing, and allows the combination of rules from different sources.
-@c FIXME: Use @defmac.
-@findex define-peg-rule
Individual rules can also be defined using a more @code{defun}-like
syntax, using the macro @code{define-peg-rule}:
+@defmac define-peg-rule name args &rest pexs
+Define @var{name} as a PEG rule that accepts @var{args} and matches
+@var{pexs} at point.
+@end defmac
+
+For instance:
+
@example
@group
(define-peg-rule digit ()
@end group
@end example
-This also allows for rules that accept an argument (supplied by the
-@code{funcall} PEG rule, @pxref{PEX Definitions}).
+Arguments can be supplied to rules by the @code{funcall} PEG rule
+(@pxref{PEX Definitions}).
-@c FIXME: Use @defmac.
-@findex define-peg-ruleset
Another possibility is to define a named set of rules with
@code{define-peg-ruleset}:
+@defmac define-peg-ruleset name &rest rules
+Define @var{name} as an identifier for @var{rules}.
+@end defmac
+
@example
@group
(define-peg-ruleset number-grammar
Treats the value of the Lisp expression @var{exp} as a boolean.
@end table
-@c FIXME: peg-char-classes should be mentioned in the text below.
@vindex peg-char-classes
-Character class matching can use the same named character classes as
-in regular expressions (@pxref{Top,, Character Classes,elisp})
+Character-class matching can refer to the classes named in
+@code{peg-char-classes}, equivalent to character classes in regular
+expressions (@pxref{Top,, Character Classes,elisp})
@node Parsing Actions
@section Parsing Actions
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