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Extensible PEG Syntax

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* module/ice-9/peg/codegen.scm: Make the PEG syntax extensible, and
    move most of the current code generators to the new interface
* doc/ref/api-peg.texi: Document PEG extensions in the PEG Internals
    section of the manual
This commit is contained in:
Noah Lavine 2011-03-31 17:04:06 -04:00 • committed by Andy Wingo
parent bbc5564c42
commit 94e8517c16
2 changed files with 133 additions and 75 deletions
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32
doc/ref/api-peg.texi
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@ -992,3 +992,35 @@ interface.
The above function can be used to match a string by running
@code{(peg-parse match-a-b "ab")}.
@subsubheading Code Generators and Extensible Syntax
PEG expressions, such as those in a @code{define-nonterm} form, are
interpreted internally in two steps.
First, any string PEG is expanded into an s-expression PEG by the code
in the @code{(ice-9 peg string-peg)} module.
Then, then s-expression PEG that results is compiled into a parsing
function by the @code{(ice-9 peg codegen)} module. In particular, the
function @code{peg-sexp-compile} is called on the s-expression. It then
decides what to do based on the form it is passed.
The PEG syntax can be expanded by providing @code{peg-sexp-compile} more
options for what to do with its forms. The extended syntax will be
associated with a symbol, for instance @code{my-parsing-form}, and will
be called on all PEG expressions of the form
@lisp
(my-parsing-form ...)
@end lisp
The parsing function should take two arguments. The first will be a
syntax object containing a list with all of the arguments to the form
(but not the form's name), and the second will be the
@code{capture-type} argument that is passed to @code{define-nonterm}.
New functions can be registered by calling @code{(add-peg-compiler!
symbol function)}, where @code{symbol} is the symbol that will indicate
a form of this type and @code{function} is the code generating function
described above. The function @code{add-peg-compiler!} is exported from
the @code{(ice-9 peg codegen)} module.