[lojban] Re: Lojban parsing using Common Lisp

[lojban-out@lojban.org]

In the README I give a short walk-through describing how to call the parser.

I don't give instructions on how to setup the Lisp environment, however.

Basically, once you have asdf-install available you can do:

CL-USER> (require 'asdf-install)
("SB-EXECUTABLE" "ASDF-INSTALL")
CL-USER> (asdf-install:install "http://common-lisp.net/project/cl-peg/cl-peg_0.01.tar.gz";)

and then call the parser from the REPL prompt.

(Usage instructions from the README):

Usage:

First create a PEG grammar file, eg:

sentence <-  article? subject verb ( preposition? article? (object / object preposition
object ))
spaces <- [ ]*
article <- spaces ("the" / "the two" / "a")
preposition <- spaces ("on" / "at" / "to" / "with")
subject <- spaces ("man" / "men" / "dog" / "dogs" / "cat")
verb <- spaces ("sat" / "saw" / "shot" / "gave")
object <- spaces ("cannon" / "hat" / "mat")

then create a grammar object and result object:

(require 'cl-peg)
(defvar *mygrammar*)
(defvar *pr*)

CL-USER> (setf *mygrammar* (cl-peg:create-peg-parser "example.peg"))
*MYGRAMMAR*

Now you can parse some input (starting at offset 0):

CL-USER> (setf *pr* (cl-peg:parse *mygrammar* "the cat sat on the mat" 0))
#S(CL-PEG:PR
   :MATCHED T
   :RESULT #S(PV :PE NIL :CHILDREN NIL)
   :ORIGINAL-INPUT "the cat sat on the mat"
   :ORIGINAL-INPUT-OFFSET 0)

Once you have this parse-result you can check whether the parse succeeded:

CL-USER> (cl-peg:pr-matched *pr*)
T

whether all the input was matched (versus some prefix)

CL-USER> (cl-peg:matched-all *pr*)
T

and see the indices of the region matched:

CL-USER> (cl-peg:matched-region *pr*)
(0 22)

or the text:

CL-USER> (cl-peg:pv-input-string *pr* (cl-peg:pr-result *pr*))
"the cat sat on the mat"

To see a detailed parse tree you have to specify keep-parse-result to the parse method:

CL-USER> (setf *pr* (cl-peg:parse *mygrammar* "the cat sat on the mat" 0 t))
<large tree>

For more advanced usage (walking the parse tree or executing lisp code during the parse),
the API is not yet defined. The pv struct is likely to change.

John Leuner

> On Fri, Dec 16, 2005 at 07:41:29AM +0000, jewel@pixie.co.za wrote:
> > I have posted the first version of my Common Lisp PEG parser
> > generator to http://common-lisp.net/project/cl-peg/.
> 
> Go you!
> 
> Does the tarball have good instructions on how to run it?
> 
> -Robin
> 
> -- 
> http://www.digitalkingdom.org/~rlpowell/ *** http://www.lojban.org/
> Reason #237 To Learn Lojban: "Homonyms: Their Grate!"
> Proud Supporter of the Singularity Institute - http://singinst.org/
> 
> 
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> 


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