RE: Generalized parser without generation

> James Moughan asked:
>
> > A friend of mine has been given a final year project for which his
> > supervisor wants the above; that is, a program which can read in a
> > description of a grammar then parse a file using it directly. Users
> > must be able to add new grammars at any time without compiling. He
> > has been told that this should be easy to find on the net, but this
> > doesn't seem to be the case, and I certainly don't believe it. Does
> > anyone know if such a tool exists, and if so, can they point me in the
> > right direction?
>
> Meta-S grammars can be loaded at run-time, and even their
> reduction event code can be interpreted, rather than fired in
> compiled code.


I'll add that the ABN2CPP.EXE utility in the Meta-S distribution comes with
source code, and basically does what you describe as being your friend's
project's goal. From the documentation of ABN2CPP.EXE:


Syntax 3


ABN2CPP grammarfile.abn /i inputfile [/ms | /ma]


This version of the command line syntax does the following:


    * loads the .ABN format file grammarfile.abn


    * parses grammarfile.abn with the A-BNF parser


    * if sucessful, loads the file inputfile


    * if the option /ms is specified, scans inputfile for the first substring
that satisfies the grammar specified by grammarfile.abn


* if the option /ma is specified (which it is by default if neither /ms or
/ma are supplied), attempts to accept the entirety of inputfile


This version of the syntax can be used as a kind of very powerful grep
utility, or as a means of testing a grammar against a number of test input
files from the command line, which may be useful in automated regression
testing of a grammar in a build script. (If the .ABN file contains Lua code,
this version of the syntax also interprets the Lua events during the parse.)


--
Quinn Tyler Jackson


http://members.shaw.ca/qjackson/

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