hackeron@ATHENA.MIT.EDU (03/01/90)
Does anyone know of a compiler/language that allows you to specify changes
to how the language is parsed (in part at least) from withing the program.
I'm thinking of something like having statements in the language that define
how to recognize data types. for example one could have a data type set
that is usually defined as follows:
set1 : set[real] := { 23.0 12.0 34.4 2.3 34.6 2.58 387.2 }
but have a statement in the language that changes the syntax to :
set1$set.real = ( 23.0 12.0 34.4 2.3 34.6 2.58 387.2)
where the things that change are the terminals that separate the sections and
delimit the sections of the definition.
Are there such compilers that can change their parsing grammars (or augment
them) at compile time ?
---Harris
[Fifteen years ago Ned Irons' IMP72 let you stick BNF in the middle of the
program. It worked, but led to some pretty obscure programs since everyone
redefined the syntax all over the place. The compiler was also very slow
since it had to use Earley's algorithm to handle ambiguous syntax. I don't
know if anyone does this sort of thing now. -John]
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Please send responses to the author of the message, not the poster.grunwald@foobar.Colorado.EDU (Dirk Grunwald) (03/03/90)
Well, Scheme and Lisp let you do this using extend-syntax and
defmacro, respectively.
Also, wasn't there a language done at Harvard called Extensible
Language or EL or something like that?
[EL/1, see a subsequent message -John]
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Please send responses to the author of the message, not the poster.arnold@audiofax.com (Arnold Robbins) (03/03/90)
In article <1990Mar1.143905.14553@esegue.segue.boston.ma.us> hackeron@ATHENA.MIT.EDU writes: >Does anyone know of a compiler/language that allows you to specify changes >to how the language is parsed (in part at least) from withing the program. Didn't Algol-68 allow the programmer to change the precedence of operators and such? -- Arnold Robbins -- Senior Research Scientist - AudioFAX 2000 Powers Ferry Road, #220 / Marietta, GA. 30067 INTERNET: arnold@audiofax.com Phone: +1 404 933 7600 UUCP: emory!audfax!arnold Fax: +1 404 933 7606 -- Send compilers articles to compilers@esegue.segue.boston.ma.us {spdcc | ima | lotus}!esegue. Meta-mail to compilers-request@esegue. Please send responses to the author of the message, not the poster.
steve@hubcap.clemson.edu ("Steve" Stevenson) (03/03/90)
hackeron@ATHENA.MIT.EDU writes: >Does anyone know of a compiler/language that allows you to specify changes >to how the language is parsed (in part at least) from withing the program. Way back in the Jurassic age, there was a lot of work by Cheatham and Wegbreit in ``extensible languages.'' Sorry, no direct references come to mind, although I seem to recall a CACM article by Wegbreit on ``EL1'' -- Steve (really "D. E.") Stevenson steve@hubcap.clemson.edu Department of Computer Science, (803)656-5880.mabell Clemson University, Clemson, SC 29634-1906 -- Send compilers articles to compilers@esegue.segue.boston.ma.us {spdcc | ima | lotus}!esegue. Meta-mail to compilers-request@esegue. Please send responses to the author of the message, not the poster.
dhw@itivax.iti.org (David H. West) (03/03/90)
In article <1990Mar1.143905.14553@esegue.segue.boston.ma.us> hackeron@ATHENA.MIT.EDU writes: >Does anyone know of a compiler/language that allows you to specify changes >to how the language is parsed (in part at least) from withing the program. Edinburgh-derived Prologs have a precedence grammar that can be changed at runtime (though not all implementations let you change everything); the interesting part of it is that you can change operators between prefix, infix and postfix, and the system will, if you wish, respect the new conventions on output also. This makes reading and writing (certains kinds of) unusually-formatted stuff almost painless. I once threw together a tiny natural-language-like interface in a great hurry by this means. (Emphasis on TINY). Some functional languages of UK origin have similar facilities. -- Send compilers articles to compilers@esegue.segue.boston.ma.us {spdcc | ima | lotus}!esegue. Meta-mail to compilers-request@esegue. Please send responses to the author of the message, not the poster.
pgl@cup.portal.com (03/03/90)
> Does anyone know of a compiler/language that allows you to specify changes > to how the language is parsed (in part at least) from withing the program. Sure: Prolog allows (re)defining operators. In addition, IBM-Prolog allows specifying various other syntax items, by changing its scan tables and its table of "assignable atoms". For example, it allows the Edinburgh syntax: a([X|_y],_) :- b(X), !, c(X,_y) . and, by simply changing these tables and defining different operators, the default IBM syntax, modified for keyboards without square brackets: a({X!*y},*) <- b(X) & / & c(X,*y) . What's more, you can input a clause in one syntax, change the syntax and then get the clause back in the new syntax (using clause/2 or ax(*,*)). The parser is quite fast because during processing, all atoms must be hashed anyway, so comparing against an "assignable atom" is just a pointer comparison. - peter ludemann pgl@cup.portal.com [standard disclaimer] -- Send compilers articles to compilers@esegue.segue.boston.ma.us {spdcc | ima | lotus}!esegue. Meta-mail to compilers-request@esegue. Please send responses to the author of the message, not the poster.
ipser@vaxa.isi.edu (Ed Ipser) (03/03/90)
In article <1990Mar1.143905.14553@esegue.segue.boston.ma.us> hackeron@ATHENA.MIT.EDU writes: >Does anyone know of a compiler/language that allows you to specify changes >to how the language is parsed (in part at least) from withing the program. >I'm thinking of something like having statements in the language that define >how to recognize data types. for example one could have a data type set >that is usually defined as follows: The proceedings of the '69 and '71 Extensible Language Symposiums were published in SIGPLAN issues volume 4, number 8, August '69 and volume 6, number 12, December '71, respectively. I think that you will find what you are looking for in these issues. -- Send compilers articles to compilers@esegue.segue.boston.ma.us {spdcc | ima | lotus}!esegue. Meta-mail to compilers-request@esegue. Please send responses to the author of the message, not the poster.
PIRINEN@CC.HELSINKI.FI (Pekka P. Pirinen) (03/04/90)
In article <1990Mar1.143905.14553@esegue.segue.boston.ma.us>, hackeron@ATHENA.MIT.EDU writes: > Does anyone know of a compiler/language that allows you to specify changes > to how the language is parsed (in part at least) from withing the program. Most Lisp dialects have this ability. Lisp has evolved as the language of the AI research people, and devising new languages has always been a favorite technique of AI -- which is why it's easy in Lisp. (Yes, I believe in evolution: Lisp programs are sexier!) But then, the Lisp approach to parsing is unusual: - the structure of a program is defined in terms of data structures - the compiler is required to take these data structures as input Therefore the compiler usually works quite independently of the parser (which, I guess, makes this reply inappropriate for comp.compilers :-) - data structures have an external representation in terms of sequences of characters The agent in a Lisp system that creates data structures by reading sequences of characters is called 'the reader'. Most Lisps have a programmable reader, meaning you can define the reader to call a user-defined function when, say, encountering a certain character. This function can then read more characters (possibly by recursive calls to the reader), construct and return a data object. Since the full power of the language is available, this is a pretty powerful feature! For a modern implementation of this, see Guy L. Steele, Jr.: _Common Lisp, the Language_ chapter 22.1. Pekka P. Pirinen University of Helsinki Internet: pirinen@cc.helsinki.fi BITNET: pirinen@finuh UUCP: mcvax!cc.helsinki.fi!pirinen -- Send compilers articles to compilers@esegue.segue.boston.ma.us {spdcc | ima | lotus}!esegue. Meta-mail to compilers-request@esegue. Please send responses to the author of the message, not the poster.