I guess I could try to add a loop that increments a variable containing the number of time it should read the same rule while it doesn't match the whole string and the number of characters matched increases with the variable... But it looks like going around the problem without really fixing it...
On Tue, Oct 11, 2011 at 7:57 PM, Xavier MONTILLET <[email protected]> wrote: > I just reformated the whole thing and it kind of works. > http://jsfiddle.net/xavierm02/ndDVa/1/ > I get a CST and I think I can manage to turn it into an AST. > But I still have a problem with the CFG... As shown, it works > > But if I change the order of the things to match it fails. At last on > recursive rules. > Here is an example : > > Text > Text Letter > > The code about won't work with my "parser" but if i rewrite it to > avoid having the recursive rule first, it works: > > Text > Letter Text > > The above example works... > > But I'm quite sure I won't always be able to avoid having a recursive > rule as first rule so... Do you guys see anything I could do to avoid > it? > > I tried allowing a given number of recursion before simply returning > false when seeing a recursive rule but if you have more than that > number, it fails :/ > And it I don't do it at all, I get an infinite loop. > > Here's the exact same code except I changed the order in the > declaration of MultiplicativeExpression or AdditiveExpression. > http://jsfiddle.net/xavierm02/ndDVa/2/ > > On Sun, Oct 9, 2011 at 8:16 PM, Xavier MONTILLET > <[email protected]> wrote: >> I figured out how to get something looking like an AST. >> http://jsfiddle.net/xavierm02/HG6Bx/1/ >> But comments and ideas on how to throw errors are still welcome. >> >> On Sun, Oct 9, 2011 at 6:10 PM, Xavier MONTILLET >> <[email protected]> wrote: >>> And how do you throw errors with a CFG ? >>> I mean JSLint does throw errors but the Lexer doesn't use a CFG... >>> If you use a CFG, how do you throw errors ? You take the longest / >>> deepest "possibility" that had a meaning ? >>> >>> On Sun, Oct 9, 2011 at 4:17 PM, Xavier MONTILLET >>> <[email protected]> wrote: >>>> Btw, I have no knowledge in Computer Science at all. So if you know >>>> tutorials / books explaining how to build a parser without needed too >>>> much knowledge, please tell me. Because every single tutorial I tried >>>> to read started with strange formulas I couldn't understand and, >>>> instead of providing pseudo-code, just described what the code should >>>> do, gave mathematical methods which I couldn't understand to check >>>> whether the result was going to be what we wanted or not and so on... >>>> >>>> (I know JavaScript quite well because I started doing websites in >>>> high-school but since I left High-school (last year), I've only been >>>> doing Maths and Physics in "classes preparatoire" (a France-specific >>>> system where you do a lot of Maths / Physics for two years in order to >>>> prepare "contests" which, depending on what your ranking is, will >>>> allow you to choose a given school or not. And I won't be doing any >>>> computer science until then...) >>>> >>>> On Sun, Oct 9, 2011 at 4:05 PM, Xavier MONTILLET >>>> <[email protected]> wrote: >>>>> I've started writing the Lexer and for it I used some kind of CFG. >>>>> But I'm not sure whether I understood the aim of those things >>>>> properly. I mean is the CFG supposed to let you build a syntax tree or >>>>> just a token list ? Because I can't figure out how to build the syntax >>>>> tree from it... >>>>> Anyway, I wrote a CFG for basic Maths : >>>>> >>>>> Digit >>>>> '0' >>>>> '1' >>>>> '2' >>>>> '3' >>>>> '4' >>>>> '5' >>>>> '6' >>>>> '7' >>>>> '8' >>>>> '9' >>>>> >>>>> Operator >>>>> '+' >>>>> '-' >>>>> '*' >>>>> '/' >>>>> >>>>> Expression >>>>> '(' Expression ')' >>>>> Expression Operator Expression >>>>> Number >>>>> >>>>> And as I didn't want to bother writing a parser to parse the CFG for >>>>> my parser, I transformed it in JS : >>>>> >>>>> var rules = ( function ( ) { >>>>> var Digit = [ ]; >>>>> var Expression = [ ]; >>>>> var Operator = [ ]; >>>>> Digit.name = 'Digit'; >>>>> Expression.name = 'Expression'; >>>>> Operator.name = 'Operator'; >>>>> Digit.push( >>>>> [ '0' ], >>>>> [ '1' ], >>>>> [ '2' ], >>>>> [ '3' ], >>>>> [ '4' ], >>>>> [ '5' ], >>>>> [ '6' ], >>>>> [ '7' ], >>>>> [ '8' ], >>>>> [ '9' ] >>>>> ); >>>>> Expression.push( >>>>> [ '(', Expression, ')' ], >>>>> [ Expression, Operator, Expression ], >>>>> [ Digit ] >>>>> ); >>>>> Operator.push( >>>>> [ '+' ], >>>>> [ '-' ], >>>>> [ '*' ], >>>>> [ '/' ] >>>>> ); >>>>> return { >>>>> Digit: Digit, >>>>> Expression: Expression, >>>>> Operator: Operator >>>>> }; >>>>> } )( ); >>>>> >>>>> The name properties are here because I had some infinite loops so it >>>>> was easier to debug with it... >>>>> And I define the arrays before so that I can reference them in others. >>>>> >>>>> Then, with this, I built a lexer: >>>>> >>>>> http://jsfiddle.net/xavierm02/tUCXY/ >>>>> >>>>> Is it good or not ? >>>>> Any comment would be welcome. The only thing I'm planning on changing >>>>> is the j += newTokens.join( '' ).length; I probably need it because I >>>>> didn't store indexes properly... Or maybe because I use readTokens >>>>> that calls itself instead of a loop. >>>>> >>>>> Thanks in advance for your comments. >>>>> >>>>> On Mon, Oct 3, 2011 at 9:11 PM, Xavier MONTILLET >>>>> <[email protected]> wrote: >>>>>> Ok thank you :) >>>>>> >>>>>> On Sat, Oct 1, 2011 at 4:31 PM, Lasse Reichstein >>>>>> <[email protected]> wrote: >>>>>>> There is nothing in the complexity of '+' that mandates your Abstract >>>>>>> Syntax >>>>>>> Tree layout. It's still pure syntax at this point. >>>>>>> However, any use of the parsed syntax must behave as if the (+ a b c) >>>>>>> syntax >>>>>>> tree is equivalent to (+ (+ a b) c), so it won't buy you much, and >>>>>>> probably >>>>>>> just makes using the parsed syntax more complex. >>>>>>> If repeated use of the same operator happens a lot, and you can easily >>>>>>> handle the pairing later, by all means do make a single vairable-sized >>>>>>> node. >>>>>>> E.g., in the RegExp grammar, adjacent literal characters are really a >>>>>>> sequence of Alternatives of Terms (of Atoms), but it happens so often >>>>>>> that >>>>>>> you probably want to parse /abel.*/ as containing a single text-node >>>>>>> with >>>>>>> the text "abel". >>>>>>> Just don't optimize the abstract syntax without considering how it's >>>>>>> going >>>>>>> to be used. >>>>>>> /L >>>>>>> >>>>>>> On Sat, Oct 1, 2011 at 12:28 PM, Xavier MONTILLET >>>>>>> <[email protected]> >>>>>>> wrote: >>>>>>>> >>>>>>>> Right. I totally forgot that... >>>>>>>> So I have to keep only two operands per operator. >>>>>>>> Thank you for answering :) >>>>>>>> >>>>>>>> On Sat, Oct 1, 2011 at 12:48 AM, Poetro <[email protected]> wrote: >>>>>>>> > The + operator is not just for numbers and can have sideeffects, if >>>>>>>> > the operands have different types or the operands are not numbers or >>>>>>>> > strings (and even in that case). This makes the + operator tricky. >>>>>>>> > >>>>>>>> >>>> "boo" + 1 + 2 >>>>>>>> > "boo12" >>>>>>>> >>>> 1 + 2 + "boo" >>>>>>>> > "3boo" >>>>>>>> > >>>>>>>> >>>> var a = {toString: function () { return 1; }, valueOf: function >>>>>>>> >>>> () { >>>>>>>> >>>> return 2; }}, b = 0; a + b >>>>>>>> > 2 >>>>>>>> > >>>>>>>> > -- >>>>>>>> > Poetro >>>>>>>> > >>>>>>>> > -- >>>>>>>> > To view archived discussions from the original JSMentors Mailman >>>>>>>> > list: >>>>>>>> > http://www.mail-archive.com/[email protected]/ >>>>>>>> > >>>>>>>> > To search via a non-Google archive, visit here: >>>>>>>> > http://www.mail-archive.com/[email protected]/ >>>>>>>> > >>>>>>>> > To unsubscribe from this group, send email to >>>>>>>> > [email protected] >>>>>>>> > >>>>>>>> >>>>>>>> -- >>>>>>>> To view archived discussions from the original JSMentors Mailman list: >>>>>>>> http://www.mail-archive.com/[email protected]/ >>>>>>>> >>>>>>>> To search via a non-Google archive, visit here: >>>>>>>> http://www.mail-archive.com/[email protected]/ >>>>>>>> >>>>>>>> To unsubscribe from this group, send email to >>>>>>>> [email protected] >>>>>>> >>>>>>> -- >>>>>>> To view archived discussions from the original JSMentors Mailman list: >>>>>>> http://www.mail-archive.com/[email protected]/ >>>>>>> >>>>>>> To search via a non-Google archive, visit here: >>>>>>> http://www.mail-archive.com/[email protected]/ >>>>>>> >>>>>>> To unsubscribe from this group, send email to >>>>>>> [email protected] >>>>>>> >>>>>> >>>>> >>>> >>> >> > -- To view archived discussions from the original JSMentors Mailman list: http://www.mail-archive.com/[email protected]/ To search via a non-Google archive, visit here: http://www.mail-archive.com/[email protected]/ To unsubscribe from this group, send email to [email protected]
