| --- Log opened Sat Jun 20 00:00:29 2009 |
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| 01:51 | <@Derakon> | Argh, I really, really wish that Python descoped variables. |
| 01:51 | <@Derakon> | ...actually, this is more Python not treating every instance of a given string as a reference to a variable. |
| 01:51 | <@Derakon> | Is it too much to ask that I be allowed to have a module "seed.py" and a variable name "seed" and not have them conflict? :( |
| 01:58 | <@SmithKurosaki> | Wow, that message from Nighstar just now was special |
| 01:59 | < Alek> | it's a special-ty. :P |
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| 12:18 | | * UndeadAnno mutters. What's the amplitude value of the border frequency in a chebyshev filter? |
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| 12:32 | <@EvilDarkLord> | Google. |
| 12:36 | | * UndeadAnno throws a rock at EvilDarkLord. |
| 12:36 | <@UndeadAnno> | Don't you think I've tried that? |
| 12:43 | <@EvilDarkLord> | Mmhmm. What kind of filter is it? |
| 12:44 | <@EvilDarkLord> | Low-, band-, highpass, something else? |
| 12:49 | <@UndeadAnno> | The basic lowpass. |
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| 13:51 | < Tarinaky> | I have a string that contains "+". At some point which I've yet to locate it's getting mangled into "-0.226439". Does anyone have any insight to offer? |
| 13:51 | < Tarinaky> | If it helps I know that it corresponds to 43 as an int. |
| 13:52 | < Tarinaky> | *know '+' corresponds to 43. |
| 13:55 | < Tarinaky> | Ahah! Found the culprit. |
| 13:56 | <@Namegduf> | What was it? |
| 13:56 | < Tarinaky> | There was an '=' instead of an '=='. |
| 13:57 | < Tarinaky> | On the line my cursor was on. Blinking at me. For the past god knows how long. |
| 13:57 | <@Namegduf> | XD |
| 13:58 | < Tarinaky> | This resulted in an initialised address of memory being written into the variable -just- before printing it. |
| 13:59 | < Tarinaky> | Not that that matters. |
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| 17:28 | <@SmithKurosaki> | UndeadAnno: I have a stats book beside me, what is it you need to know about chebyshev? |
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| 17:32 | <@UndeadAnno> | SmithKurosaki: What is the amplitude value (or the 1s complement of it) at the boundary frequency? |
| 17:36 | <@SmithKurosaki> | Would getting the formaula help? |
| 17:37 | <@UndeadAnno> | Only if the formula could give me the answer shortly. |
| 17:39 | <@SmithKurosaki> | Formula: 100(1-1/k^2) |
| 17:40 | <@SmithKurosaki> | I'm sorry I couldn't find what you were exactly looking for. Good luck |
| 17:45 | | Derakon[AFK] is now known as Derakon |
| 18:24 | < Tarinaky> | I'm trying to write a math parser in C++. I've got a problem with negative numbers. I can't work out how to distinguish between a '-' as in subtraction and '-' as in negative. |
| 18:24 | < Tarinaky> | Specifically an expression like 20*(-1) trips me up. |
| 18:25 | <@Namegduf> | I think the answer is 'position', or that it will: |
| 18:25 | <@Namegduf> | 1) Be followed by a valid number thing. |
| 18:26 | <@Namegduf> | (Meaning a number, constant, bracketed expression, etc) |
| 18:26 | <@Namegduf> | 2) NOT be preceded by a "valid number thing", but by nothing or another operator. |
| 18:27 | <@Namegduf> | I'm not familiar with the proper terminology, but I hacked on the inside of a crappy C expression parser/evaluator to add implicit multiplication support and similar once. |
| 18:40 | < Tarinaky> | Thanks. I think that got it. |
| 19:02 | < simontwo> | Tarinaky, how do you write the parser; using flex? |
| 19:02 | < Tarinaky> | No. By hand. |
| 19:03 | < Tarinaky> | I couldn't find any decent documentation for flex/bison so I gave up on that. |
| 19:05 | < simontwo> | Tarinaky, and do you divide the problem into first tokenizing your expressions and then constructing an AST based on the tokens? |
| 19:06 | < Tarinaky> | I don't know what an AST is. |
| 19:06 | < Tarinaky> | I tokenise the expression then re-arrenge it into RPN. |
| 19:06 | < Tarinaky> | Also, namegduf's solution seems to have worked. |
| 19:06 | < simontwo> | abstract syntax tree. basically a tree structure that contains your expression |
| 19:07 | < simontwo> | ok |
| 19:08 | < simontwo> | Tarinaky, I'm a little influenced by having recently read in a compiler book. |
| 19:08 | < Tarinaky> | Heh. 's'okay. |
| 19:09 | < Tarinaky> | Flex/Bison sound like very nice tools but if I can't find out how to use them they aren't terribly useful >.> |
| 19:09 | < simontwo> | hehe |
| 19:14 | < simontwo> | Tarinaky, as long as you define the syntax unambiguously, it is just a matter of technique. |
| 19:17 | < simontwo> | e.g. "-" is unary when either not preceeded by a token within a parenthesis or when preceded by a binary operator token and followed by a number token. that way even 5 + -5 (without parenthesis, which you'd usually prefer in math) is unambiguous. |
| 19:17 | < simontwo> | (or 5+ - 5, for that matter) |
| 19:19 | < Tarinaky> | I'm sure but like I said. I couldn't find any resources explaining how you use them. As in, the input that the programs take. |
| 19:20 | < simontwo> | oh, well, you can make tokenizers without a lex-like tool. |
| 19:21 | < simontwo> | but yeah, I suspect you'd need a book that demonstrates flex/bison to get properly started. |
| 19:23 | <@ToxicFrog> | Tarinaky: flex: http://flex.sourceforge.net/manual/ |
| 19:24 | <@ToxicFrog> | I also highly recommend the Dragon Book, "Compilers: Principles, Techniques & Tools", for a bottom-up coverage of this sort of thing. |
| 19:24 | < simontwo> | ToxicFrog, do you know the tiger book? |
| 19:25 | < simontwo> | ("Modern Compiler Implementation in Standard ML") |
| 19:25 | < simontwo> | (by Andrew W. Appel) |
| 19:25 | <@ToxicFrog> | I don't, and indeed I don't know ML full stop. |
| 19:25 | < simontwo> | ah, hehe. |
| 19:25 | <@ToxicFrog> | I need my goddamn overloaded operators~ |
| 19:26 | <@ToxicFrog> | Tarinaky: as for bison, http://www.gnu.org/software/bison/manual/bison.html is the manual, and includes as an example how to make a calculator that does the calculations at parse time. |
| 20:03 | | * ToxicFrog does some performance tests |
| 20:03 | <@ToxicFrog> | Hand-memoized: 0.04s |
| 20:03 | <@ToxicFrog> | util.memoize()ed: 0.09 seconds |
| 20:03 | <@ToxicFrog> | No memoization: it's still running. |
| 20:04 | <@McMartin> | There are three tiger books. ML, C (which is in fact ML), and Java (which is actually a different design methodology) |
| 20:06 | <@McMartin> | The Dragon Book's treatment of flex and bison is kind of out of date, and the Tiger book - at least, Java's, which is the one I have - basically just goes "read the web page lol". |
| 20:25 | <@ToxicFrog> | I recommend the Dragon Book more for the "this is what lexing and parsing is, this is how a compiler works" stuff |
| 20:25 | <@ToxicFrog> | For specific apps, yeah, read the app's manual. |
| 20:30 | <@McMartin> | Yeah. |
| 20:31 | <@McMartin> | IME the Tiger book is better for "here are a graduated series of programming projects that end in a toy compiler" |
| 20:34 | <@SmithKurosaki> | Nice |
| 20:39 | <@McMartin> | Third edition of the Dragon Book adds a bunch of material regarding program analysis and other uses of parsers and such |
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| 23:39 | <@gnolam> | Gah. I need to do a rebuild. |
| 23:39 | <@gnolam> | Oh well. Better find something interesting to do the next 15 minutes or so. |
| 23:44 | <@gnolam> | But at least I got out of the dreaded diamond. |
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| --- Log closed Sun Jun 21 00:00:43 2009 |