diff options
| author | millaway <millaway> | 2002-07-11 20:06:52 +0000 |
|---|---|---|
| committer | millaway <millaway> | 2002-07-11 20:06:52 +0000 |
| commit | 7c3c752ffad196597dfd94ab605d8bb6690ca7a5 (patch) | |
| tree | 285945eb3f9a8976d5c16c40197c4a74e15cde3f | |
| parent | e909e7375fbd3031709bbf26b04029331c24827c (diff) | |
| download | flex-7c3c752ffad196597dfd94ab605d8bb6690ca7a5.tar.gz | |
Moved all faqs into manual -- but did not evaluate them yet.
Removed the old faq files.
| -rw-r--r-- | faq.texi | 2255 |
1 files changed, 2255 insertions, 0 deletions
@@ -69,6 +69,71 @@ * Whenever flex can not match the input it says "flex scanner jammed".:: * Why doesn't flex have non-greedy operators like perl does?:: * Memory leak - 16386 bytes allocated by malloc.:: +* How do I track the byte offset for lseek()?:: +* unnamed-faq-1:: +* unnamed-faq-16:: +* unnamed-faq-22:: +* unnamed-faq-33:: +* unnamed-faq-42:: +* unnamed-faq-43:: +* unnamed-faq-44:: +* unnamed-faq-45:: +* unnamed-faq-46:: +* unnamed-faq-47:: +* unnamed-faq-48:: +* unnamed-faq-49:: +* unnamed-faq-50:: +* unnamed-faq-51:: +* unnamed-faq-52:: +* unnamed-faq-53:: +* unnamed-faq-54:: +* unnamed-faq-55:: +* unnamed-faq-56:: +* unnamed-faq-57:: +* unnamed-faq-58:: +* unnamed-faq-59:: +* unnamed-faq-60:: +* unnamed-faq-61:: +* unnamed-faq-62:: +* unnamed-faq-63:: +* unnamed-faq-64:: +* unnamed-faq-65:: +* unnamed-faq-66:: +* unnamed-faq-67:: +* unnamed-faq-68:: +* unnamed-faq-69:: +* unnamed-faq-70:: +* unnamed-faq-71:: +* unnamed-faq-72:: +* unnamed-faq-73:: +* unnamed-faq-74:: +* unnamed-faq-75:: +* unnamed-faq-76:: +* unnamed-faq-77:: +* unnamed-faq-78:: +* unnamed-faq-79:: +* unnamed-faq-80:: +* unnamed-faq-81:: +* unnamed-faq-82:: +* unnamed-faq-83:: +* unnamed-faq-84:: +* unnamed-faq-85:: +* unnamed-faq-86:: +* unnamed-faq-87:: +* unnamed-faq-88:: +* unnamed-faq-89:: +* unnamed-faq-90:: +* unnamed-faq-91:: +* unnamed-faq-92:: +* unnamed-faq-93:: +* unnamed-faq-94:: +* unnamed-faq-95:: +* unnamed-faq-96:: +* unnamed-faq-97:: +* unnamed-faq-98:: +* unnamed-faq-99:: +* unnamed-faq-100:: +* unnamed-faq-101:: @end menu @@ -756,6 +821,10 @@ This approach also has much better error-reporting properties. @node Memory leak - 16386 bytes allocated by malloc. @unnumberedsec Memory leak - 16386 bytes allocated by malloc. +UPDATED 2002-07-10: As of flex version 2.5.9, this leak means that you did not +call yylex_destroy(). If you are using an earlier version of flex, then read +on. + The leak is about 16426 bytes. That is, (8192 * 2 + 2) for the read-buffer, and about 40 for struct yy_buffer_state (depending upon alignment). The leak is in the non-reentrant C scanner only (NOT in the reentrant scanner, NOT in the C++ @@ -778,3 +847,2189 @@ yy_init = 1; Note: yy_init is an "internal variable", and hasn't been tested in this situation. It is possible that some other globals may need resetting as well. +@node How do I track the byte offset for lseek()? +@unnumberedsec How do I track the byte offset for lseek()? + +@example +@verbatim +> We thought that it would be possible to have this number through the +> evaluation of the following expression: +> +> seek_position = (no_buffers)*YY_READ_BUF_SIZE + yy_c_buf_p - yy_current_buffer->yy_ch_buf +@end verbatim +@end example + +While this is the right ideas, it has two problems. The first is that +it's possible that flex will request less than YY_READ_BUF_SIZE during +an invocation of YY_INPUT (or that your input source will return less +even though YY_READ_BUF_SIZE bytes were requested). The second problem +is that when refilling its internal buffer, flex keeps some characters +from the previous buffer (because usually it's in the middle of a match, +and needs those characters to construct yytext for the match once it's +done). Because of this, yy_c_buf_p - yy_current_buffer->yy_ch_buf won't +be exactly the number of characters already read from the current buffer. + +An alternative solution is to count the number of characters you've matched +since starting to scan. This can be done by using YY_USER_ACTION. For +example, + + #define YY_USER_ACTION num_chars += yyleng; + +(You need to be careful to update your bookkeeping if you use yymore(), +yyless(), unput(), or input().) + +@c TODO: Evaluate this faq. +@c TODO: Evaluate this faq. +@node unnamed-faq-1 +@unnumberedsec unnamed-faq-1 +@example +@verbatim +Return-Path: mdonahue@neptune.convex.com +Received: from 130.168.1.1 by horse.ee.lbl.gov for vern (5.65/1.41) + id AA06605; Tue, 7 Jul 92 13:00:27 -0700 +Received: from neptune.convex.com by convex.convex.com (5.64/1.35) + id AA13737; Tue, 7 Jul 92 14:24:28 -0500 +Received: by neptune.convex.com (5.64/1.28) + id AA27330; Tue, 7 Jul 92 14:24:23 -0500 +From: mdonahue@neptune.convex.com (Mike Donahue) +Message-Id: <9207071924.AA27330@neptune.convex.com> +Subject: Re: Flex and Multiple Parsers +To: vern@horse.ee.lbl.gov (Vern Paxson) +Date: Tue, 7 Jul 92 14:24:22 CDT +In-Reply-To: <9207021608.AA25669@horse.ee.lbl.gov>; from "Vern Paxson" at Jul 2, 92 9:08 am +X-Mailer: ELM [version 2.3 PL11] + + + Thanks for your help, actually my solution ended up being + quite different. let me further describe my problem and + its solution to you just in case someone else has this problem. + + Basically we have a library of parsers (I think there are 15). + Most programs we write also have several of there own parsers and + call some of the routines in the library. Therefore each program + must be able to have several parsers. + + To this end I simply changed all the subroutines in the skel file + to static (just the subroutines) + + We have parsers that start parsing a file and find a section that + needs to be parsed by a library parser (the same file) therefore + the file pointer and a state must be passed into the new parser + or the file pointer and state buffers must be global declarations + (the solution we use in the previous flex and now the new one) + + Because the parsers are working on the same file declaring + yyout, yytoken, yyin, yytext, and yylen + and the other variables as static does not work, so I declared each + as and extern and local(therefore making those variable available to + all parsers) + + I.E. + + extern YYCHAR yytext; + YYCHAR yytext; + + The solution is still not yet complete, now there are compiler conflicts + with the variables that need start states (yy_init, yy_c_buf_p, ...) + and if these are static each parser will try to re_init since yy_init + will be set to 1 in every parser. The solution here was to get rid + of these declarations and make these variables global to all parsers + as well (see above). Now the user must initialize the variables, + an easy way to do this was to change yyrestart and call it after opening + a new file for reading : + +static void yyrestart( input_file ) + { + /* Below 3 added by MJD for multiple interactive parsers */ + yy_c_buf_p = (YY_CHAR *) 0; + yy_init = 1; /* whether we need to initialize */ + yy_start = 0; /* start state number */ + + /* Below 2 added by MJD for multiple interactive parsers */ + if (!input_file) return; + if (!yy_current_buffer) return; + + yy_init_buffer( yy_current_buffer, input_file ); + yy_load_buffer_state(); + + } + +I also added a routine called yyopenfile (this is actually in our +library, not in the skeleton), which opens a file, does the restart +and sets yyin to the new file pointer, returning a NULL if unsuccessful. +If this routine is used by all the parsers to open a new file then +the changes are transparent. + + +Anyways, to make a long story short that has got us going with the new +flex and if anyone else is having trouble with a similar problem +feel free to give them this solution. + +Thanks for your help and the effort you have put in providing flex, +it is an excellent tool. + +Mike + + +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-16 +@unnumberedsec unnamed-faq-16 +@example +@verbatim +To: steves@telebase.com +Subject: Re: flex C++ question +In-reply-to: Your message of Thu, 08 Dec 94 13:10:58 EST. +Date: Wed, 14 Dec 94 16:40:47 PST +From: Vern Paxson <vern> + +> We'd like to override the provided LexerInput() and LexerOutput() +> functions, but we'd like to *not* use iostreams. Instead, we'd like +> to use some of our own I/O classes. Is this possible? + +You can do this by passing the various functions nil iostream*'s, and then +dealing with your own I/O classes surreptitiously (i.e., stashing them in +special member variables). This works because the only assumption about +the lexer regarding what's done with the iostream's is that they're +ultimately passed to LexerInput and LexerOutput, which then do whatever +necessary with them. + +When the flex C++ scanning class rewrite finally happens (no date for this +in sight), then this sort of thing should become much easier. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-22 +@unnumberedsec unnamed-faq-22 +@example +@verbatim +To: matute@emf.net +Subject: Re: Question +In-reply-to: Your message of Mon, 15 May 95 11:32:12 PDT. +Date: Mon, 15 May 95 17:03:25 PDT +From: Vern Paxson <vern> + +> %x SKIP +> ... +> +> <SKIP>"endofit" { BEGIN(INITIAL); } +> <SKIP>.* ; +> <SKIP>\n lineno++; + +The simplest (but slow) fix is: + +<SKIP>"endofit" { BEGIN(INITIAL); } +<SKIP>. +<SKIP>\n lineno++; + +The better fixes all involve making the second rule match more, without +making it match "endofit" plus something else. So for example: + +<SKIP>"endofit" { BEGIN(INITIAL); } +<SKIP>.{1,7} +<SKIP>\n lineno++; + +or + +<SKIP>"endofit" { BEGIN(INITIAL); } +<SKIP>[^e\n]+ +<SKIP>. /* so you eat up e's, too */ +<SKIP>\n lineno++; + +- Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-33 +@unnumberedsec unnamed-faq-33 +@example +@verbatim +QUESTION: +When was flex born? + +Vern Paxson took over +the Software Tools lex project from Jef Poskanzer in 1982. At that point it +was written in Ratfor. Around 1987 or so, Paxson translated it into C, and +a legend was born :-). +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-42 +@unnumberedsec unnamed-faq-42 +@example +@verbatim +To: Adoram Rogel <adoram@orna.hybridge.com> +Subject: Re: Flex 2.5.2 performance questions +In-reply-to: Your message of Wed, 18 Sep 96 11:12:17 EDT. +Date: Wed, 18 Sep 96 10:51:02 PDT +From: Vern Paxson <vern> + +[Note, the most recent flex release is 2.5.4, which you can get from + ftp.ee.lbl.gov. It has bug fixes over 2.5.2 and 2.5.3.] + +> 1. Using the pattern +> ([Ff](oot)?)?[Nn](ote)?(\.)? +> instead of +> (((F|f)oot(N|n)ote)|((N|n)ote)|((N|n)\.)|((F|f)(N|n)(\.))) +> (in a very complicated flex program) caused the program to slow from +> 300K+/min to 100K/min (no other changes were done). + +These two are not equivalent. For example, the first can match "footnote." +but the second can only match "footnote". This is almost certainly the +cause in the discrepancy - the slower scanner run is matching more tokens, +and/or having to do more backing up. + +> 2. Which of these two are better: [Ff]oot or (F|f)oot ? + +From a performance point of view, they're equivalent (modulo presumably +minor effects such as memory cache hit rates; and the presence of trailing +context, see below). From a space point of view, the first is slightly +preferable. + +> 3. I have a pattern that look like this: +> pats {p1}|{p2}|{p3}|...|{p50} (50 patterns ORd) +> +> running yet another complicated program that includes the following rule: +> <snext>{and}/{no4}{bb}{pats} +> +> gets me to "too complicated - over 32,000 states"... + +I can't tell from this example whether the trailing context is variable-length +or fixed-length (it could be the latter if {and} is fixed-length). If it's +variable length, which flex -p will tell you, then this reflects a basic +performance problem, and if you can eliminate it by restructuring your +scanner, you will see significant improvement. + +> so I divided {pats} to {pats1}, {pats2},..., {pats5} each consists of about +> 10 patterns and changed the rule to be 5 rules. +> This did compile, but what is the rule of thumb here ? + +The rule is to avoid trailing context other than fixed-length, in which for +a/b, either the 'a' pattern or the 'b' pattern have a fixed length. Use +of the '|' operator automatically makes the pattern variable length, so in +this case '[Ff]oot' is preferred to '(F|f)oot'. + +> 4. I changed a rule that looked like this: +> <snext8>{and}{bb}/{ROMAN}[^A-Za-z] { BEGIN... +> +> to the next 2 rules: +> <snext8>{and}{bb}/{ROMAN}[A-Za-z] { ECHO;} +> <snext8>{and}{bb}/{ROMAN} { BEGIN... +> +> Again, I understand the using [^...] will cause a great performance loss + +Actually, it doesn't cause any sort of performance loss. It's a surprising +fact about regular expressions that they always match in linear time +regardless of how complex they are. + +> but are there any specific rules about it ? + +See the "Performance Considerations" section of the man page, and also +the example in MISC/fastwc/. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-43 +@unnumberedsec unnamed-faq-43 +@example +@verbatim +To: Adoram Rogel <adoram@hybridge.com> +Subject: Re: Flex 2.5.2 performance questions +In-reply-to: Your message of Thu, 19 Sep 96 10:16:04 EDT. +Date: Thu, 19 Sep 96 09:58:00 PDT +From: Vern Paxson <vern> + +> a lot about the backing up problem. +> I believe that there lies my biggest problem, and I'll try to improve +> it. + +Since you have variable trailing context, this is a bigger performance +problem. Fixing it is usually easier than fixing backing up, which in a +complicated scanner (yours seems to fit the bill) can be extremely +difficult to do correctly. + +You also don't mention what flags you are using for your scanner. +-f makes a large speed difference, and -Cfe buys you nearly as much +speed but the resulting scanner is considerably smaller. + +> I have an | operator in {and} and in {pats} so both of them are variable +> length. + +-p should have reported this. + +> Is changing one of them to fixed-length is enough ? + +Yes. + +> Is it possible to change the 32,000 states limit ? + +Yes. I've appended instructions on how. Before you make this change, +though, you should think about whether there are ways to fundamentally +simplify your scanner - those are certainly preferable! + + Vern + + +To increase the 32K limit (on a machine with 32 bit integers), you increase +the magnitude of the following in flexdef.h: + + #define JAMSTATE -32766 /* marks a reference to the state that always jams */ + #define MAXIMUM_MNS 31999 + #define BAD_SUBSCRIPT -32767 + #define MAX_SHORT 32700 + +Adding a 0 or two after each should do the trick. +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-44 +@unnumberedsec unnamed-faq-44 +@example +@verbatim +To: Heeman_Lee@hp.com +Subject: Re: flex - multi-byte support? +In-reply-to: Your message of Thu, 03 Oct 1996 17:24:04 PDT. +Date: Fri, 04 Oct 1996 11:42:18 PDT +From: Vern Paxson <vern> + +> I assume as long as my *.l file defines the +> range of expected character code values (in octal format), flex will +> scan the file and read multi-byte characters correctly. But I have no +> confidence in this assumption. + +Your lack of confidence is justified - this won't work. + +Flex has in it a widespread assumption that the input is processed +one byte at a time. Fixing this is on the to-do list, but is involved, +so it won't happen any time soon. In the interim, the best I can suggest +(unless you want to try fixing it yourself) is to write your rules in +terms of pairs of bytes, using definitions in the first section: + + X \xfe\xc2 + ... + %% + foo{X}bar found_foo_fe_c2_bar(); + +etc. Definitely a pain - sorry about that. + +By the way, the email address you used for me is ancient, indicating you +have a very old version of flex. You can get the most recent, 2.5.4, from +ftp.ee.lbl.gov. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-45 +@unnumberedsec unnamed-faq-45 +@example +@verbatim +To: moleary@primus.com +Subject: Re: Flex / Unicode compatibility question +In-reply-to: Your message of Tue, 22 Oct 1996 10:15:42 PDT. +Date: Tue, 22 Oct 1996 11:06:13 PDT +From: Vern Paxson <vern> + +Unfortunately flex at the moment has a widespread assumption within it +that characters are processed 8 bits at a time. I don't see any easy +fix for this (other than writing your rules in terms of double characters - +a pain). I also don't know of a wider lex, though you might try surfing +the Plan 9 stuff because I know it's a Unicode system, and also the PCCT +toolkit (try searching say Alta Vista for "Purdue Compiler Construction +Toolkit"). + +Fixing flex to handle wider characters is on the long-term to-do list. +But since flex is a strictly spare-time project these days, this probably +won't happen for quite a while, unless someone else does it first. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-46 +@unnumberedsec unnamed-faq-46 +@example +@verbatim +To: Johan Linde <jl@theophys.kth.se> +Subject: Re: translation of flex +In-reply-to: Your message of Sun, 10 Nov 1996 09:16:36 PST. +Date: Mon, 11 Nov 1996 10:33:50 PST +From: Vern Paxson <vern> + +> I'm working for the Swedish team translating GNU program, and I'm currently +> working with flex. I have a few questions about some of the messages which +> I hope you can answer. + +All of the things you're wondering about, by the way, concerning flex +internals - probably the only person who understands what they mean in +English is me! So I wouldn't worry too much about getting them right. +That said ... + +> #: main.c:545 +> msgid " %d protos created\n" +> +> Does proto mean prototype? + +Yes - prototypes of state compression tables. + +> #: main.c:539 +> msgid " %d/%d (peak %d) template nxt-chk entries created\n" +> +> Here I'm mainly puzzled by 'nxt-chk'. I guess it means 'next-check'. (?) +> However, 'template next-check entries' doesn't make much sense to me. To be +> able to find a good translation I need to know a little bit more about it. + +There is a scheme in the Aho/Sethi/Ullman compiler book for compressing +scanner tables. It involves creating two pairs of tables. The first has +"base" and "default" entries, the second has "next" and "check" entries. +The "base" entry is indexed by the current state and yields an index into +the next/check table. The "default" entry gives what to do if the state +transition isn't found in next/check. The "next" entry gives the next +state to enter, but only if the "check" entry verifies that this entry is +correct for the current state. Flex creates templates of series of +next/check entries and then encodes differences from these templates as a +way to compress the tables. + +> #: main.c:533 +> msgid " %d/%d base-def entries created\n" +> +> The same problem here for 'base-def'. + +See above. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-47 +@unnumberedsec unnamed-faq-47 +@example +@verbatim +To: Xinying Li <xli@npac.syr.edu> +Subject: Re: FLEX ? +In-reply-to: Your message of Wed, 13 Nov 1996 17:28:38 PST. +Date: Wed, 13 Nov 1996 19:51:54 PST +From: Vern Paxson <vern> + +> "unput()" them to input flow, question occurs. If I do this after I scan +> a carriage, the variable "yy_current_buffer->yy_at_bol" is changed. That +> means the carriage flag has gone. + +You can control this by calling yy_set_bol(). It's described in the manual. + +> And if in pre-reading it goes to the end of file, is anything done +> to control the end of curren buffer and end of file? + +No, there's no way to put back an end-of-file. + +> By the way I am using flex 2.5.2 and using the "-l". + +The latest release is 2.5.4, by the way. It fixes some bugs in 2.5.2 and +2.5.3. You can get it from ftp.ee.lbl.gov. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-48 +@unnumberedsec unnamed-faq-48 +@example +@verbatim +To: Alain.ISSARD@st.com +Subject: Re: Start condition with FLEX +In-reply-to: Your message of Mon, 18 Nov 1996 09:45:02 PST. +Date: Mon, 18 Nov 1996 10:41:34 PST +From: Vern Paxson <vern> + +> I am not able to use the start condition scope and to use the | (OR) with +> rules having start conditions. + +The problem is that if you use '|' as a regular expression operator, for +example "a|b" meaning "match either 'a' or 'b'", then it must *not* have +any blanks around it. If you instead want the special '|' *action* (which +from your scanner appears to be the case), which is a way of giving two +different rules the same action: + + foo | + bar matched_foo_or_bar(); + +then '|' *must* be separated from the first rule by whitespace and *must* +be followed by a new line. You *cannot* write it as: + + foo | bar matched_foo_or_bar(); + +even though you might think you could because yacc supports this syntax. +The reason for this unfortunately incompatibility is historical, but it's +unlikely to be changed. + +Your problems with start condition scope are simply due to syntax errors +from your use of '|' later confusing flex. + +Let me know if you still have problems. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-49 +@unnumberedsec unnamed-faq-49 +@example +@verbatim +To: Gregory Margo <gmargo@newton.vip.best.com> +Subject: Re: flex-2.5.3 bug report +In-reply-to: Your message of Sat, 23 Nov 1996 16:50:09 PST. +Date: Sat, 23 Nov 1996 17:07:32 PST +From: Vern Paxson <vern> + +> Enclosed is a lex file that "real" lex will process, but I cannot get +> flex to process it. Could you try it and maybe point me in the right direction? + +Your problem is that some of the definitions in the scanner use the '/' +trailing context operator, and have it enclosed in ()'s. Flex does not +allow this operator to be enclosed in ()'s because doing so allows undefined +regular expressions such as "(a/b)+". So the solution is to remove the +parentheses. Note that you must also be building the scanner with the -l +option for AT&T lex compatibility. Without this option, flex automatically +encloses the definitions in parentheses. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-50 +@unnumberedsec unnamed-faq-50 +@example +@verbatim +To: Thomas Hadig <hadig@toots.physik.rwth-aachen.de> +Subject: Re: Flex Bug ? +In-reply-to: Your message of Tue, 26 Nov 1996 14:35:01 PST. +Date: Tue, 26 Nov 1996 11:15:05 PST +From: Vern Paxson <vern> + +> In my lexer code, i have the line : +> ^\*.* { } +> +> Thus all lines starting with an astrix (*) are comment lines. +> This does not work ! + +I can't get this problem to reproduce - it works fine for me. Note +though that if what you have is slightly different: + + COMMENT ^\*.* + %% + {COMMENT} { } + +then it won't work, because flex pushes back macro definitions enclosed +in ()'s, so the rule becomes + + (^\*.*) { } + +and now that the '^' operator is not at the immediate beginning of the +line, it's interpreted as just a regular character. You can avoid this +behavior by using the "-l" lex-compatibility flag, or "%option lex-compat". + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-51 +@unnumberedsec unnamed-faq-51 +@example +@verbatim +To: Adoram Rogel <adoram@hybridge.com> +Subject: Re: Flex 2.5.4 BOF ??? +In-reply-to: Your message of Tue, 26 Nov 1996 16:10:41 PST. +Date: Wed, 27 Nov 1996 10:56:25 PST +From: Vern Paxson <vern> + +> Organization(s)?/[a-z] +> +> This matched "Organizations" (looking in debug mode, the trailing s +> was matched with trailing context instead of the optional (s) in the +> end of the word. + +That should only happen with lex. Flex can properly match this pattern. +(That might be what you're saying, I'm just not sure.) + +> Is there a way to avoid this dangerous trailing context problem ? + +Unfortunately, there's no easy way. On the other hand, I don't see why +it should be a problem. Lex's matching is clearly wrong, and I'd hope +that usually the intent remains the same as expressed with the pattern, +so flex's matching will be correct. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-52 +@unnumberedsec unnamed-faq-52 +@example +@verbatim +To: Cameron MacKinnon <mackin@interlog.com> +Subject: Re: Flex documentation bug +In-reply-to: Your message of Mon, 02 Dec 1996 00:07:08 PST. +Date: Sun, 01 Dec 1996 22:29:39 PST +From: Vern Paxson <vern> + +> I'm not sure how or where to submit bug reports (documentation or +> otherwise) for the GNU project stuff ... + +Well, strictly speaking flex isn't part of the GNU project. They just +distribute it because no one's written a decent GPL'd lex replacement. +So you should send bugs directly to me. Those sent to the GNU folks +sometimes find there way to me, but some may drop between the cracks. + +> In GNU Info, under the section 'Start Conditions', and also in the man +> page (mine's dated April '95) is a nice little snippet showing how to +> parse C quoted strings into a buffer, defined to be MAX_STR_CONST in +> size. Unfortunately, no overflow checking is ever done ... + +This is already mentioned in the manual: + + Finally, here's an example of how to match C-style quoted + strings using exclusive start conditions, including expanded + escape sequences (but not including checking for a string + that's too long): + +The reason for not doing the overflow checking is that it will needlessly +clutter up an example whose main purpose is just to demonstrate how to +use flex. + +The latest release is 2.5.4, by the way, available from ftp.ee.lbl.gov. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-53 +@unnumberedsec unnamed-faq-53 +@example +@verbatim +To: tsv@cs.UManitoba.CA +Subject: Re: Flex (reg).. +In-reply-to: Your message of Thu, 06 Mar 1997 23:50:16 PST. +Date: Thu, 06 Mar 1997 15:54:19 PST +From: Vern Paxson <vern> + +> [:alpha:] ([:alnum:] | \\_)* + +If your rule really has embedded blanks as shown above, then it won't +work, as the first blank delimits the rule from the action. (It wouldn't +even compile ...) You need instead: + +[:alpha:]([:alnum:]|\\_)* + +and that should work fine - there's no restriction on what can go inside +of ()'s except for the trailing context operator, '/'. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-54 +@unnumberedsec unnamed-faq-54 +@example +@verbatim +To: "Mike Stolnicki" <mstolnic@ford.com> +Subject: Re: FLEX help +In-reply-to: Your message of Fri, 30 May 1997 13:33:27 PDT. +Date: Fri, 30 May 1997 10:46:35 PDT +From: Vern Paxson <vern> + +> We'd like to add "if-then-else", "while", and "for" statements to our +> language ... +> We've investigated many possible solutions. The one solution that seems +> the most reasonable involves knowing the position of a TOKEN in yyin. + +I strongly advise you to instead build a parse tree (abstract syntax tree) +and loop over that instead. You'll find this has major benefits in keeping +your interpreter simple and extensible. + +That said, the functionality you mention for get_position and set_position +have been on the to-do list for a while. As flex is a purely spare-time +project for me, no guarantees when this will be added (in particular, it +for sure won't be for many months to come). + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-55 +@unnumberedsec unnamed-faq-55 +@example +@verbatim +To: Colin Paul Adams <colin@colina.demon.co.uk> +Subject: Re: Flex C++ classes and Bison +In-reply-to: Your message of 09 Aug 1997 17:11:41 PDT. +Date: Fri, 15 Aug 1997 10:48:19 PDT +From: Vern Paxson <vern> + +> #define YY_DECL int yylex (YYSTYPE *lvalp, struct parser_control +> *parm) +> +> I have been trying to get this to work as a C++ scanner, but it does +> not appear to be possible (warning that it matches no declarations in +> yyFlexLexer, or something like that). +> +> Is this supposed to be possible, or is it being worked on (I DID +> notice the comment that scanner classes are still experimental, so I'm +> not too hopeful)? + +What you need to do is derive a subclass from yyFlexLexer that provides +the above yylex() method, squirrels away lvalp and parm into member +variables, and then invokes yyFlexLexer::yylex() to do the regular scanning. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-56 +@unnumberedsec unnamed-faq-56 +@example +@verbatim +To: Mikael.Latvala@lmf.ericsson.se +Subject: Re: Possible mistake in Flex v2.5 document +In-reply-to: Your message of Fri, 05 Sep 1997 16:07:24 PDT. +Date: Fri, 05 Sep 1997 10:01:54 PDT +From: Vern Paxson <vern> + +> In that example you show how to count comment lines when using +> C style /* ... */ comments. My question is, shouldn't you take into +> account a scenario where end of a comment marker occurs inside +> character or string literals? + +The scanner certainly needs to also scan character and string literals. +However it does that (there's an example in the man page for strings), the +lexer will recognize the beginning of the literal before it runs across the +embedded "/*". Consequently, it will finish scanning the literal before it +even considers the possibility of matching "/*". + +Example: + + '([^']*|{ESCAPE_SEQUENCE})' + +will match all the text between the ''s (inclusive). So the lexer +considers this as a token beginning at the first ', and doesn't even +attempt to match other tokens inside it. + +I thinnk this subtlety is not worth putting in the manual, as I suspect +it would confuse more people than it would enlighten. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-57 +@unnumberedsec unnamed-faq-57 +@example +@verbatim +To: "Marty Leisner" <leisner@sdsp.mc.xerox.com> +Subject: Re: flex limitations +In-reply-to: Your message of Sat, 06 Sep 1997 11:27:21 PDT. +Date: Mon, 08 Sep 1997 11:38:08 PDT +From: Vern Paxson <vern> + +> %% +> [a-zA-Z]+ /* skip a line */ +> { printf("got %s\n", yytext); } +> %% + +What version of flex are you using? If I feed this to 2.5.4, it complains: + + "bug.l", line 5: EOF encountered inside an action + "bug.l", line 5: unrecognized rule + "bug.l", line 5: fatal parse error + +Not the world's greatest error message, but it manages to flag the problem. + +(With the introduction of start condition scopes, flex can't accommodate +an action on a separate line, since it's ambiguous with an indented rule.) + +You can get 2.5.4 from ftp.ee.lbl.gov. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-58 +@unnumberedsec unnamed-faq-58 +@example +@verbatim +To: uocarroll@deagostini.co.uk (Ultan O'Carroll) +Subject: Re: Flex repositries +In-reply-to: Your message of Fri, 12 Sep 1997 15:02:28 PDT. +Date: Fri, 12 Sep 1997 10:31:50 PDT +From: Vern Paxson <vern> + +> before I start beavering away I wonder if you know of any +> place/libraries for flex +> desciption files that might already do this or give me a head start ? + +Unfortunately, no, I don't. You might try asking on comp.compilers. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-59 +@unnumberedsec unnamed-faq-59 +@example +@verbatim +To: Adoram Rogel <adoram@hybridge.com> +Subject: Re: Conditional compiling in the definitions section +In-reply-to: Your message of Thu, 25 Sep 1997 11:22:42 PDT. +Date: Thu, 25 Sep 1997 10:56:31 PDT +From: Vern Paxson <vern> + +> I'm trying to combine two large lex files that now differ only in +> about 10 lines in the definitions section. +> I would like to have something like this: +> #ifdef FFF +> it \<IT\> +> #else +> it \<I\> +> #endif +> +> Now, I can't add states for these, as I have already too many states +> and the program is very complicated, and I won't be able to handle +> 10 or 20 more states. +> +> Any trick to do this ? + +You might try using m4, or the C preprocessor plus a sed script to +clean up the result (strip out the #line's). + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-60 +@unnumberedsec unnamed-faq-60 +@example +@verbatim +To: Steve Antoch <SteveAn@visio.com> +Subject: Re: lex and yacc grammars +In-reply-to: Your message of Mon, 17 Nov 1997 15:31:25 PST. +Date: Mon, 17 Nov 1997 15:27:01 PST +From: Vern Paxson <vern> + +> Would you happen to know where I can find grammars for lex and yacc? + +The flex sources have a grammar for (f)lex. Dunno about yacc, + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-61 +@unnumberedsec unnamed-faq-61 +@example +@verbatim +To: Bryan Housel <bryan@drawcomp.com> +Subject: Re: Question about Flex v2.5 +In-reply-to: Your message of Tue, 11 Nov 1997 21:30:23 PST. +Date: Mon, 17 Nov 1997 17:12:21 PST +From: Vern Paxson <vern> + +> It prints one of those "end of buffer.." messages for each character in the +> token... + +This will happen if your LexerInput() function returns only one character +at a time, which can happen either if you're scanner is "interactive", or +if the streams library on your platform always returns 1 for yyin->gcount(). + +Solution: override LexerInput() with a version that returns whole buffers. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-62 +@unnumberedsec unnamed-faq-62 +@example +@verbatim +To: Georg.Rehm@CL-KI.Uni-Osnabrueck.DE +Subject: Re: Flex maximums +In-reply-to: Your message of Mon, 17 Nov 1997 17:16:06 PST. +Date: Mon, 17 Nov 1997 17:16:15 PST +From: Vern Paxson <vern> + +> I took a quick look into the flex-sources and altered some #defines in +> flexdefs.h: +> +> #define INITIAL_MNS 64000 +> #define MNS_INCREMENT 1024000 +> #define MAXIMUM_MNS 64000 + +The things to fix are to add a couple of zeroes to: + + #define JAMSTATE -32766 /* marks a reference to the state that always jams */ + #define MAXIMUM_MNS 31999 + #define BAD_SUBSCRIPT -32767 + #define MAX_SHORT 32700 + +and, if you get complaints about too many rules, make the following change too: + + #define YY_TRAILING_MASK 0x200000 + #define YY_TRAILING_HEAD_MASK 0x400000 + +- Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-63 +@unnumberedsec unnamed-faq-63 +@example +@verbatim +To: jimmey@lexis-nexis.com (Jimmey Todd) +Subject: Re: FLEX question regarding istream vs ifstream +In-reply-to: Your message of Mon, 08 Dec 1997 15:54:15 PST. +Date: Mon, 15 Dec 1997 13:21:35 PST +From: Vern Paxson <vern> + +> stdin_handle = YY_CURRENT_BUFFER; +> ifstream fin( "aFile" ); +> yy_switch_to_buffer( yy_create_buffer( fin, YY_BUF_SIZE ) ); +> +> What I'm wanting to do, is pass the contents of a file thru one set +> of rules and then pass stdin thru another set... It works great if, I +> don't use the C++ classes. But since everything else that I'm doing is +> in C++, I thought I'd be consistent. +> +> The problem is that 'yy_create_buffer' is expecting an istream* as it's +> first argument (as stated in the man page). However, fin is a ifstream +> object. Any ideas on what I might be doing wrong? Any help would be +> appreciated. Thanks!! + +You need to pass &fin, to turn it into an ifstream* instead of an ifstream. +Then its type will be compatible with the expected istream*, because ifstream +is derived from istream. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-64 +@unnumberedsec unnamed-faq-64 +@example +@verbatim +To: Enda Fadian <fadiane@piercom.ie> +Subject: Re: Question related to Flex man page? +In-reply-to: Your message of Tue, 16 Dec 1997 15:17:34 PST. +Date: Tue, 16 Dec 1997 14:17:09 PST +From: Vern Paxson <vern> + +> Can you explain to me what is ment by a long-jump in relation to flex? + +Using the longjmp() function while inside yylex() or a routine called by it. + +> what is the flex activation frame. + +Just yylex()'s stack frame. + +> As far as I can see yyrestart will bring me back to the sart of the input +> file and using flex++ isnot really an option! + +No, yyrestart() doesn't imply a rewind, even though its name might sound +like it does. It tells the scanner to flush its internal buffers and +start reading from the given file at its present location. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-65 +@unnumberedsec unnamed-faq-65 +@example +@verbatim +To: hassan@larc.info.uqam.ca (Hassan Alaoui) +Subject: Re: Need urgent Help +In-reply-to: Your message of Sat, 20 Dec 1997 19:38:19 PST. +Date: Sun, 21 Dec 1997 21:30:46 PST +From: Vern Paxson <vern> + +> /usr/lib/yaccpar: In function `int yyparse()': +> /usr/lib/yaccpar:184: warning: implicit declaration of function `int yylex(...)' +> +> ld: Undefined symbol +> _yylex +> _yyparse +> _yyin + +This is a known problem with Solaris C++ (and/or Solaris yacc). I believe +the fix is to explicitly insert some 'extern "C"' statements for the +corresponding routines/symbols. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-66 +@unnumberedsec unnamed-faq-66 +@example +@verbatim +To: mc0307@mclink.it +Cc: gnu@prep.ai.mit.edu +Subject: Re: [mc0307@mclink.it: Help request] +In-reply-to: Your message of Fri, 12 Dec 1997 17:57:29 PST. +Date: Sun, 21 Dec 1997 22:33:37 PST +From: Vern Paxson <vern> + +> This is my definition for float and integer types: +> . . . +> NZD [1-9] +> ... +> I've tested my program on other lex version (on UNIX Sun Solaris an HP +> UNIX) and it work well, so I think that my definitions are correct. +> There are any differences between Lex and Flex? + +There are indeed differences, as discussed in the man page. The one +you are probably running into is that when flex expands a name definition, +it puts parentheses around the expansion, while lex does not. There's +an example in the man page of how this can lead to different matching. +Flex's behavior complies with the POSIX standard (or at least with the +last POSIX draft I saw). + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-67 +@unnumberedsec unnamed-faq-67 +@example +@verbatim +To: hassan@larc.info.uqam.ca (Hassan Alaoui) +Subject: Re: Thanks +In-reply-to: Your message of Mon, 22 Dec 1997 16:06:35 PST. +Date: Mon, 22 Dec 1997 14:35:05 PST +From: Vern Paxson <vern> + +> Thank you very much for your help. I compile and link well with C++ while +> declaring 'yylex ...' extern, But a little problem remains. I get a +> segmentation default when executing ( I linked with lfl library) while it +> works well when using LEX instead of flex. Do you have some ideas about the +> reason for this ? + +The one possible reason for this that comes to mind is if you've defined +yytext as "extern char yytext[]" (which is what lex uses) instead of +"extern char *yytext" (which is what flex uses). If it's not that, then +I'm afraid I don't know what the problem might be. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-68 +@unnumberedsec unnamed-faq-68 +@example +@verbatim +To: "Bart Niswonger" <NISWONGR@almaden.ibm.com> +Subject: Re: flex 2.5: c++ scanners & start conditions +In-reply-to: Your message of Tue, 06 Jan 1998 10:34:21 PST. +Date: Tue, 06 Jan 1998 19:19:30 PST +From: Vern Paxson <vern> + +> The problem is that when I do this (using %option c++) start +> conditions seem to not apply. + +The BEGIN macro modifies the yy_start variable. For C scanners, this +is a static with scope visible through the whole file. For C++ scanners, +it's a member variable, so it only has visible scope within a member +function. Your lexbegin() routine is not a member function when you +build a C++ scanner, so it's not modifying the correct yy_start. The +diagnostic that indicates this is that you found you needed to add +a declaration of yy_start in order to get your scanner to compile when +using C++; instead, the correct fix is to make lexbegin() a member +function (by deriving from yyFlexLexer). + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-69 +@unnumberedsec unnamed-faq-69 +@example +@verbatim +To: "Boris Zinin" <boris@ippe.rssi.ru> +Subject: Re: current position in flex buffer +In-reply-to: Your message of Mon, 12 Jan 1998 18:58:23 PST. +Date: Mon, 12 Jan 1998 12:03:15 PST +From: Vern Paxson <vern> + +> The problem is how to determine the current position in flex active +> buffer when a rule is matched.... + +You will need to keep track of this explicitly, such as by redefining +YY_USER_ACTION to count the number of characters matched. + +The latest flex release, by the way, is 2.5.4, available from ftp.ee.lbl.gov. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-70 +@unnumberedsec unnamed-faq-70 +@example +@verbatim +To: Bik.Dhaliwal@bis.org +Subject: Re: Flex question +In-reply-to: Your message of Mon, 26 Jan 1998 13:05:35 PST. +Date: Tue, 27 Jan 1998 22:41:52 PST +From: Vern Paxson <vern> + +> That requirement involves knowing +> the character position at which a particular token was matched +> in the lexer. + +The way you have to do this is by explicitly keeping track of where +you are in the file, by counting the number of characters scanned +for each token (available in yyleng). It may prove convenient to +do this by redefining YY_USER_ACTION, as described in the manual. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-71 +@unnumberedsec unnamed-faq-71 +@example +@verbatim +To: Vladimir Alexiev <vladimir@cs.ualberta.ca> +Subject: Re: flex: how to control start condition from parser? +In-reply-to: Your message of Mon, 26 Jan 1998 05:50:16 PST. +Date: Tue, 27 Jan 1998 22:45:37 PST +From: Vern Paxson <vern> + +> It seems useful for the parser to be able to tell the lexer about such +> context dependencies, because then they don't have to be limited to +> local or sequential context. + +One way to do this is to have the parser call a stub routine that's +included in the scanner's .l file, and consequently that has access ot +BEGIN. The only ugliness is that the parser can't pass in the state +it wants, because those aren't visible - but if you don't have many +such states, then using a different set of names doesn't seem like +to much of a burden. + +While generating a .h file like you suggests is certainly cleaner, +flex development has come to a virtual stand-still :-(, so a workaround +like the above is much more pragmatic than waiting for a new feature. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-72 +@unnumberedsec unnamed-faq-72 +@example +@verbatim +To: Barbara Denny <denny@3com.com> +Subject: Re: freebsd flex bug? +In-reply-to: Your message of Fri, 30 Jan 1998 12:00:43 PST. +Date: Fri, 30 Jan 1998 12:42:32 PST +From: Vern Paxson <vern> + +> lex.yy.c:1996: parse error before `=' + +This is the key, identifying this error. (It may help to pinpoint +it by using flex -L, so it doesn't generate #line directives in its +output.) I will bet you heavy money that you have a start condition +name that is also a variable name, or something like that; flex spits +out #define's for each start condition name, mapping them to a number, +so you can wind up with: + + %x foo + %% + ... + %% + void bar() + { + int foo = 3; + } + +and the penultimate will turn into "int 1 = 3" after C preprocessing, +since flex will put "#define foo 1" in the generated scanner. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-73 +@unnumberedsec unnamed-faq-73 +@example +@verbatim +To: Maurice Petrie <mpetrie@infoscigroup.com> +Subject: Re: Lost flex .l file +In-reply-to: Your message of Mon, 02 Feb 1998 14:10:01 PST. +Date: Mon, 02 Feb 1998 11:15:12 PST +From: Vern Paxson <vern> + +> I am curious as to +> whether there is a simple way to backtrack from the generated source to +> reproduce the lost list of tokens we are searching on. + +In theory, it's straight-forward to go from the DFA representation +back to a regular-expression representation - the two are isomorphic. +In practice, a huge headache, because you have to unpack all the tables +back into a single DFA representation, and then write a program to munch +on that and translate it into an RE. + +Sorry for the less-than-happy news ... + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-74 +@unnumberedsec unnamed-faq-74 +@example +@verbatim +To: jimmey@lexis-nexis.com (Jimmey Todd) +Subject: Re: Flex performance question +In-reply-to: Your message of Thu, 19 Feb 1998 11:01:17 PST. +Date: Thu, 19 Feb 1998 08:48:51 PST +From: Vern Paxson <vern> + +> What I have found, is that the smaller the data chunk, the faster the +> program executes. This is the opposite of what I expected. Should this be +> happening this way? + +This is exactly what will happen if your input file has embedded NULs. +From the man page: + + A final note: flex is slow when matching NUL's, particularly + when a token contains multiple NUL's. It's best to write + rules which match short amounts of text if it's anticipated + that the text will often include NUL's. + +So that's the first thing to look for. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-75 +@unnumberedsec unnamed-faq-75 +@example +@verbatim +To: jimmey@lexis-nexis.com (Jimmey Todd) +Subject: Re: Flex performance question +In-reply-to: Your message of Thu, 19 Feb 1998 11:01:17 PST. +Date: Thu, 19 Feb 1998 15:42:25 PST +From: Vern Paxson <vern> + +So there are several problems. + +First, to go fast, you want to match as much text as possible, which +your scanners don't in the case that what they're scanning is *not* +a <RN> tag. So you want a rule like: + + [^<]+ + +Second, C++ scanners are particularly slow if they're interactive, +which they are by default. Using -B speeds it up by a factor of 3-4 +on my workstation. + +Third, C++ scanners that use the istream interface are slow, because +of how poorly implemented istream's are. I built two versions of +the following scanner: + + %% + .*\n + .* + %% + +and the C version inhales a 2.5MB file on my workstation in 0.8 seconds. +The C++ istream version, using -B, takes 3.8 seconds. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-76 +@unnumberedsec unnamed-faq-76 +@example +@verbatim +To: "Frescatore, David (CRD, TAD)" <frescatore@exc01crdge.crd.ge.com> +Subject: Re: FLEX 2.5 & THE YEAR 2000 +In-reply-to: Your message of Wed, 03 Jun 1998 11:26:22 PDT. +Date: Wed, 03 Jun 1998 10:22:26 PDT +From: Vern Paxson <vern> + +> I am researching the Y2K problem with General Electric R&D +> and need to know if there are any known issues concerning +> the above mentioned software and Y2K regardless of version. + +There shouldn't be, all it ever does with the date is ask the system +for it and then print it out. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-77 +@unnumberedsec unnamed-faq-77 +@example +@verbatim +To: "Hans Dermot Doran" <htd@ibhdoran.com> +Subject: Re: flex problem +In-reply-to: Your message of Wed, 15 Jul 1998 21:30:13 PDT. +Date: Tue, 21 Jul 1998 14:23:34 PDT +From: Vern Paxson <vern> + +> To overcome this, I gets() the stdin into a string and lex the string. The +> string is lexed OK except that the end of string isn't lexed properly +> (yy_scan_string()), that is the lexer dosn't recognise the end of string. + +Flex doesn't contain mechanisms for recognizing buffer endpoints. But if +you use fgets instead (which you should anyway, to protect against buffer +overflows), then the final \n will be preserved in the string, and you can +scan that in order to find the end of the string. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-78 +@unnumberedsec unnamed-faq-78 +@example +@verbatim +To: soumen@almaden.ibm.com +Subject: Re: Flex++ 2.5.3 instance member vs. static member +In-reply-to: Your message of Mon, 27 Jul 1998 02:10:04 PDT. +Date: Tue, 28 Jul 1998 01:10:34 PDT +From: Vern Paxson <vern> + +> %{ +> int mylineno = 0; +> %} +> ws [ \t]+ +> alpha [A-Za-z] +> dig [0-9] +> %% +> +> Now you'd expect mylineno to be a member of each instance of class +> yyFlexLexer, but is this the case? A look at the lex.yy.cc file seems to +> indicate otherwise; unless I am missing something the declaration of +> mylineno seems to be outside any class scope. +> +> How will this work if I want to run a multi-threaded application with each +> thread creating a FlexLexer instance? + +Derive your own subclass and make mylineno a member variable of it. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-79 +@unnumberedsec unnamed-faq-79 +@example +@verbatim +To: Adoram Rogel <adoram@hybridge.com> +Subject: Re: More than 32K states change hangs +In-reply-to: Your message of Tue, 04 Aug 1998 16:55:39 PDT. +Date: Tue, 04 Aug 1998 22:28:45 PDT +From: Vern Paxson <vern> + +> Vern Paxson, +> +> I followed your advice, posted on Usenet bu you, and emailed to me +> personally by you, on how to overcome the 32K states limit. I'm running +> on Linux machines. +> I took the full source of version 2.5.4 and did the following changes in +> flexdef.h: +> #define JAMSTATE -327660 +> #define MAXIMUM_MNS 319990 +> #define BAD_SUBSCRIPT -327670 +> #define MAX_SHORT 327000 +> +> and compiled. +> All looked fine, including check and bigcheck, so I installed. + +Hmmm, you shouldn't increase MAX_SHORT, though looking through my email +archives I see that I did indeed recommend doing so. Try setting it back +to 32700; that should suffice that you no longer need -Ca. If it still +hangs, then the interesting question is - where? + +> Compiling the same hanged program with a out-of-the-box (RedHat 4.2 +> distribution of Linux) +> flex 2.5.4 binary works. + +Since Linux comes with source code, you should diff it against what +you have to see what problems they missed. + +> Should I always compile with the -Ca option now ? even short and simple +> filters ? + +No, definitely not. It's meant to be for those situations where you +absolutely must squeeze every last cycle out of your scanner. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-80 +@unnumberedsec unnamed-faq-80 +@example +@verbatim +To: "Schmackpfeffer, Craig" <Craig.Schmackpfeffer@usa.xerox.com> +Subject: Re: flex output for static code portion +In-reply-to: Your message of Tue, 11 Aug 1998 11:55:30 PDT. +Date: Mon, 17 Aug 1998 23:57:42 PDT +From: Vern Paxson <vern> + +> I would like to use flex under the hood to generate a binary file +> containing the data structures that control the parse. + +This has been on the wish-list for a long time. In principle it's +straight-forward - you redirect mkdata() et al's I/O to another file, +and modify the skeleton to have a start-up function that slurps these +into dynamic arrays. The concerns are (1) the scanner generation code +is hairy and full of corner cases, so it's easy to get surprised when +going down this path :-( ; and (2) being careful about buffering so +that when the tables change you make sure the scanner starts in the +correct state and reading at the right point in the input file. + +> I was wondering if you know of anyone who has used flex in this way. + +I don't - but it seems like a reasonable project to undertake (unlike +numerous other flex tweaks :-). + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-81 +@unnumberedsec unnamed-faq-81 +@example +@verbatim +Received: from 131.173.17.11 (131.173.17.11 [131.173.17.11]) + by ee.lbl.gov (8.9.1/8.9.1) with ESMTP id AAA03838 + for <vern@ee.lbl.gov>; Thu, 20 Aug 1998 00:47:57 -0700 (PDT) +Received: from hal.cl-ki.uni-osnabrueck.de (hal.cl-ki.Uni-Osnabrueck.DE [131.173.141.2]) + by deimos.rz.uni-osnabrueck.de (8.8.7/8.8.8) with ESMTP id JAA34694 + for <vern@ee.lbl.gov>; Thu, 20 Aug 1998 09:47:55 +0200 +Received: (from georg@localhost) by hal.cl-ki.uni-osnabrueck.de (8.6.12/8.6.12) id JAA34834 for vern@ee.lbl.gov; Thu, 20 Aug 1998 09:47:54 +0200 +From: Georg Rehm <georg@hal.cl-ki.uni-osnabrueck.de> +Message-Id: <199808200747.JAA34834@hal.cl-ki.uni-osnabrueck.de> +Subject: "flex scanner push-back overflow" +To: vern@ee.lbl.gov +Date: Thu, 20 Aug 1998 09:47:54 +0200 (MEST) +Reply-To: Georg.Rehm@CL-KI.Uni-Osnabrueck.DE +X-NoJunk: Do NOT send commercial mail, spam or ads to this address! +X-URL: http://www.cl-ki.uni-osnabrueck.de/~georg/ +X-Mailer: ELM [version 2.4ME+ PL28 (25)] +MIME-Version: 1.0 +Content-Type: text/plain; charset=US-ASCII +Content-Transfer-Encoding: 7bit + +Hi Vern, + +Yesterday, I encountered a strange problem: I use the macro processor m4 +to include some lengthy lists into a .l file. Following is a flex macro +definition that causes some serious pain in my neck: + +AUTHOR ("A. Boucard / L. Boucard"|"A. Dastarac / M. Levent"|"A.Boucaud / L.Boucaud"|"Abderrahim Lamchichi"|"Achmat Dangor"|"Adeline Toullier"|"Adewale Maja-Pearce"|"Ahmed Ziri"|"Akram Ellyas"|"Alain Bihr"|"Alain Gresh"|"Alain Guillemoles"|"Alain Joxe"|"Alain Morice"|"Alain Renon"|"Alain Zecchini"|"Albert Memmi"|"Alberto Manguel"|"Alex De Waal"|"Alfonso Artico"| [...]) + +The complete list contains about 10kB. When I try to "flex" this file +(on a Solaris 2.6 machine, using a modified flex 2.5.4 (I only increased +some of the predefined values in flexdefs.h) I get the error: + +myflex/flex -8 sentag.tmp.l +flex scanner push-back overflow + +When I remove the slashes in the macro definition everything works fine. +As I understand it, the double quotes escape the slash-character so it +really means "/" and not "trailing context". Furthermore, I tried to +escape the slashes with backslashes, but with no use, the same error message +appeared when flexing the code. + +Do you have an idea what's going on here? + +Greetings from Germany, + Georg +-- +Georg Rehm georg@cl-ki.uni-osnabrueck.de +Institute for Semantic Information Processing, University of Osnabrueck, FRG +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-82 +@unnumberedsec unnamed-faq-82 +@example +@verbatim +To: Georg.Rehm@CL-KI.Uni-Osnabrueck.DE +Subject: Re: "flex scanner push-back overflow" +In-reply-to: Your message of Thu, 20 Aug 1998 09:47:54 PDT. +Date: Thu, 20 Aug 1998 07:05:35 PDT +From: Vern Paxson <vern> + +> myflex/flex -8 sentag.tmp.l +> flex scanner push-back overflow + +Flex itself uses a flex scanner. That scanner is running out of buffer +space when it tries to unput() the humongous macro you've defined. When +you remove the '/'s, you make it small enough so that it fits in the buffer; +removing spaces would do the same thing. + +The fix is to either rethink how come you're using such a big macro and +perhaps there's another/better way to do it; or to rebuild flex's own +scan.c with a larger value for + + #define YY_BUF_SIZE 16384 + +- Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-83 +@unnumberedsec unnamed-faq-83 +@example +@verbatim +To: Jan Kort <jan@research.techforce.nl> +Subject: Re: Flex +In-reply-to: Your message of Fri, 04 Sep 1998 12:18:43 +0200. +Date: Sat, 05 Sep 1998 00:59:49 PDT +From: Vern Paxson <vern> + +> %% +> +> "TEST1\n" { fprintf(stderr, "TEST1\n"); yyless(5); } +> ^\n { fprintf(stderr, "empty line\n"); } +> . { } +> \n { fprintf(stderr, "new line\n"); } +> +> %% +> -- input --------------------------------------- +> TEST1 +> -- output -------------------------------------- +> TEST1 +> empty line +> ------------------------------------------------ + +IMHO, it's not clear whether or not this is in fact a bug. It depends +on whether you view yyless() as backing up in the input stream, or as +pushing new characters onto the beginning of the input stream. Flex +interprets it as the latter (for implementation convenience, I'll admit), +and so considers the newline as in fact matching at the beginning of a +line, as after all the last token scanned an entire line and so the +scanner is now at the beginning of a new line. + +I agree that this is counter-intuitive for yyless(), given its +functional description (it's less so for unput(), depending on whether +you're unput()'ing new text or scanned text). But I don't plan to +change it any time soon, as it's a pain to do so. Consequently, +you do indeed need to use yy_set_bol() and YY_AT_BOL() to tweak +your scanner into the behavior you desire. + +Sorry for the less-than-completely-satisfactory answer. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-84 +@unnumberedsec unnamed-faq-84 +@example +@verbatim +To: Patrick Krusenotto <krusenot@mac-info-link.de> +Subject: Re: Problems with restarting flex-2.5.2-generated scanner +In-reply-to: Your message of Thu, 24 Sep 1998 10:14:07 PDT. +Date: Thu, 24 Sep 1998 23:28:43 PDT +From: Vern Paxson <vern> + +> I am using flex-2.5.2 and bison 1.25 for Solaris and I am desperately +> trying to make my scanner restart with a new file after my parser stops +> with a parse error. When my compiler restarts, the parser always +> receives the token after the token (in the old file!) that caused the +> parser error. + +I suspect the problem is that your parser has read ahead in order +to attempt to resolve an ambiguity, and when it's restarted it picks +up with that token rather than reading a fresh one. If you're using +yacc, then the special "error" production can sometimes be used to +consume tokens in an attempt to get the parser into a consistent state. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-85 +@unnumberedsec unnamed-faq-85 +@example +@verbatim +To: Henric Jungheim <junghelh@pe-nelson.com> +Subject: Re: flex 2.5.4a +In-reply-to: Your message of Tue, 27 Oct 1998 16:41:42 PST. +Date: Tue, 27 Oct 1998 16:50:14 PST +From: Vern Paxson <vern> + +> This brings up a feature request: How about a command line +> option to specify the filename when reading from stdin? That way one +> doesn't need to create a temporary file in order to get the "#line" +> directives to make sense. + +Use -o combined with -t (per the man page description of -o). + +> P.S., Is there any simple way to use non-blocking IO to parse multiple +> streams? + +Simple, no. + +One approach might be to return a magic character on EWOULDBLOCK and +have a rule + + .*<magic-character> // put back .*, eat magic character + +This is off the top of my head, not sure it'll work. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-86 +@unnumberedsec unnamed-faq-86 +@example +@verbatim +To: "Repko, Billy D" <billy.d.repko@intel.com> +Subject: Re: Compiling scanners +In-reply-to: Your message of Wed, 13 Jan 1999 10:52:47 PST. +Date: Thu, 14 Jan 1999 00:25:30 PST +From: Vern Paxson <vern> + +> It appears that maybe it cannot find the lfl library. + +The Makefile in the distribution builds it, so you should have it. +It's exceedingly trivial, just a main() that calls yylex() and +a yyrap() that always returns 1. + +> %% +> \n ++num_lines; ++num_chars; +> . ++num_chars; + +You can't indent your rules like this - that's where the errors are coming +from. Flex copies indented text to the output file, it's how you do things +like + + int num_lines_seen = 0; + +to declare local variables. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-87 +@unnumberedsec unnamed-faq-87 +@example +@verbatim +To: Erick Branderhorst <Erick.Branderhorst@asml.nl> +Subject: Re: flex input buffer +In-reply-to: Your message of Tue, 09 Feb 1999 13:53:46 PST. +Date: Tue, 09 Feb 1999 21:03:37 PST +From: Vern Paxson <vern> + +> In the flex.skl file the size of the default input buffers is set. Can you +> explain why this size is set and why it is such a high number. + +It's large to optimize performance when scanning large files. You can +safely make it a lot lower if needed. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-88 +@unnumberedsec unnamed-faq-88 +@example +@verbatim +To: "Guido Minnen" <guidomi@cogs.susx.ac.uk> +Subject: Re: Flex error message +In-reply-to: Your message of Wed, 24 Feb 1999 15:31:46 PST. +Date: Thu, 25 Feb 1999 00:11:31 PST +From: Vern Paxson <vern> + +> I'm extending a larger scanner written in Flex and I keep running into +> problems. More specifically, I get the error message: +> "flex: input rules are too complicated (>= 32000 NFA states)" + +Increase the definitions in flexdef.h for: + + #define JAMSTATE -32766 /* marks a reference to the state that always j +ams */ + #define MAXIMUM_MNS 31999 + #define BAD_SUBSCRIPT -32767 + +recompile everything, and it should all work. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-89 +@unnumberedsec unnamed-faq-89 +@example +@verbatim +To: John Victor J <vjohn@its.soft.net> +Subject: Re: flex---is thread safe +In-reply-to: Your message of Sun, 23 May 1999 12:56:56 +0530. +Date: Sun, 23 May 1999 00:32:53 PDT +From: Vern Paxson <vern> + +> I would like to know whether flex is thread safe??? + +I take it you mean the scanners it generates and not flex itself. + +The answer is (still) No, except if you use the -+ option to generate +a C++ scanning class (and if your stream library is thread-safe). + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-90 +@unnumberedsec unnamed-faq-90 +@example +@verbatim +To: "Dmitriy Goldobin" <gold@ems.chel.su> +Subject: Re: FLEX trouble +In-reply-to: Your message of Mon, 31 May 1999 18:44:49 PDT. +Date: Tue, 01 Jun 1999 00:15:07 PDT +From: Vern Paxson <vern> + +> I have a trouble with FLEX. Why rule "/*".*"*/" work properly,=20 +> but rule "/*"(.|\n)*"*/" don't work ? + +The second of these will have to scan the entire input stream (because +"(.|\n)*" matches an arbitrary amount of any text) in order to see if +it ends with "*/", terminating the comment. That potentially will overflow +the input buffer. + +> More complex rule "/*"([^*]|(\*/[^/]))*"*/ give an error +> 'unrecognized rule'. + +You can't use the '/' operator inside parentheses. It's not clear +what "(a/b)*" actually means. + +> I now use workaround with state <comment>, but single-rule is +> better, i think. + +Single-rule is nice but will always have the problem of either setting +restrictions on comments (like not allowing multi-line comments) and/or +running the risk of consuming the entire input stream, as noted above. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-91 +@unnumberedsec unnamed-faq-91 +@example +@verbatim +Received: from mc-qout4.whowhere.com (mc-qout4.whowhere.com [209.185.123.18]) + by ee.lbl.gov (8.9.3/8.9.3) with SMTP id IAA05100 + for <vern@ee.lbl.gov>; Tue, 15 Jun 1999 08:56:06 -0700 (PDT) +Received: from Unknown/Local ([?.?.?.?]) by my-deja.com; Tue Jun 15 08:55:43 1999 +To: vern@ee.lbl.gov +Date: Tue, 15 Jun 1999 08:55:43 -0700 +From: "Aki Niimura" <neko@my-deja.com> +Message-ID: <KNONDOHDOBGAEAAA@my-deja.com> +Mime-Version: 1.0 +Cc: +X-Sent-Mail: on +Reply-To: +X-Mailer: MailCity Service +Subject: A question on flex C++ scanner +X-Sender-Ip: 12.72.207.61 +Organization: My Deja Email (http://www.my-deja.com:80) +Content-Type: text/plain; charset=us-ascii +Content-Transfer-Encoding: 7bit + +Dear Dr. Paxon, + +I have been using flex for years. +It works very well on many projects. +Most case, I used it to generate a scanner on C language. +However, one project I needed to generate a scanner +on C++ lanuage. Thanks to your enhancement, flex did +the job. + +Currently, I'm working on enhancing my previous project. +I need to deal with multiple input streams (recursive +inclusion) in this scanner (C++). +I did similar thing for another scanner (C) as you +explained in your documentation. + +The generated scanner (C++) has necessary methods: +- switch_to_buffer(struct yy_buffer_state *b) +- yy_create_buffer(istream *is, int sz) +- yy_delete_buffer(struct yy_buffer_state *b) + +However, I couldn't figure out how to access current +buffer (yy_current_buffer). + +yy_current_buffer is a protected member of yyFlexLexer. +I can't access it directly. +Then, I thought yy_create_buffer() with is = 0 might +return current stream buffer. But it seems not as far +as I checked the source. (flex 2.5.4) + +I went through the Web in addition to Flex documentation. +However, it hasn't been successful, so far. + +It is not my intention to bother you, but, can you +comment about how to obtain the current stream buffer? + +Your response would be highly appreciated. + +Best regards, +Aki Niimura + + + +--== Sent via Deja.com http://www.deja.com/ ==-- +Share what you know. Learn what you don't. +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-92 +@unnumberedsec unnamed-faq-92 +@example +@verbatim +To: neko@my-deja.com +Subject: Re: A question on flex C++ scanner +In-reply-to: Your message of Tue, 15 Jun 1999 08:55:43 PDT. +Date: Tue, 15 Jun 1999 09:04:24 PDT +From: Vern Paxson <vern> + +> However, I couldn't figure out how to access current +> buffer (yy_current_buffer). + +Derive your own subclass from yyFlexLexer. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-93 +@unnumberedsec unnamed-faq-93 +@example +@verbatim +To: "Stones, Darren" <Darren.Stones@nectech.co.uk> +Subject: Re: You're the man to see? +In-reply-to: Your message of Wed, 23 Jun 1999 11:10:29 PDT. +Date: Wed, 23 Jun 1999 09:01:40 PDT +From: Vern Paxson <vern> + +> I hope you can help me. I am using Flex and Bison to produce an interpreted +> language. However all goes well until I try to implement an IF statement or +> a WHILE. I cannot get this to work as the parser parses all the conditions +> eg. the TRUE and FALSE conditons to check for a rule match. So I cannot +> make a decision!! + +You need to use the parser to build a parse tree (= abstract syntax trwee), +and when that's all done you recursively evaluate the tree, binding variables +to values at that time. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-94 +@unnumberedsec unnamed-faq-94 +@example +@verbatim +To: Petr Danecek <petr@ics.cas.cz> +Subject: Re: flex - question +In-reply-to: Your message of Mon, 28 Jun 1999 19:21:41 PDT. +Date: Fri, 02 Jul 1999 16:52:13 PDT +From: Vern Paxson <vern> + +> file, it takes an enormous amount of time. It is funny, because the +> source code has only 12 rules!!! I think it looks like an exponencial +> growth. + +Right, that's the problem - some patterns (those with a lot of +ambiguity, where yours has because at any given time the scanner can +be in the middle of all sorts of combinations of the different +rules) blow up exponentially. + +For your rules, there is an easy fix. Change the ".*" that comes fater +the directory name to "[^ ]*". With that in place, the rules are no +longer nearly so ambiguous, because then once one of the directories +has been matched, no other can be matched (since they all require a +leading blank). + +If that's not an acceptable solution, then you can enter a start state +to pick up the .*\n after each directory is matched. + +Also note that for speed, you'll want to add a ".*" rule at the end, +otherwise rules that don't match any of the patterns will be matched +very slowly, a character at a time. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-95 +@unnumberedsec unnamed-faq-95 +@example +@verbatim +To: Tielman Koekemoer <tielman@spi.co.za> +Subject: Re: Please help. +In-reply-to: Your message of Thu, 08 Jul 1999 13:20:37 PDT. +Date: Thu, 08 Jul 1999 08:20:39 PDT +From: Vern Paxson <vern> + +> I was hoping you could help me with my problem. +> +> I tried compiling (gnu)flex on a Solaris 2.4 machine +> but when I ran make (after configure) I got an error. +> +> -------------------------------------------------------------- +> gcc -c -I. -I. -g -O parse.c +> ./flex -t -p ./scan.l >scan.c +> sh: ./flex: not found +> *** Error code 1 +> make: Fatal error: Command failed for target `scan.c' +> ------------------------------------------------------------- +> +> What's strange to me is that I'm only +> trying to install flex now. I then edited the Makefile to +> and changed where it says "FLEX = flex" to "FLEX = lex" +> ( lex: the native Solaris one ) but then it complains about +> the "-p" option. Is there any way I can compile flex without +> using flex or lex? +> +> Thanks so much for your time. + +You managed to step on the bootstrap sequence, which first copies +initscan.c to scan.c in order to build flex. Try fetching a fresh +distribution from ftp.ee.lbl.gov. (Or you can first try removing +".bootstrap" and doing a make again.) + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-96 +@unnumberedsec unnamed-faq-96 +@example +@verbatim +To: Tielman Koekemoer <tielman@spi.co.za> +Subject: Re: Please help. +In-reply-to: Your message of Fri, 09 Jul 1999 09:16:14 PDT. +Date: Fri, 09 Jul 1999 00:27:20 PDT +From: Vern Paxson <vern> + +> First I removed .bootstrap (and ran make) - no luck. I downloaded the +> software but I still have the same problem. Is there anything else I +> could try. + +Try: + + cp initscan.c scan.c + touch scan.c + make scan.o + +If this last tries to first build scan.c from scan.l using ./flex, then +your "make" is broken, in which case compile scan.c to scan.o by hand. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-97 +@unnumberedsec unnamed-faq-97 +@example +@verbatim +To: Sumanth Kamenani <skamenan@crl.nmsu.edu> +Subject: Re: Error +In-reply-to: Your message of Mon, 19 Jul 1999 23:08:41 PDT. +Date: Tue, 20 Jul 1999 00:18:26 PDT +From: Vern Paxson <vern> + +> I am getting a compilation error. The error is given as "unknown symbol- yylex". + +The parser relies on calling yylex(), but you're instead using the C++ scanning +class, so you need to supply a yylex() "glue" function that calls an instance +scanner of the scanner (e.g., "scanner->yylex()"). + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-98 +@unnumberedsec unnamed-faq-98 +@example +@verbatim +To: daniel@synchrods.synchrods.COM (Daniel Senderowicz) +Subject: Re: lex +In-reply-to: Your message of Mon, 22 Nov 1999 11:19:04 PST. +Date: Tue, 23 Nov 1999 15:54:30 PST +From: Vern Paxson <vern> + +Well, your problem is the + + switch (yybgin-yysvec-1) { /* witchcraft */ + +at the beginning of lex rules. "witchcraft" == "non-portable". It's +assuming knowledge of the AT&T lex's internal variables. + +For flex, you can probably do the equivalent using a switch on YYSTATE. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-99 +@unnumberedsec unnamed-faq-99 +@example +@verbatim +To: archow@hss.hns.com +Subject: Re: Regarding distribution of flex and yacc based grammars +In-reply-to: Your message of Sun, 19 Dec 1999 17:50:24 +0530. +Date: Wed, 22 Dec 1999 01:56:24 PST +From: Vern Paxson <vern> + +> When we provide the customer with an object code distribution, is it +> necessary for us to provide source +> for the generated C files from flex and bison since they are generated by +> flex and bison ? + +For flex, no. I don't know what the current state of this is for bison. + +> Also, is there any requrirement for us to neccessarily provide source for +> the grammar files which are fed into flex and bison ? + +Again, for flex, no. + +See the file "COPYING" in the flex distribution for the legalese. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-100 +@unnumberedsec unnamed-faq-100 +@example +@verbatim +To: Martin Gallwey <gallweym@hyperion.moe.ul.ie> +Subject: Re: Flex, and self referencing rules +In-reply-to: Your message of Sun, 20 Feb 2000 01:01:21 PST. +Date: Sat, 19 Feb 2000 18:33:16 PST +From: Vern Paxson <vern> + +> However, I do not use unput anywhere. I do use self-referencing +> rules like this: +> +> UnaryExpr ({UnionExpr})|("-"{UnaryExpr}) + +You can't do this - flex is *not* a parser like yacc (which does indeed +allow recursion), it is a scanner that's confined to regular expressions. + + Vern +@end verbatim +@end example + +@c TODO: Evaluate this faq. +@node unnamed-faq-101 +@unnumberedsec unnamed-faq-101 +@example +@verbatim +To: slg3@lehigh.edu (SAMUEL L. GULDEN) +Subject: Re: Flex problem +In-reply-to: Your message of Thu, 02 Mar 2000 12:29:04 PST. +Date: Thu, 02 Mar 2000 23:00:46 PST +From: Vern Paxson <vern> + +If this is exactly your program: + +> digit [0-9] +> digits {digit}+ +> whitespace [ \t\n]+ +> +> %% +> "[" { printf("open_brac\n");} +> "]" { printf("close_brac\n");} +> "+" { printf("addop\n");} +> "*" { printf("multop\n");} +> {digits} { printf("NUMBER = %s\n", yytext);} +> whitespace ; + +then the problem is that the last rule needs to be "{whitespace}" ! + + Vern +@end verbatim +@end example + |