I wrote a program for removing comment from C source file for which
i...
1.first constructed a DFA
2.used goto statement to write a program.
now it was very easy to model DFA using goto & i suppose it was also
efficient.
so was the use of goto right here?
thanx
Sumit
PUCSD
Nov 15 '05
17  2314 
In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
Incidentally, the removal of comments from C source cannot,
strictly speaking, be done with just a finite state machine
(aka DFA). Additional state (in principle unbounded) is
needed. (I'll just leave this topic here, without saying
why, in case some comp.lang.c readers would enjoy figuring
that out on their own.)
/\
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* Are you referring to comments like this? *\
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/ an******@exampl e.com (Anonymous 7843) writes: In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
Incidentally, the removal of comments from C source cannot,
strictly speaking, be done with just a finite state machine
(aka DFA). Additional state (in principle unbounded) is
needed. (I'll just leave this topic here, without saying
why, in case some comp.lang.c readers would enjoy figuring
that out on their own.)
/\
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* Are you referring to comments like this? *\
\
\
\
/
Yes. The start of that comment needs unbounded
lookahead to tell that it's a comment rather than,
for example, a '/=' operator.
"Tim Rentsch" <tx*@alumnus.ca ltech.edu> wrote in message
news:kf******** *****@alumnus.c altech.edu... an******@exampl e.com (Anonymous 7843) writes:
In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote: >
> Incidentally, the removal of comments from C source cannot,
> strictly speaking, be done with just a finite state machine
> (aka DFA). Additional state (in principle unbounded) is
> needed. (I'll just leave this topic here, without saying
> why, in case some comp.lang.c readers would enjoy figuring
> that out on their own.)
/\
\
\
\
* Are you referring to comments like this? *\
\
\
\
/
Yes. The start of that comment needs unbounded
lookahead to tell that it's a comment rather than,
for example, a '/=' operator.
Uh, no. A comment is syntactically equivalent to a single
space character, which turns any comment of the form
"//**/=" into "/ =".
P.J. Plauger
Dinkumware, Ltd. http://www.dinkumware.com
"P.J. Plauger" <pj*@dinkumware .com> writes: "Tim Rentsch" <tx*@alumnus.ca ltech.edu> wrote in message
news:kf******** *****@alumnus.c altech.edu...
an******@exampl e.com (Anonymous 7843) writes:
In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
>
> Incidentally, the removal of comments from C source cannot,
> strictly speaking, be done with just a finite state machine
> (aka DFA). Additional state (in principle unbounded) is
> needed. (I'll just leave this topic here, without saying
> why, in case some comp.lang.c readers would enjoy figuring
> that out on their own.)
/\
\
\
\
* Are you referring to comments like this? *\
\
\
\
/
Yes. The start of that comment needs unbounded
lookahead to tell that it's a comment rather than,
for example, a '/=' operator.
Uh, no. A comment is syntactically equivalent to a single
space character, which turns any comment of the form
"//**/=" into "/ =".
Right, however that isn't the case I was talking
about. I meant this one:
/\
\
\
\
\
\
=
which looks like it might be a comment until
the scan gets to the '=' character.
In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
an******@exampl e.com (Anonymous 7843) writes:
In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
Incidentally, the removal of comments from C source cannot,
strictly speaking, be done with just a finite state machine
(aka DFA). Additional state (in principle unbounded) is
needed. (I'll just leave this topic here, without saying
why, in case some comp.lang.c readers would enjoy figuring
that out on their own.)
/\
\
\
\
* Are you referring to comments like this? *\
\
\
\
/
Yes. The start of that comment needs unbounded
lookahead to tell that it's a comment rather than,
for example, a '/=' operator.
Unbounded lookahead is not the same as unbounded state. The repetition
of backslash/newline is two states no matter how long it goes on for
and is well within the abilities of a DFA.
However, catering to backslash/newline for every possible token
is a tedious way to implement a lexer. One might prefer to paste the
backslash/newlines together in an early phase, even before removing
comments. an******@exampl e.com (Anonymous 7843) writes: In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
an******@exampl e.com (Anonymous 7843) writes:
In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
>
> Incidentally, the removal of comments from C source cannot,
> strictly speaking, be done with just a finite state machine
> (aka DFA). Additional state (in principle unbounded) is
> needed. (I'll just leave this topic here, without saying
> why, in case some comp.lang.c readers would enjoy figuring
> that out on their own.)
/\
\
\
\
* Are you referring to comments like this? *\
\
\
\
/
Yes. The start of that comment needs unbounded
lookahead to tell that it's a comment rather than,
for example, a '/=' operator.
Unbounded lookahead is not the same as unbounded state. The repetition
of backslash/newline is two states no matter how long it goes on for
and is well within the abilities of a DFA.
However, catering to backslash/newline for every possible token
is a tedious way to implement a lexer. One might prefer to paste the
backslash/newlines together in an early phase, even before removing
comments.
I think you may have missed the significance of the context here.
We weren't talking about writing a lexer. The requirement is for
a program to remove comments from C source code, and except for
removing comments leaves the original source completely intact
(not counting possibly inserting spaces to preserve the token
boundaries around the removed comments).
In this context it's important to know how many \<NL> pairs have
been skipped over, because they may need to be output if they
don't belong to a comment. Needing that count is what changes
the problem to one that can't be done with a finite state
machine.
In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
I think you may have missed the significance of the context here.
We weren't talking about writing a lexer. The requirement is for
a program to remove comments from C source code, and except for
removing comments leaves the original source completely intact
(not counting possibly inserting spaces to preserve the token
boundaries around the removed comments).
In this context it's important to know how many \<NL> pairs have
been skipped over, because they may need to be output if they
don't belong to a comment. Needing that count is what changes
the problem to one that can't be done with a finite state
machine.
You have piqued my curiousity. I'm going to read about flex some more
and have a go at writing a proper comment-removal thingy. I think the
trailing context feature would be sufficient to decide whether or not
to emit backslash/newline, but I'm going to try it out before digging
myself any deeper into the hole. an******@exampl e.com (Anonymous 7843) writes: In article <kf************ *@alumnus.calte ch.edu>,
Tim Rentsch <tx*@alumnus.ca ltech.edu> wrote:
I think you may have missed the significance of the context here.
We weren't talking about writing a lexer. The requirement is for
a program to remove comments from C source code, and except for
removing comments leaves the original source completely intact
(not counting possibly inserting spaces to preserve the token
boundaries around the removed comments).
In this context it's important to know how many \<NL> pairs have
been skipped over, because they may need to be output if they
don't belong to a comment. Needing that count is what changes
the problem to one that can't be done with a finite state
machine.
You have piqued my curiousity. I'm going to read about flex some more
and have a go at writing a proper comment-removal thingy. I think the
trailing context feature would be sufficient to decide whether or not
to emit backslash/newline, but I'm going to try it out before digging
myself any deeper into the hole.
I expect the trailing context feature is sufficient to resolve
the question. Of course, using the trailing context feature
already (in the general case) makes the program exceed what a
finite state machine can do: the trailing context lookahead has
to remember where to continue scanning after checking the
trailing context, and remembering where to go back to takes (in
the theoretical sense) unbounded memory. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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