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Re: A simple single line, triple-quoted comment is giving syntax error. Why?

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From Gregory Ewing <greg.ewing@canterbury.ac.nz>
Newsgroups comp.lang.python
Subject Re: A simple single line, triple-quoted comment is giving syntax error. Why?
Date Fri, 27 Mar 2015 11:43:29 +1300
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Ian Kelly wrote:
> What I mean is that if you construct a parse tree of "foo" "bar" using
> that grammar, it looks like this:
> 
>      expr
>        |
>     STRING+
>      /   \
> STRING  STRING

Not quite -- STRING+ is not a symbol in the grammar, it's
a shorthand for a combination of symbols. The parse tree
is actually just

       expr
       /   \
  STRING  STRING

> Not like this:
> 
>     expr
>      |
>    STRING+
>     /  \
>  expr  expr
>   |      |
> STRING  STRING

That would be

 >     expr
 >     /  \
 >  expr  expr
 >   |      |
 > STRING  STRING

Thomas 'PointedEars' Lahn wrote:
 > Prove it.

To get a parse tree like the above, there would need to be
a production like this in the grammar:

    expr ::= expr+

There is no such production, so that parse tree is impossible.
QED.

What you seem to be doing in your mind is taking this
production:

    expr ::= STRING

and using it "backwards" to justify expanding any occurrence
of STRING into expr. But grammars don't work that way. You're
committing a logical fallacy: just because some exprs are
STRINGs doesn't mean that all STRINGs are exprs.

-- 
Greg

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A simple single line, triple-quoted comment is giving syntax error. Why? Aditya Raj Bhatt <adityarajbhatt@gmail.com> - 2015-03-18 10:46 -0700
  Re: A simple single line, triple-quoted comment is giving syntax error. Why? Laurent Pointal <laurent.pointal@laposte.net> - 2015-03-18 19:04 +0100
    Re: A simple single line, triple-quoted comment is giving syntax error. Why? Laurent Pointal <laurent.pointal@laposte.net> - 2015-03-18 19:06 +0100
      Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-18 20:53 +0100
        Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-18 20:56 +0100
        Re: A simple single line, triple-quoted comment is giving syntax error. Why? Terry Reedy <tjreedy@udel.edu> - 2015-03-18 17:47 -0400
        Re: A simple single line, triple-quoted comment is giving syntax error. Why? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-19 09:58 +1100
          Re: A simple single line, triple-quoted comment is giving syntax error. Why? Chris Angelico <rosuav@gmail.com> - 2015-03-19 10:23 +1100
    Re: A simple single line, triple-quoted comment is giving syntax error. Why? Aditya Raj Bhatt <adityarajbhatt@gmail.com> - 2015-03-18 11:23 -0700
      Re: A simple single line, triple-quoted comment is giving syntax error. Why? Igor Korot <ikorot01@gmail.com> - 2015-03-18 14:45 -0400
      Re: A simple single line, triple-quoted comment is giving syntax error. Why? Laurent Pointal <laurent.pointal@laposte.net> - 2015-03-18 20:08 +0100
      Re: A simple single line, triple-quoted comment is giving syntax error. Why? Tim Roberts <timr@probo.com> - 2015-03-28 16:34 -0700
  Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-18 21:21 +0100
  Re: A simple single line, triple-quoted comment is giving syntax error. Why? Tim Chase <python.list@tim.thechases.com> - 2015-03-18 13:15 -0500
  Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ben Finney <ben+python@benfinney.id.au> - 2015-03-19 11:06 +1100
  Re: A simple single line, triple-quoted comment is giving syntax error. Why? Denis McMahon <denismfmcmahon@gmail.com> - 2015-03-19 00:53 +0000
    Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-22 04:14 +0100
      Re: A simple single line, triple-quoted comment is giving syntax error. Why? Chris Angelico <rosuav@gmail.com> - 2015-03-22 14:36 +1100
        Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-22 04:49 +0100
          Re: A simple single line, triple-quoted comment is giving syntax error. Why? Chris Angelico <rosuav@gmail.com> - 2015-03-22 15:11 +1100
            Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-26 05:35 +0100
              Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-25 23:09 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-26 17:45 +0100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-26 12:29 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-26 19:54 +0100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-26 17:27 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-28 19:20 +0100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-29 01:56 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-29 12:41 +0200
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-31 01:23 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? sohcahtoa82@gmail.com - 2015-03-31 16:10 -0700
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Chris Angelico <rosuav@gmail.com> - 2015-04-01 10:36 +1100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-31 17:43 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-04-02 23:31 +0200
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? sohcahtoa82@gmail.com - 2015-04-02 15:26 -0700
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-02 18:21 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-03 16:40 +1100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Chris Angelico <rosuav@gmail.com> - 2015-04-03 16:57 +1100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Marko Rauhamaa <marko@pacujo.net> - 2015-04-03 10:13 +0300
                r"\"" ??? (was A simple single line, triple-quoted comment) Rustom Mody <rustompmody@gmail.com> - 2015-04-03 05:52 -0700
                Re: r"\"" ??? (was A simple single line, triple-quoted comment) Chris Angelico <rosuav@gmail.com> - 2015-04-04 01:40 +1100
                Re: r"\"" ??? (was A simple single line, triple-quoted comment) Rustom Mody <rustompmody@gmail.com> - 2015-04-03 08:14 -0700
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-03 09:25 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-03 00:40 -0600
                Re: A simple single line, triple-quoted comment is giving syntax   error. Why? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-03-27 11:43 +1300
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-28 19:06 +0100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-26 12:32 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-26 19:56 +0100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-27 10:15 +1100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Tim Chase <python.list@tim.thechases.com> - 2015-03-26 18:47 -0500
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-26 19:38 -0600
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Marko Rauhamaa <marko@pacujo.net> - 2015-03-27 07:34 +0200
              Re: A simple single line, triple-quoted comment is giving syntax error. Why? Dave Angel <davea@davea.name> - 2015-03-26 01:23 -0400
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-26 18:25 +0100
                Re: A simple single line, triple-quoted comment is giving syntax error. Why? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-03-26 18:30 +0100
          Re: A simple single line, triple-quoted comment is giving syntax error. Why? Marko Rauhamaa <marko@pacujo.net> - 2015-03-22 12:00 +0200

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