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

sohcahtoa82 at gmail.com sohcahtoa82 at gmail.com
Fri Apr 3 00:26:01 CEST 2015


On Thursday, April 2, 2015 at 2:33:17 PM UTC-7, Thomas 'PointedEars' Lahn wrote:
> Ian Kelly wrote:
> 
> > […] Thomas 'PointedEars' Lahn […] wrote:
> >> Ian Kelly wrote:
> >>> Within a grammar, the question of "is an X a Y" is nonsensical in
> >>> isolation. It can only be answered in relation to a parse tree.
> >>> Consider the simple grammar:
> >>>
> >>> S -> A | B
> >>> A -> x
> >>> B -> x
> >>>
> >>> Is x an A? It depends.
> >>
> >> No, by the definition 2 below, that we all accepted implicitly up to this
> >> point, x is *definitely* an A.
> > 
> > What gives you the impression that I ever accepted it?
> 
> ,-<news:mailman.181.1427346636.10327.python-list at python.org>
> | 
> | What the grammar that you quoted from shows is that STRING+ is an
> | expression.
> 
> There is *no way* for you to make that statement if you did not accept 
> definition (2).
> 
> >> (2) Let the statement “x is an A” be true if x can be produced in a
> >>     production chain starting with or including the non-terminal A
> >>     left-hand side –
> >>
> >>       x ∈ A ↔ ∃A (… ⇒ A ⇒ … ⇒ x).
> > 
> > Sorry, but this definition just seems entirely arbitrary to me.
> 
> It is just the formalization of the definition that we all have agreed to, 
> including you.
> 
> > Mathematically, it looks nonsensical; A is a symbol, not a set.
> 
> “A” is the goal symbol of a production, so it can be interpreted as the 
> superset of all set of terminals that can be produced from it, through the 
> goal symbols that can be produced from it.  And all of us implicitly did 
> that when we said “STRING(+) (literals) is/are (not) (an) expression(s)”.
> 
> > This question of whether "x is an A" is informal and not a topic of formal
> > language theory so far as I'm aware. Can you cite some source for it?
> 
> No, because I was formalizing the ad-hoc definition by Chris Angelico in 
> <news:mailman.51.1426995416.10327.python-list at python.org>.
> 
> >> Now, according to these definitions, in the offered grammar x is *both*
> >> an A and a B.  Because what matters is _not_ the practical result of
> >> production chains (the actual parse tree), but the certainty of the
> >> theoretical possibility of it.
> > 
> > This strikes me as being a lot like arguing, "some kites are toys, and
> > some kites are birds; therefore, all kites are both toys and birds."
> 
> False analogy again.  We are discussing *in theory* a *formal* grammar.  Its 
> goal symbols have *no meaning* except what can be produced from them.
> 
> > As noted above, the inaccuracy that Gregory pointed out has no bearing
> > on my argument.
> 
> But it does.
> 
> > You're really going to make me spell it out, aren't you? Fine, here you
> > go.
> > 
> > single_input -> […] -> expr -> […] -> atom -> STRING STRING
> > 
> > Note: the derivation contains exactly one expr node, which indirectly
> > produces both STRINGs. Neither STRING in this derivation is
> > individually produced from the expr.
> 
> So you have proven that which nobody ever doubted nor requested, but I 
> pointed out already.  What you have still not proven is what you claimed: 
> the parse tree.
> 
> I am sorry that you cannot see that your argument is strewn with gaping 
> defects in logic, but I think I will stop trying to convince you of that 
> now.
> 
> -- 
> PointedEars
> 
> Twitter: @PointedEars2
> Please do not cc me. / Bitte keine Kopien per E-Mail.

*sigh*

https://xkcd.com/386/



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