On Tuesday, March 31, 2015 at 12:24:53 AM UTC-7, Ian wrote: > On Sun, Mar 29, 2015 at 4:41 AM, Thomas 'PointedEars' Lahn > <pointede...@web.de> wrote: > > Ian Kelly wrote: > > > >> […] Thomas 'PointedEars' Lahn […] wrote: > >>> Ian Kelly wrote: > >> Why should the burden of proof be on me in the first place? > > > > Because *you* made the claim that “STRING+” could be part of an AST in this > > way. > > Okay, I didn't understand before that this was the part that you were > objecting to. I had written "There is only one expr node, and it > contains both STRING tokens", to which you replied "Prove it." I did > not intend to imply anything at all by the inclusion of STRING+ in the > tree. That pseudo-tree was hastily sketched out, and as both you and > Gregory have pointed out, STRING+ is not a symbol of the grammar and > should not have been included as a node. None of this has any bearing > on what I was trying to demonstrate with that tree. > > >> 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? > > >> If the tree that generates the x produces it from an A node, then yes. > >> Otherwise, no. > > > > Fallacy. > > > > First, two definitions, so that we are clear what we are talking about: > > > > (1) Let a *production chain* be the repeated application of the production > > rules of a formal grammar such that > > > > C ⇒ D ⇒ x > > > > is a production chain if there are production rules > > > > C → D > > D → x. > > > > [Note the difference between “⇒” and “→”.] > > Sure. > > > (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. > Mathematically, it looks nonsensical; A is a symbol, not a set. 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? > > > 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." > > >> So when I write that the "foo" in "foo" "bar" is not an expression, I > >> am only speaking in relation to the parse tree that generates "foo" > >> "bar". > > > > But it has been indicated by others that the parse tree that you presented > > is wrong, based on a misconception about the syntax of the formal grammar, > > and you have not yet substantiated your claim that it is correct. > > As noted above, the inaccuracy that Gregory pointed out has no bearing > on my argument. > > You're really going to make me spell it out, aren't you? Fine, here you go. > > single_input -> simple_stmt -> expr_stmt -> testlist_star_expr -> test > -> or_test -> and_test -> not_test -> comparison -> expr -> xor_expr > -> and_expr -> shift_expr -> arith_expr -> term -> factor -> power -> > 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. > > >> I don't know what you mean by a "backdoor". > > > > Appending a statement that is contradictory to what was stated just before, > > or at least ambiguous, so that the possibility arises for one to say “I did > > not mean that” when that/a contradiction to the former statement is pointed > > out later. > > The purpose was not to make the possibility arise to say that. The > purpose was to point out the discontinuity *immediately* so that it > would be already addressed and not *need* to be pointed out later > (although we can see how well that turned out). > > I have to say that I find it highly surprising that you find this > construction objectionable. Would you still consider it > "contradictory" if I had phrased it equivalently as a logical "or" > rather than using the word "except"? > > >> The purpose of that parenthetical was to explicitly acknowledge that the > >> single STRING could be viewed as an expression when taken out of context, > > > > Yes, your fallacy is mainly based on ignoring the context. Context is > > important; you cannot just ignore it and still make correct arguments. > > Funny, I thought that was my line. This whole argument came about > because you seem to be stubbornly insistent on ignoring the context > that I set for my statement, calling it "contradictory" instead. > > >> and to disclaim that I was excluding that case from the preceding > >> statement. I still stand by that statement; The "foo" in "foo" "bar" is > >> not an expression in the same sense that the "42" is not an expression in > >> "hucr,.@#%c|42ptqc$". > > > > False analogy. The “42” in there cannot be produced by “expr” *in that > > context* (it can only be produced by “STRING”). > > I apologize for the confusion. The quotation marks there were only > intended to separate the nonsense construction from my own text, not > as string delimiters. I realize that in the first part of the analogy > I did use them as string delimiters, so I was inconsistent. > > The analogy to be drawn is that a parse tree of ⟨"foo" "bar"⟩ that > contains an expr node for each STRING is an invalid parse, just as a > parse tree of ⟨hucr,.@#%c|42ptqc$⟩ that isolates ⟨42⟩ as a single expr > (or any other parse tree in this particular case) is invalid. > > >>> Actually, you were arguing against my statement that string literals are > >>> expressions (that a string literal is an expression). You claimed, > >>> rather explicitly, that they were not. See above. > >> > >> I have no idea what point you're trying to convey here. > > > > Is the “See above” not enough a reference? > > I get the connection between what you wrote here and what you wrote > above. I don't get the connection between what I wrote (that has now > been trimmed away) and what you wrote in response to it. My > parenthetical about parsing STRINGs in isolation was not in itself an > argument against what you wrote. It was in fact agreeing, within a > limited context.
Holy hell, dude, you've been arguing about this for nearly two weeks now. Let it go. -- https://mail.python.org/mailman/listinfo/python-list
