Ian Kelly wrote:
> […] Thomas 'PointedEars' Lahn […] wrote:
>> Ian Kelly wrote:
>>> What the grammar that you quoted from shows is that STRING+ is an
>>> expression. The individual STRINGs of a STRING+ are not expressions,
>>> except to the extent that they can be parsed in isolation as a
>>> STRING+.
>> How did you get that idea? STRING+ means one or more consecutive STRING
>> tokens (ignoring whitespace in-between), which means one or more
>> consecutive string literals. A (single) string literal definitely is an
>> expression as it can be produced with the “expr” goal symbol of the
>> Python grammar (given there in a flavor of EBNF).
>
> Yes, that's what I was referring to in my parenthetical "except..." above.
Your “except” is contradictory to the rest of what you said, at best.
> 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
> […]
>
> There is only one expr node, and it contains both STRING tokens.
Prove it.
But be warned: Neither would prove that a string literal is not an
expression. Because you did not consider the most simple variant of an AST
(or subtree) according to this grammar:
expr
|
STRING
Again, “STRING+” does _not_ mean “STRING STRING STRING*”; it means “STRING
STRING*”. The second and following STRINGs are *optional*.
>> […] in the used flavour of EBNF the unquoted “+” following a goal symbol
>> clearly means the occurrence of *at least one* of the immediately
>> preceding symbol, meaning either one *or more than one*.
>
> It means one or more *tokens*, not one or more literals.
Utter nonsense. Have you ever written a parser? (I have.) A literal *is*
a token. Whether two consecutive tokens end up as the same *node* in an AST
is a *different* issue (that, again, was _not_ debated).
--
PointedEars
Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.
--
https://mail.python.org/mailman/listinfo/python-list
