On 10/22/13 11:04 AM, Mark Janssen wrote:
I love it. Watch this...
[context]
A language specification in BNF is just syntax. It doesn't say anything
about semantics. So how could this be used to produce executable C code
for a program? BNF is used to produce parsers. But a parser isn't
sufficient.
A C program is just syntax also. How does the compiler generate
executable machine code? Extrapolate into a Python front-end to C.
[Dave Angel responds:]
Did you even read the paragraph you quoted above? The BNF specification
does NOT completely describe a language, it only defines its syntax.
[Steven D'Aprano responds:]
Like every other language, C programs are certainly not *just* syntax.
Here is some syntax:
&foo bar^ :=
Now, I don't know where y'all were taught Computer Science, but BNF
specifies not only syntax (which would be the *tokens* of a language),
but also its *grammar*; how syntax relates to linguistic categories
like keywords, and tokens relate to each other.
Mark, you had expressed interest in "an app that will take a language
specification in BNF (complete with keywords and all) and output C code
which is then compiled to an executable". I'm interested in how that
app might work.
Here's a BNF for a (very!) simple language:
<program> ::= <number> <op> <number>
<op> ::= "*!?" | "--+" | "..:"
That means these are three valid programs:
123 *!? 456
2 --+ 2
1001 ..: 4
What will the app output as C code for each of these?
Dave is claiming that BNF only defines the syntax of a language, but
then Stephen goes on to supply some syntax that a BNF specification of
the language would not allow (even though Steven calls it "syntax"
which is what BNF in Dave's claim parses).
So which of you is confused? I ask that in the inclusive (not
exclusive OR) sense.... ;^) <-- face says "both".
Could you please be less snarky? We're trying to communicate here, and
it is not at all clear yet who is confused and who is not. If you are
interested in discussing technical topics, then discuss them.
--Ned.
Mark Janssen
Tacoma, Washington.
--
https://mail.python.org/mailman/listinfo/python-list
