Jacob Fugal wrote:
On Mon, Jun 30, 2008 at 9:58 AM, Michael Torrie <[EMAIL PROTECTED]> wrote:
Hans Fugal wrote:
In which way? They take ascii art as input? I had no trouble with the
syntax diagrams in 431, but I found them hard to work with. I couldn't
send one by email easily. I had to have a PDF viewer and scan through
dozens of pages of diagrams (we know how much fun that can be) or lug
the large book (which I printed out at Kinkos) around. I decided to
write my own parser generator, and so I had to enter all those diagrams
into BNF format (which seemed like a reasonable machine-readable
choice), and while tedious I don't remember it being difficult. In fact,
I seem to remember very quickly finding a few patterns, and converting
to BNF was primarily a rote exercise.
Good point. I presume from a casual googling that ANTLR must have some
notation that allows one to easily define a syntax diagram using some
notation. I would guess (and that's all it is) that the syntax would be
similar to how PyParsing defines a grammar. Easy ways to say "one or
more" or "zero or more," for example. Given that format it is just as
clear and easy to run through a parser generator as BNF.
From my understanding, this is one of the major differences between
BNF and EBNF. EBNF allows specifying right repetition ala:
expr -> term { addop term }
addop -> "+" | "-"
and optionality ala:
if-stmt -> "if" expr "then" stmt-block [ "else" stmt-block ]
These constructions covert really easily into both a syntax diagram
and a recursive descent implementation. Maybe I'm misremembering,
though.
Jacob Fugal
Good point, and I was using EBNF not straight BNF (which only has
theoretical value, IMHO).
--
Hans Fugal ; http://hans.fugal.net
There's nothing remarkable about it. All one has to do is hit the
right keys at the right time and the instrument plays itself.
-- Johann Sebastian Bach
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