6 Oct
2011
6 Oct
'11
6:45 p.m.
1. in PPMSEGrammar, start is encoded ad ^elements end
is that a good habit to include end in start method? Somehow this is counter
intuitive to me since it seems it would make such grammar non embeddable in
another parser, or I am mistaken?
Yeah, I think this is like a pattern. #start is just the default
production when the parser is used standalone. When you compose it
with some other parser you could directly go with whatever other
production you want, i.e.
PPMSEGrammar new elements
2. can ==> be cascaded in a sense that if we have
parser A, its subclass
parser B which calls supper and then adds ==>. Can we then have C which is
subclass of B, and adds its ==> on top of the one added by B?
It is always cascaded. #==> just wraps the receiver with the action
block, so if you write
p := (#word asParser
==> [ :each | each asUppercase ])
==> [ :each | each asciiValue ].
p parse: 'a' --> returns 65, the ascii code of $A
3. What do you think, could PettitParser be reasonably
used to de-marshal
some (binary) network protocol. By reasonably I mean that it would not be an
order of magnitude slower than some code hacked from the scratch (but not
terribly optimized).
Definitely. You would probably need to implement some special stream
that works on the bit-level. Marcus and I once started to write a
bytecode decompiler, that worked reasonably well but I don't know the
status.
An optimized hand written parser is certainly faster. For performance
I typically compare the hand written parser of the refactoring engine
(RBParser) and the strictly equivalent one in PetitParser
(PPSmalltalkParser). The hand written one is about 3.3 times faster.
Lukas
--
Lukas Renggli
www.lukas-renggli.ch