Related articles |
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[3 earlier articles] |
Re: bison and/or antlr ? cfc@shell01.TheWorld.com (Chris F Clark) (2007-07-02) |
Re: bison and/or antlr ? tom@infoether.com (Tom Copeland) (2007-07-03) |
Re: bison and/or antlr ? gneuner2@comcast.net (George Neuner) (2007-07-04) |
Re: bison and/or antlr ? cfc@shell01.TheWorld.com (Chris F Clark) (2007-07-07) |
Re: bison and/or antlr ? gneuner2@comcast.net (George Neuner) (2007-07-09) |
Re: bison and/or antlr ? cfc@shell01.TheWorld.com (Chris F Clark) (2007-07-13) |
Re: bison and/or antlr ? gneuner2@comcast.net (George Neuner) (2007-07-16) |
From: | George Neuner <gneuner2@comcast.net> |
Newsgroups: | comp.compilers |
Date: | Mon, 16 Jul 2007 21:43:16 -0400 |
Organization: | Compilers Central |
References: | 07-06-071 07-07-008 07-07-013 07-07-031 07-07-036 07-07-052 |
Keywords: | parse, tools |
Posted-Date: | 18 Jul 2007 20:02:38 EDT |
On Fri, 13 Jul 2007 11:20:29 -0400, Chris F Clark
<cfc@shell01.TheWorld.com> wrote:
>George Neuner <gneuner2@comcast.net> writes:
>
>> Just to be sure, you are referring to _semantic_ predicates? ...
>> I do find _syntactic_ predicates to be indispensable, ...
>
>No, I was actually referring to syntactic predicates. I agree that
>they are sometimes indispensable, but they also put little loop-holes
>in your grammar, where something in one context parses one way (means
>one thing) and in a different context parses (means) another.
I actually make use of syntactic predicates to deliberately restrict
reuse of subgrammars where there is a possibility of semantic
confusion.
>problem is (particularly with PEG's, which are syntactic predicates on
>steroids) is that there is no check to verify that you haven't
>introduced some corner case you didn't intend to. I don't think that
>there are any PEG generators that even warn you if some rule is
>unreachable. That scares me.
It would scare me also. But I don't use PEGs and that may be why I
like syntax predicates more than you do - I find them indispensable
for CFG. I have rarely written grammars so complex that I couldn't
analyze them with moderate effort - though a DICOM parser I once wrote
pushed the limits.
>By the way, I do feel the same about the precedence and associativity
>declarations in LR parsing. They are great tools, but not for use
>with abandon. They also drop you off the cliff where your tool can't
>tell you that you have mis-specified what you want. Used with care
>that's okay. However, it is too easy to program carelessly.
Which is why I don't use declarations. Although it's more cumbersome
to code precedence hierarchies into the grammar, it's portable and it
makes the grammar easier (IMO) to analyze.
George
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