Sender: lojban@googlegroups.com
Date: Tue, 14 Apr 2020 08:57:50 -0700 (PDT)
From: Gleki Arxokuna <gleki.is.my.name@gmail.com>
To: lojban <lojban@googlegroups.com>
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Subject: [lojban] Re: Where is the latest/official PEG grammar?
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Em ter=C3=A7a-feira, 14 de abril de 2020 18:34:47 UTC+3,=20
scope845hlang343jbo@icebubble.org escreveu:
>
> Gleki Arxokuna <gleki.is.my.name@gmail.com> writes:=20
>
> > PEG has its own deficiencies.=20
>
> What deficiencies?=20
>
> > True. PEG won't put us forward significantly.=20
>
> Why wouldn't it?  Having a complete specification of the language seems=
=20
> like it would be a HUGE step forward, to me.  From PEG, it would be but=
=20
> a short distance to having a working, fully-correct parser.=20
>
> >> Maybe that's what we're waiting for?  A proof that the PEG grammar is=
=20
> >> backward-compatible with the YACC?  =20
> >=20
> >=20
> > Its not backward compatible by definition.=20
>
> It would have to be.  Otherwise, currently (and historically)=20
> grammatical Lojban wouldn't be grammatical under the new (PEG=20
> specification of the) grammar.  Am I wrong?=20
>
> >> IfIf so, the second half of Bryan=20
> >> Ford's thesis paper on PEGs describes how to transform parsing=20
> >> expressions into other forms which could be compared with the YACC.=20
> >=20
> >=20
> > Transformation doesn't necessarily imply equivalence.=20
>
> No, but it would render the PEG in a form which could be *compared* to=20
> the YACC.  If you cut-out the morphology rules,


You need to cut out much more. Compare how many lines the BNF grammar has.=
=20
One can learn it by heart. Now compare to camxes grammars.=20

> and allow for changes=20
> for handling elidable terminators and metalinguistic erasers, the=20
> remainder (the bulk) of the grammar should be formally equivalent to the=
=20
> current YACC grammar.300.  That would prove that the YACC and PEG parse=
=20
> essentially the same language.  Given such a proof, is there any reason=
=20
> why such a PEG would NOT be accepted as the new baseline grammar?=20
>

Because PEG formalism doesn't allow checking for ambiguities. E.g. PEG is=
=20
unambiguous even if you add to it rules and subrules that would never=20
match.=20

But seriously PEG/CFG are not powerful enough even by BPFK standards (see=
=20
BPFK pages in the wiki)

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<div dir=3D"ltr"><br><br>Em ter=C3=A7a-feira, 14 de abril de 2020 18:34:47 =
UTC+3, scope845hlang343jbo@icebubble.org  escreveu:<blockquote class=3D"gma=
il_quote" style=3D"margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid=
;padding-left: 1ex;">Gleki Arxokuna &lt;<a href=3D"mailto:gleki.is.my.name@=
gmail.com" target=3D"_blank" rel=3D"nofollow" onmousedown=3D"this.href=3D&#=
39;mailto:gleki.is.my.name@gmail.com&#39;;return true;" onclick=3D"this.hre=
f=3D&#39;mailto:gleki.is.my.name@gmail.com&#39;;return true;">gleki.is.my.n=
ame@gmail.com</a>&gt; writes:
<br>
<br>&gt; PEG has its own deficiencies.
<br>
<br>What deficiencies?
<br>
<br>&gt; True. PEG won&#39;t put us forward significantly.
<br>
<br>Why wouldn&#39;t it? =C2=A0Having a complete specification of the langu=
age seems
<br>like it would be a HUGE step forward, to me. =C2=A0From PEG, it would b=
e but
<br>a short distance to having a working, fully-correct parser.
<br>
<br>&gt;&gt; Maybe that&#39;s what we&#39;re waiting for? =C2=A0A proof tha=
t the PEG grammar is=20
<br>&gt;&gt; backward-compatible with the YACC? =C2=A0
<br>&gt;
<br>&gt;
<br>&gt; Its not backward compatible by definition.
<br>
<br>It would have to be. =C2=A0Otherwise, currently (and historically)
<br>grammatical Lojban wouldn&#39;t be grammatical under the new (PEG
<br>specification of the) grammar. =C2=A0Am I wrong?
<br>
<br>&gt;&gt; IfIf so, the second half of Bryan=20
<br>&gt;&gt; Ford&#39;s thesis paper on PEGs describes how to transform par=
sing=20
<br>&gt;&gt; expressions into other forms which could be compared with the =
YACC.
<br>&gt;
<br>&gt;
<br>&gt; Transformation doesn&#39;t necessarily imply equivalence.
<br>
<br>No, but it would render the PEG in a form which could be *compared* to
<br>the YACC. =C2=A0If you cut-out the morphology rules,</blockquote><div><=
br></div><div>You need to cut out much more. Compare how many lines the BNF=
 grammar has. One can learn it by heart. Now compare to camxes grammars.=C2=
=A0</div><blockquote class=3D"gmail_quote" style=3D"margin: 0;margin-left: =
0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"> and allow for change=
s
<br>for handling elidable terminators and metalinguistic erasers, the
<br>remainder (the bulk) of the grammar should be formally equivalent to th=
e
<br>current YACC grammar.300. =C2=A0That would prove that the YACC and PEG =
parse
<br>essentially the same language. =C2=A0Given such a proof, is there any r=
eason
<br>why such a PEG would NOT be accepted as the new baseline grammar?
<br></blockquote><div><br></div><div>Because PEG formalism doesn&#39;t allo=
w checking for ambiguities. E.g. PEG is unambiguous even if you add to it r=
ules and subrules that would never match.=C2=A0</div><div><br></div><div>Bu=
t seriously PEG/CFG are not powerful enough even by BPFK standards (see BPF=
K pages in the wiki)</div></div>

<p></p>

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