Thanks for your answer.
I already integrated such an extension.
S -> expression
expression -> expr(expression)expression -> int
int -> /\d+/
expr(X) -> binop("+", X, X)expr(X) -> binop("-", X,
X)expr(X) -> binop("*", X, X)expr(X) -> binop("/",
X, X)
binop(Op, X, Y) -> X Op Y
It works pretty well, I pushed the fun as to implement currying and few more
features, like self references, inheritance and so on.... it may save a lot
writing without necessarily extending the underlying algorithm.
> Date: Tue, 23 Sep 2014 10:48:38 -0400
> From: [email protected]
> To: [email protected]
> Subject: Re: [PEG] integer encoding // computational model
>
> On 09/23/14 09:29, Abdelkader Belloundja wrote:
> > 3) Sum ( Succ X ) ( Y ) = Succ ( X + Y )
> >
> > The third rule explicitly states a transformation. Could anyone imagine
> > to carry to same amount of meaning in a context-free grammar rule. And
> > if so, how !?
> >
> > I end up with these alternatives :
> >
> > 1) try to stick to the grammar formalism ( the grammar's grammar if you
> > will ) and find another interpretation for it, that would closely
> > ressemble parsing but being synthetical instead of analytical.
> >
> > 2) Incrementally extend the grammar formalism to introduce things like
> > replacement patterns, and make the algorithm support the enhancements.
>
> I'm not sure if it will be useful to your "encoding computation as PEGs"
> project, but I've thought a couple times about doing something like
> replacement patterns as an extension to the PEG formalism. It would be
> more broadly useful for things like programming language grammars: e.g.
> a comma-separated list of FOOs as:
>
> List<FOO> := FOO ( "," FOO )*
>
> which would save you from writing List_Expr and List_Param and who knows
> how many other rules with the same structure. If you made the parameters
> dynamic you could even write a PEG for indentation-based block
> structures (depending on the other features you support), e.g.:
>
> Space<N> := "\t"{N}
> IfExpr<N> := "if" Expr "\n"
> Space<N+1> Expr
> ( Space<N> "else\n"
> Space<N+1> Expr )?
>
>
>
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