Re: intra table reference

[spir <denis.spir@...>]

Tony Finch <dot@dotat.at> dixit:

> On Mon, 30 Nov 2009, spir wrote:
> >
> > Thank you. I think this may be a solution, a kind of table factory.
> >
> > The use case is to build parsers/grammars as tables of (named) patterns.
> > This seems to me rather an obvious solution in Lua. However,
> > higher-level patterns need to reference lower-level ones, eg integer =
> > OneOrMore(digit).
> 
> I do this when writing LPEG grammars.
> 
> The basic pattern is below. Sometimes I return the whole pattern
> environment, in which case match operations look like
> parser.thing:match(str), or I just return the start symbol so match
> operations are parser:match(str)
> 
> Note this code uses my LPEG patch so % operators are not necessary to
> access the pattern environment, and I've also used a pythonic % operator.
> 
> 	local function make_parser()
> 		-- environment for non-terminals
> 		local env = {}
> 		local function p(pat)
> 			return re.compile(pat, env)
> 		end
> 		setfenv(1,env)
> 
> 		-- define grammar here

                [...]

> 		return env
> 	end
> 	local parser = make_parser()
> 
> Tony.

Thank you, that's exactly the approach I was looking for.

Denis
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