From: mf <massifr@fastwebnet.it>
To: ntg-context@ntg.nl
Subject: Re: Access current element in xmlsetsetup via xml.expressions
Date: Wed, 2 Oct 2019 12:32:14 +0200 [thread overview]
Message-ID: <6c559d5e-0b91-8b7b-95a9-be3d29736e89@fastwebnet.it> (raw)
In-Reply-To: <2E39AF70-9E74-41DE-B87B-0C3DE20B3585@elvenkind.com>
The answer is in lxml-lpt.lua, where built-in expressions are defined.
You need a good knowledge of LPEG that i miss.
Some built-in expressions get the current element as first argument,
like count() or child() (lines 1300-1307 of lxml-lpt.lua):
expressions.child = function(e,pattern)
return applylpath(e,pattern) -- todo: cache
end
expressions.count = function(e,pattern) -- what if pattern == empty or nil
local collected = applylpath(e,pattern) -- todo: cache
return pattern and (collected and #collected) or 0
end
Some other expressions use a template that passes the "list", "ll", "l"
and "order" arguments you find cited in the XML manual §4.1 "Path
expressions - Expressions and filters".
These are the lines 738-743 in lxml-lpt.lua:
local template_e = [[
local expr = xml.expressions
return function(list,ll,l,order)
return %s
end
]]
That template is used by the function that registers a new expression
(lines 807-812 in lxml-lpt.lua):
local function register_expression(expression)
local converted = lpegmatch(converter,expression)
local runner = load(format(template_e,converted))
runner = (runner and runner()) or function()
errorrunner_e(expression,converted) end
return { kind = "expression", expression = expression, converted =
converted, evaluator = runner }
end
Anyway i could not find a way to define an expression with a function
like this:
xml.expressions.myexpr( ... )
that gets access to those arguments.
The only arguments it gets are the ones you specify in your LPATH
expressions; AFAIK they are attributes values -- with the @attr syntax
-- and strings.
Best wishes,
Massi
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next prev parent reply other threads:[~2019-10-02 10:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-01 19:24 achim
2019-10-02 8:18 ` Taco Hoekwater
2019-10-02 10:32 ` mf [this message]
2019-10-02 16:52 ` Hans Hagen
2019-10-02 17:48 ` achim
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