Re: Kawa evaluation process

[Per Bothner <per@bothner.com>]

On 6/27/22 21:54, Panicz Maciej Godek via Kawa wrote:
> So I've been wondering if there's an option to create a "box" that would be
> transparent to the process of evaluation (possibly with some tweaks to
> Kawa): that I would have an object that holds a string and a value, and
> when the evaluator asks it for the value, it would provide whatever value
> would result from parsing the string?

Wel, we mostly have that.  Every atom (almost - see below) appears as the
car of a cons cell in a list.  So we can associate extra information with
the Pair.  Since Pair is a class you can inherit from, you can create
subclass of Pair with extra information.  This is how line number information
is handled in Kawa - see the PairWithPosition class.

Note a PairWithPosition can specify a range in a sourcefile, which gives you
the actual source string for the atom.  The comments in the file hint at
generalizing the filename/position pair to use a general gnu.text.SourceMapper.
Or you can you can create new subclasses of PairWithPosition.

There are some limitations to the atom/car-of-Pair identity.  One is
in the case of an impure list (dotted pair) - which isn't valid in source code
anyway except inside quotes.  Another limitation is for atoms that are top-level forms.
Kawa handles that by wrapping such an atom in a fake begin list - see
gnu/kawa/lispexpr/LispReader.java line 503.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/