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From: Panicz Maciej Godek <>
To: Per Bothner <>
Subject: Re: Kawa evaluation process
Date: Tue, 28 Jun 2022 08:17:09 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Thanks for the quick response!

wt., 28 cze 2022 o 07:20 Per Bothner <> napisał(a):

> 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 sounds great!
Actually, I already have a subclass of Pair (because Kawa pairs failed to
work with Java's weak hash tables, because of their identity function):

so what I think I can do is override the getCar and getCdr methods, so that
- if the item held by them is an atom - they would return that atom's
value. (I think it makes sense)

> 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.
That's good to know.
I actually haven't been using PairWithPosition (or subclassing, for that
Instead, I've been using weak-key hash tables representing spaces before
head, after head,
before (dotted) tail and after tail, and some other properties:

I guess that subclassing would result in more efficient code (but I don't
know if I'd be able to change it quickly at this point)

I also wrote my own parser that uses this representation

but I wonder if I could somehow piggyback on your parser to parse atoms?
(I mean something like (call-with-input-string <input> read), but perhaps a
bit more low-level,
because at that point we already know that the thing we're reading isn't a

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/ line 503.
> --
>         --Per Bothner

      reply	other threads:[~2022-06-28  6:17 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-28  4:54 Panicz Maciej Godek
2022-06-28  5:19 ` Per Bothner
2022-06-28  6:17   ` Panicz Maciej Godek [this message]

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