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Re: Correct line/column numbers in byte compiler messages [Was: GNU is l

From: Clément Pit-Claudel
Subject: Re: Correct line/column numbers in byte compiler messages [Was: GNU is looking for Google Summer of Code Projects]
Date: Fri, 20 Mar 2020 17:27:34 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 20/03/2020 16.10, Alan Mackenzie wrote:
> Are you saying that this is how other Lisp compilers deal with
> source code positions?  How do they deal with the difficult problem
> of user macros?  Could you give me an example of a free Lisp system
> which works this way?  I'd be interested in having a look at it.

not sure if it counts as a Lisp compiler, but Racket does this; the "fat cons 
cells" are called syntax objects.  See 
https://blog.racket-lang.org/2011/04/writing-syntax-case-macros.html for a good 
explanation, including this intro:

> The main idea with Racket’s macro system (and with other syntax-case
> systems) is that macros are syntax-to-syntax functions, just like the
> case of defmacro, except that instead of raw S-expressions you’re
> dealing with syntax objects. This becomes very noticeable when
> identifiers are handled: instead of dealing with plain symbols,
> you’re dealing with these syntax values (called “identifiers” in this
> case) that are essentially a symbol and some opaque information that
> represents the lexical scope for its source. In several syntax-case
> systems this is the only difference from defmacro macros, but in the
> Racket case this applies to everything — identifiers, numbers, other
> immediate constants, and even function applications, etc — they are
> all the same S-expression values that you’re used to, except wrapped
> with additional information. Another thing that is unique to Racket
> is the extra information: in addition to the opaque lexical context,
> there is also source information and arbitrary properties (there are
> also certificates, but that’s ignorable for this text).
It would be worth checking more closely what Guile does.  Its 
syntax-manipulating functions automatically propagate "source properties", but 
from reading 
https://www.gnu.org/software/guile/manual/html_node/Source-Properties.html it 
seems that it might use something similar to your approach?


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