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Re: Srfi-159/166 - monadic formatting for guile

From: Linus Björnstam
Subject: Re: Srfi-159/166 - monadic formatting for guile
Date: Fri, 14 Jun 2019 11:38:04 +0200
User-agent: Cyrus-JMAP/3.1.6-663-gf46ad30-fmstable-20190607v1

Hi Mark!

I am not sure I understand what you mean, but i suspect it is already solved, 
since for simple cases show will use display/write. So unless you try to do 
advanced formatting of circular lists it will do whatever display or write 
does. The same thing goes for custom printers. In fact, anything that isn't a 
regular procedure will be printed just as it does in guile. Due to formatters 
being procedures, it is currently not possible to distinguish between 
formatters and other lambdas, but wrapping a lambda in (written ...) works just 
as (write ...). 

So unless you tell show to do something else, it will default do guile's 
standard way. 

(show #t (exact->inexact 1/7)) is the same as (display (exact->inexact 1/7)), 
however (show #t (with ((precision 2)) ...)) is not.

I don't know what circular structures guile uses internally, but (show...)ing a 
circular list without any formatter is, like numbers, the same as whatever 
guile does. (show #t (circular-list 1 2 3)) displays the same as (display 
(circular-list 1 2 3)).

Did I misunderstand your questions?

  Linus Björnstam

On Wed, 12 Jun 2019, at 00:03, Mark H Weaver wrote:
> Hi Linus,
> Linus Björnstam <address@hidden> writes:
> > I just ported the reference implementation of SRFI-159/166 (166 being
> > the successor of 159) from the reference implementation in chibi
> > scheme. The srfi document is here:
> >
> >
> > SRFI-166 is like (ice-9 format) on steroids, drenched in molasses. It
> > can do a lot more than (ice-9 format), but about 3x slower. I haven't
> > started trying to make it fast just yet, but there are some low
> > hanging fruit (like speeding up simple cases). I will wait with
> > optimization until the srfi is finalized (and also maybe hear with
> > Alex what he has in mind before trying to half-ass it myself).
> >
> > Anyway, the repo is here:
> > . I haven't ported the tests, but playing with it in guile and chibi
> > scheme produces the same result. Tests are up, but I'm travelling
> > without computer the next week, so there is no time.
> I would be in favor of integrating this into Guile at some point,
> although first I would like to make a careful review of the
> implementation to make sure that it integrates well with Guile's related
> mechanisms, e.g. custom record printers, printer options, and print
> states, and that it supports all Guile data types.  In particular, I
> remember finding it difficult to properly implement cycle detection
> while supporting Guile's existing mechanisms.  I'm not sure it can be
> done without modifying Guile's built-in printer.
> I'll also want to take a close look at the numeric formatter, to make
> sure that it achieves the same properties as our built-in printer,
> e.g. that it prints inexacts with the minimal number of digits required
> to ensure that the same number will be read back in (unless specifically
> asked to limit the precision).
> Anyway, thanks very much for sharing this!
>     Regards,
>       Mark

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