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

From: Mark H Weaver
Subject: Re: Srfi-159/166 - monadic formatting for guile
Date: Sun, 16 Jun 2019 15:30:07 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Hi John,

John Cowan <address@hidden> writes:

> On Sun, Jun 16, 2019 at 2:47 AM Mark H Weaver <address@hidden> wrote:
>> How do you implement 'written-shared', 'pretty-shared', and
>> 'trimmed/lazy'?  In particular, how do you avoid non-termination when
>> asked to print cyclic data, when the cycle includes a non-standard data
>> type printed using a custom printer?  For example, what if you print a
>> list that includes an object whose custom printer will print output that
>> includes the same list that you started with?
> Of course it can't cope with that.  But consider an object whose custom
> printer outputs its instance variables where one of those instance variables
> has been assigned to the object itself.  No procedure other than the object
> printer itself is going to be able to break *that* loop.

The built-in 'write' and 'display' procedures can break the loop, which
is the approach that I chose when I last looked at this.


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