GNU bug report logs - #76715
30.1; Issues when pretty printing lists with elements ending with a dot

Previous Next

Full log

View this message in rfc822 format

From: Eli Zaretskii <eliz <at> gnu.org>
To: pkryger <at> gmail.com, Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 76715 <at> debbugs.gnu.org
Subject: bug#76715: 30.1; Issues when pretty printing lists with elements ending with a dot
Date: Tue, 04 Mar 2025 14:36:59 +0200

> From: pkryger <at> gmail.com
> Date: Mon, 03 Mar 2025 16:22:04 +0000
> 
> 
> The defualt pretty printing function `pp-fill' yields different output than the expression to be printed. I managed to simplify the cases to the following:
> 
> (let ((pp-default-function #'pp-fill)
>       (fill-column 8))
>   (pp '(x. y. z.)))
> 
> yields output that is not the same expression as the input:
> 
> (x. y
>     . z.)
> 
> When the `fill-column' is smaller (or there are more elements in input) the yielded value is not a valid s-expression
> 
> (let ((pp-default-function #'pp-fill)
>       (fill-column 5))
>   (pp '(x. y. z.)))
> 
> yields:
> 
> (x
>  . y
>  . z.)
> 
> Trying to `read' it back:
> (read
>  (let ((pp-default-function #'pp-fill)
>        (fill-column 5))
>    (pp '(x. y. z.))))
> 
> Yields the following error:
> 
> Debugger entered--Lisp error: (invalid-read-syntax "expected )")
>   read("(x\n . y\n . z.)\n")
>   (progn (read (let ((pp-default-function #'pp-fill) (fill-column 5)) (pp '(x. y. z.)))))
>   eval((progn (read (let ((pp-default-function #'pp-fill) (fill-column 5)) (pp '(x. y. z.))))) t)
>   elisp--eval-last-sexp(nil)
>   #f(compiled-function () #<bytecode 0x518641632d4e2>)()
>   handler-bind-1(#f(compiled-function () #<bytecode 0x518641632d4e2>) (error) eval-expression--debug)
>   eval-last-sexp(nil)
>   funcall-interactively(eval-last-sexp nil)
>   call-interactively(eval-last-sexp nil nil)
>   command-execute(eval-last-sexp)
> 
> For comparison the `pp-29' yields correct output (it's `fill-column' insensitive, hence omitted in the example):
> 
> (let ((pp-default-function #'pp-29))
>   (pp '(x. y. z.)))
> 
> yields (I guess) exepcted output:
> 
> (x. y. z.)
> 
> For a real life error, please see: https://github.com/purcell/package-lint/issues/285

Stefan, any comments or suggestions?

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.