On 24 Jul 2015, at 14:33, Alejandro Zamora Fonseca <terefv@ltu.sld.cu mailto:terefv@ltu.sld.cu> wrote:

Hi!

Just now playing a little with ABCL(1.3.2), I saw some strange behaviour:

CL-USER> '(2 . 5) (2 . 5) CL-USER> '(2 . 5 . 5) (2 . 5) CL-USER> (equal '(2 . 5) '(2 . 5 . 5)) T

while other implementations give me an error when i type '(2 . 5 . 5) it's a bug or ANSI CL allows this?

Depends.

ANSI CL specifies the lisp reader in such a way that (2 . 5 . 5) is not a valid syntax. However, ANSI CL specifies that implementation may extend the CL language, UNDER THE CONDITION that extensions BE DOCUMENTED.

Therefore, IF it is written in ABCL documentation that (2 . 5 . x) reads as (2 . 5) THEN it is not a bug, but an ABCL specific extension, ELSE it is a conformity bug, it should signal a READER-ERROR (or perhaps just an ERROR).

Notice that since this is an extensions on the reader macro character #(, it could be expected that the standard reader macro character for #( still exist in the system and be obtained by (copy-readtable NIL) which shall return the standard readtable. For example, in ccl the default *readtable* is poluted by a lot of extensions such as the dispatching #/ #_ #$ macro characters, but you can throw them away with (setf *readtable* (copy-readtable NIL)). One could expect the same here.

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