> (aref #(0 1) "0")

Condition of type: SIMPLE-TYPE-ERROR
In function AREF, the index into the object
 #(0 1).
takes a value 0 out of the range (INTEGER 0 1).

>> (format t "~&~@{~12@A ~S~%~}"
        :version (lisp-implementation-version)
        :vcs-id (ext:lisp-implementation-vcs-id)
        :os (software-type)
        :os-version (software-version)
        :machine-type (machine-type)
        :features *features*)

     VERSION "21.2.1"
      VCS-ID "c646799145538997d84ed6d8755be7e7837eb7ef"
          OS "Linux"
  OS-VERSION "6.0.0-6-amd64"
MACHINE-TYPE "x86_64"
    FEATURES (:WALKER :CDR-1 :CDR-5 :LINUX :FORMATTER :CDR-7 :ECL-WEAK-HASH :LITTLE-ENDIAN :ECL-READ-WRITE-LOCK :LONG-LONG :UINT64-T :UINT32-T :UINT16-T :COMPLEX-FLOAT :LONG-FLOAT :UNICODE ...)

     VERSION "21.2.1"
      VCS-ID "c646799145538997d84ed6d8755be7e7837eb7ef"
          OS "Linux"
  OS-VERSION "5.15.0-2-amd64"
MACHINE-TYPE "x86_64"
    FEATURES (:WALKER :CDR-1 :CDR-5 :LINUX :FORMATTER :CDR-7 :ECL-WEAK-HASH
              :LITTLE-ENDIAN :ECL-READ-WRITE-LOCK :LONG-LONG :UINT64-T
              :UINT32-T :UINT16-T :COMPLEX-FLOAT :LONG-FLOAT :UNICODE :DFFI
              :CLOS-STREAMS :CMU-FORMAT :UNIX :ECL-PDE :DLOPEN :CLOS :THREADS
              :BOEHM-GC :ANSI-CL :COMMON-LISP :FLOATING-POINT-EXCEPTIONS
              :IEEE-FLOATING-POINT :PACKAGE-LOCAL-NICKNAMES :CDR-14
              :PREFIXED-API :FFI :X86_64 :COMMON :ECL)

[1]> (ql:quickload :alexandria)
To load "alexandria":
  Load 1 ASDF system:
    alexandria
; Loading "alexandria"
[package alexandria]..............................
[package alexandria-2].
(:ALEXANDRIA)

[2]> (defpackage #:foo (:use #:cl) (:local-nicknames (#:a #:alexandria)))
#<PACKAGE FOO>

[3]> (in-package #:foo)
#<PACKAGE FOO>

FOO[4]> (find-package :a)
#<PACKAGE ALEXANDRIA>

[2]> (defpackage #:foo            
       (:use #:cl)
       (:local-nicknames (#:a #:alexandria)))

*** - EVAL-WHEN: variable #:A has no value
The following restarts are available:
USE-VALUE      :R1      Input a value to be used instead of #:A.
STORE-VALUE    :R2      Input a new value for #:A.
ABORT          :R3      Abort main loop
Break 1 [3]> 

FOO[6]> (macroexpand-1 '(defpackage #:foo (:use #:cl) (:local-nicknames (#:a #:alexandria))))
(EVAL-WHEN (:COMPILE-TOPLEVEL :LOAD-TOPLEVEL :EXECUTE)
 (SYSTEM::%IN-PACKAGE "FOO" :NICKNAMES 'NIL :USE 'NIL :CASE-SENSITIVE NIL :CASE-INVERTED NIL)
 (USE-PACKAGE '("COMMON-LISP") "FOO")
 (DOLIST (SYSTEM::MAPPING (EXT:PACKAGE-LOCAL-NICKNAMES "FOO"))
  (EXT:REMOVE-PACKAGE-LOCAL-NICKNAME (CAR SYSTEM::MAPPING) "FOO"))
 (EXT:ADD-PACKAGE-LOCAL-NICKNAME #:A #:ALEXANDRIA "FOO") (FIND-PACKAGE "FOO")) ;

ECL (Embeddable Common-Lisp) 21.2.1 (git:c646799145538997d84ed6d8755be7e7837eb7ef)
Copyright (C) 1984 Taiichi Yuasa and Masami Hagiya
Copyright (C) 1993 Giuseppe Attardi
Copyright (C) 2013 Juan J. Garcia-Ripoll
Copyright (C) 2018 Daniel Kochmanski
Copyright (C) 2021 Daniel Kochmanski and Marius Gerbershagen
ECL is free software, and you are welcome to redistribute it
under certain conditions; see file 'Copyright' for details.
Type :h for Help.  
Top level in: #<process TOP-LEVEL 0x55c5648bbf80>.

> (declaim (optimize safety))
((OPTIMIZE SAFETY))

> (compile nil '(lambda () (MULTIPLE-VALUE-CALL (LAMBDA (ONE TWO) (LIST ONE TWO)) (VALUES 1 2 3))))
;;; OPTIMIZE levels: Safety=3, Space=0, Speed=3, Debug=0
;;;
;;; End of Pass 1.
#<compiled-function 0x55c565112ac0>
NIL
NIL

> (funcall *)
(1 2)

Neither the standard nor the MOP specify what happens when an error is
signaled in U-I-F-R-C or U-I-F-D-C and control is transferred outside.
This may result in half-baked instances which, respectively, already
have their structure or class changed, but whose newly added slots are
not yet initialized. There is no good way to "fix" the instances afterwards
since, for all purposes, SBCL considers them to be "updated" even though
their slot values are undefined.

This commit modifies the existing behavior in functions
%OBSOLETE-INSTANCE-TRAP and %CHANGE-CLASS by effectively rolling back
the transaction of updating an instance or changing its class if
U-I-F-{R,D}-C does not exit normally but via a nonlocal exit.

The new behavior is actually useful because the programmer can fix
their U-I-F-{R,D}-C code up and either attempt to access the instance
again (to trigger the update process) or call CHANGE-CLASS on it again.

(defmacro prog1 (first &rest body &aux (sym (gensym)))
  "Syntax: (prog1 first-form {form}*)
Evaluates FIRST-FORM and FORMs in order.  Returns the value of FIRST-FORM."
  (if (null body) `(values ,first)
  `(LET ((,sym ,first))
;    (DECLARE (:READ-ONLY ,sym)) ; Beppe
    ,@body ,sym)))

     VERSION "20.4.24"
      VCS-ID "UNKNOWN"
          OS "Linux"
  OS-VERSION "5.9.0-2-amd64"
MACHINE-TYPE "x86_64"
    FEATURES (:WALKER :CDR-1 :CDR-5 :LINUX :FORMATTER :CDR-7 :ECL-WEAK-HASH
              :LITTLE-ENDIAN :LONG-LONG :UINT64-T :UINT32-T :UINT16-T
              :COMPLEX-FLOAT :LONG-FLOAT :UNICODE :DFFI :CLOS-STREAMS
              :CMU-FORMAT :UNIX :ECL-PDE :DLOPEN :CLOS :THREADS :BOEHM-GC
              :ANSI-CL :COMMON-LISP :FLOATING-POINT-EXCEPTIONS
              :IEEE-FLOATING-POINT :PACKAGE-LOCAL-NICKNAMES :CDR-14
              :PREFIXED-API :FFI :X86_64 :COMMON :ECL)

          ;; no way to avoid EVAL here (excluding non-portable hacks)
          (eval `(defgeneric ,lisp-name (object &rest arguments)))
          (eval `(defmethod ,lisp-name ((object qt-object) &rest arguments)
                   (%qinvoke-method object :qt ,qt-name arguments))))))))