Destructuring lambda lists are unwarrantedly lax in their treatment of invalid or misplaced lambda list keywords

Bug #708051 reported by Jean-Philippe Paradis on 2011-01-26
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Douglas Katzman

Bug Description

What I do:
(destructuring-bind (&whole &optional test this) '(value)
  (values test this))

(destructuring-bind (a b &keys c) '(va vb)
  a b c)

What happens:
1. &optional is treated just like if it was any other reasonable variable name for &whole.

2. &keys is treated just like if it was any other reasonable variable name for a required argument. (it's obvious the user meant &key. However this pertains to any bogus lambda list keyword, not just small typos)

What I expected to happen:
1. This should be treated as &whole missing its parameter and reported as an error. The behavior should be similar to having &whole or &rest or &body at the end of the list with a missing parameter, but perhaps with a more precise error message such as "Unexpected lambda list keyword &optional found instead of argument to &whole".

2. Symbols beginning with "&" should be treated as "apparent lambda list keywords" and never accepted as variable names. Nobody sane would use such apparent lambda list keywords as variable names. A distinction should be made between actual lambda list keywords (for which (member symbol lambda-list-keywords) => T) and bogus lambda list keywords (for which (member symbol lambda-list-keywords) => NIL) for error detection and error reporting purposes.

SBCL version: 1.0.42
uname -a: Linux dynamorph 2.6.32-27-generic #49-Ubuntu SMP Wed Dec 1 23:52:12 UTC 2010 i686 GNU/Linux


Nikodemus Siivola (nikodemus) wrote :

I agree in the main, but not to all details.

&KEYS is a valid variable name -- but since it is likely to be a typo, a style-warning is definitely in order.

Changed in sbcl:
importance: Undecided → Low
status: New → Triaged
Douglas Katzman (dougk) on 2015-06-11
Changed in sbcl:
assignee: nobody → Douglas Katzman (dougk)
Douglas Katzman (dougk) on 2015-07-02
Changed in sbcl:
status: Triaged → Fix Committed
Changed in sbcl:
status: Fix Committed → Fix Released
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