Re: [Sbcl-devel] Failing ADJOIN in SBCL 1.0.16.11

[Scott L. B. <Sc...@sy...>]

Quoting Brian Mastenbrook <br...@ma...>:

> On Apr 27, 2008, at 2:45 PM, Mikael Lax wrote:
>
>> Hi all,
>>
>> the following code:
>>
>> ((lambda (x y)
>>    (adjoin x y :key #'first :test #'string=))
>>  '("B") '(("A")))
>>
>> gives [an error]
>
> The very first thing it does is to pass the list ("B") to STRING=.

Oh, interesting.  I see in CLHS section 17.2.1 that "The function  
designated by the `:key' argument is never called on O itself" (where  
"O" here refers to the first argument to `adjoin').  For some of the  
other routines to which this applies, such as `member', this could  
make sense; but the consequence is that for `adjoin' (and similarly  
`pushnew'), `:key' is useless, since the resulting list will no longer  
have a consistent type.  Instead you'll have to write

   (adjoin x y :test (lambda (x y) (string= (first x) (first y))))

which you might think would mean the same thing, but doesn't.  A  
little unfortunate.

-- Scott