destructuring-bind for subset of plist

destructuring-bind for subset of plist

[Sam Halliday]

Hi all,

This causes an error

  (cl-destructuring-bind
      (&key a b)
      '(:a "foo" :b 13 :c "bar")
    (list a b))

because the :c key/value is not handled in the pattern match.

Often I find myself wanting to extract some subset of keys/values from a plist, but cl-destructuring-bind isn't appropriate because of this limitation.

Is there a way to make cl-destructuring-bind simply ignore unmatched keys in the EXPR? I'm not sure what the official common lisp behaviour is supposed to be here, is the error in the spec?

Note that the dash library has some support for a similar destructuring with -let, but that requires some boilerplate to assign a symbol to each key.

Best regards,
Sam

Re: destructuring-bind for subset of plist

[Barry Margolin]

In article <06aeb16e-843c-4964-bf31-09fe16e4488d@googlegroups.com>,
 Sam Halliday <sam.halliday@gmail.com> wrote:

> Hi all,
> 
> This causes an error
> 
>   (cl-destructuring-bind
>       (&key a b)
>       '(:a "foo" :b 13 :c "bar")
>     (list a b))
> 
> because the :c key/value is not handled in the pattern match.
> 
> Often I find myself wanting to extract some subset of keys/values from a 
> plist, but cl-destructuring-bind isn't appropriate because of this 
> limitation.
> 
> Is there a way to make cl-destructuring-bind simply ignore unmatched keys in 
> the EXPR? I'm not sure what the official common lisp behaviour is supposed to 
> be here, is the error in the spec?
> 
> Note that the dash library has some support for a similar destructuring with 
> -let, but that requires some boilerplate to assign a symbol to each key.
> 
> Best regards,
> Sam

In CL you'd use (&key a b &allow-other-keys)

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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