On Thu, Jan 01, 2015 at 10:46:44AM +0100, Alexander Burger wrote:
> You can use '@' as a placeholder to ignore parts of a pattern:
>
> (let (((A . @) @ @ D) '((1 2 3) (4 5 6) 7 8 9))
> (trail T) )
> -> (A 1 D 8)
>
> '@' is not bound to the matching values and thus saves stack space.
Please note that I changed '@' to 'NIL' for "don't care" positions.
The above example should now be written as
(let (((A . NIL) NIL NIL D) '((1 2 3) (4 5 6) 7 8 9))
(trail T) )
-> (A 1 D 8)
or, in the equivalent form,
(let (((A) NIL NIL D) '((1 2 3) (4 5 6) 7 8 9))
(trail T) )
-> (A 1 D 8)
♪♫ Alex
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