[plt-scheme] Another pattern puzzle

[Matthew Flatt]

At Thu, 15 Nov 2007 13:41:11 +0100, Jens Axel Soegaard wrote:
> An identifier matches a list pattern:
> 
>    > (syntax-case #'x ()
>        [(a ... . more) 'huh?]
>        [_              'ok])
> 
>    huh?

It's not really a "list" pattern, though; it matches N chained cons
cells ending with something that matches `more', and `more' isn't
required to be a list.

So, #'x matches a chain of 0 cons cells ending with a match to `more'.

A related example:

 > (syntax-case #'(1 . 2) () 
     [(a ... . more) (syntax->datum #'more)])
 2
 > (syntax-case #'(1 1 1 1 . 2) () 
     [(a ... . more) (syntax->datum #'more)])
 2
 > (syntax-case #'2 () 
     [(a ... . more) (syntax->datum #'more)])
 2

Matthew