In this context, null is just a variable and it gets bound to what it matches:
> Welcome to Racket v6.1.0.8. > > (match 'hello-world [null null]) > 'hello-world On Oct 1, 2014, at 4:52 PM, Yuri Garmay <yuri.from....@gmail.com> wrote: > Hi, all > > Accidentally, I found out that null matchs in unexpected way (seems it matchs > always) > > So, > (define (length-my list) > (match list > ['() 0] > [(cons x xs) > (+ 1 > (length-my xs))] > [_ 'not-a-list])) > (length-my '(1 2 3 4)) > >produces 4 > > But > (define (length-my list) > (match list > [null 0] > [(cons x xs) > (+ 1 > (length-my xs))] > [_ 'not-a-list])) > (length-my '(1 2 3 4)) > >produces 0 > > I also tried that: > (match '213423 > [null 0] > [_ 1]) > >produces 0 > (match null > ['213423 0] > [_ 1]) > >produces 1 > > Is it a bug? > > I am using Racket 6.1 > > -- > Best regards, > Yuri > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
