[racket] TR Structure Matching

You can use an `and' pattern:

    (: do-it (Thing -> String))
    (define (do-it thing)
      (match thing
        ((and p [Person fn ln])
         (displayln fn)
         (person-name p))))

Vincent


At Tue, 4 Dec 2012 17:53:57 -0500,
Ray Racine wrote:
> 
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> How does one bind an identifier to the matched structure?
> 
> In SML, Scala one can do something along the lines of s at S (x y z)
> 
> #lang typed/racket
> 
> (struct: Thing ())
> (struct: Person Thing ([fname : String] [lname : String]))
> 
> (: person-name (Person -> String))
> (define (person-name p)
>   (string-append (Person-lname p) ", " (Person-fname p)))
> 
> (define js (Person "Joe" "Smith"))
> 
> (: do-it (Thing -> String))
> (define (do-it thing)
>   (match thing
>     ([Person fn ln]
>      (displayln fn)
>      (person-name thing))))
> 
> This fails as `thing' is not recognized as a Person.
> 
> I guess I'm wondering if there is something along the lines of the
> following in `match'.
> 
> (match thing
>     (p@[Person fn ln]
>      (person-name p)))) ;; p is typed as a Person
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