On Fri, Oct 21, 2011 at 12:44 PM, Eric Tanter <etan...@dcc.uchile.cl> wrote: > To come back on this: I understand that Typed Racket's prime objective is > that the type system should adapt to existing programming idioms as much as > possible. But does this prevent new type-related idioms to be used? > > In that sense, union types are a particularly good example. They are > necessary to support the kind of patterns found in previously-untyped code. > But if I'm writing typed code, and I'm using union types, then I'd expect a > case construct based on the type. Sure enough, this won't be code for which I > could just "remove the types".
What would such a construct look like? Forms like `cases' from PLAI work fine in plain Racket. > Or is the Typed Racket philosophy definitely opposed to introducing such > type-only constructs? Some features are definitely typed-language only, such as automatically introducing numeric coercions a la C, or type class dispatch on the annotated return type in Haskell, or static method resolution in Java. I don't currently plan on adding features like this, in large part because it would greatly complicate the interaction between typed and untyped programs. Instead, I think Typed Racket should work with the Racket numeric tower, struct properties, and the Racket class system. So far, I haven't seen any strong reasons why Typed Racket would need to take a different approach. > > Thanks, > > -- Éric > > > On Oct 20, 2011, at 3:39 PM, Sam Tobin-Hochstadt wrote: > >> There are basically two options here: >> >> 1. If you just use `cond' with no `else', you get a type error when >> your cases are not exhaustive. For example: >> >> (: f ((U String Integer) -> Boolean)) >> (define (f x) >> [(string? x) (string=? x "hi")] >> [(exact-nonnegative-integer? x) (= x 7)]) >> >> This program will fail to typecheck. >> >> 2. For the particular case of the PLAI `cases' form, Eli and I have >> built something for his class which uses Typed Racket, but the >> exhaustiveness checking is done by `cases' itself. Lots more about >> that is available from Eli's class web page [1], and I'm sure he'd be >> happy to give you the code. >> >> [1] http://pl.barzilay.org/ >> >> On Thu, Oct 20, 2011 at 10:48 AM, Eric Tanter <etan...@dcc.uchile.cl> wrote: >>> Hi again, >>> >>> Is there a mechanism to do an exhaustive type case? >>> >>> I know I can use (cond [(type-pred? v) ...] >>> [...]) >>> >>> but of course I have no guarantee that I am exhaustive (and of course, >>> doing pattern matching to destruct the value would be even nicer). >>> >>> Basically, I guess I'm after the typed version of PLAI's type-case. >>> >>> Thanks, >>> >>> -- Éric >>> >>> >>> >>> _________________________________________________ >>> For list-related administrative tasks: >>> http://lists.racket-lang.org/listinfo/users >>> >> >> >> >> -- >> sam th >> sa...@ccs.neu.edu >> > > -- sam th sa...@ccs.neu.edu _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
