[racket] Ad-hoc polymorphism in Typed Racket

From: Vincent St-Amour (stamourv at ccs.neu.edu)
Date: Mon Feb 14 16:57:25 EST 2011

At Mon, 14 Feb 2011 16:42:52 +0000,
Noel Welsh wrote:
> What's the story for ad-hoc polymorphism in Racket?

I'm assuming you mean Typed Racket.

For the built-in functions that are currently supported by TR, the
ad-hoc polymorphism should work. If you want to write your own ad-hoc
polymorphic functions, you can give them types constructed with the
case-lambda type constructor (which is not the same thing as Racket's
case-lambda macro):

In git, you can also use case-> as a synonym for case-lambda.

> In particular, I'd
> like to use the dict library.

The dict library is not currently supported. The main problem is that
I'm not aware of a way to express the fact that a (Vectorof X) is a
(Dictof Integer X) in TR's type system, which currently makes dict
operations untypeable. We could give them types that exclude vectors,

Would that be an acceptable solution for you?


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