[racket] how to define-predicate for a recursive type?

[Erik Silkensen]

Hi,

The code 

#lang typed/racket

(define-type IntList (Rec List (Pair Integer (U List Null))))
(define-predicate int-list? IntList)

> (int-list? '(1 2 3))

gives the runtime error: 

recursive-contract: expected a flat contract or a value that can be coerced 
into one, got #<impersonator-recursive-contract>

Is there a way to generate a predicate for a type like this?

Thanks,
Erik
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