[racket-dev] In Typed Racket, struct declarations do not work in an internal definition context

From: Alexis King (lexi.lambda at gmail.com)
Date: Thu Jan 22 15:57:21 EST 2015

Simple enough. This works:

#lang racket

(define (make-me-a-struct)
  (struct foo ())

(make-me-a-struct) ; => #<foo>

This does not:

#lang typed/racket

(define (make-me-a-struct)
  (struct foo ())
  (foo)) ; error: cannot apply a function with unknown arity


This problem makes sense. Type declarations seem to be a module-wide construct, so a type that should be scoped to a single function doesn’t work. I’m running into this issue when trying to create an executable struct using define-struct/exec from within a macro, which doesn’t work due to this particular problem.

I can work around this in a variety of ways—I can extract this into an untyped module and use require/typed, I can use vectors to “fake” structs and provide an appropriate interface, etc. Still, I wonder if there are any plans to resolve this type of problem? Since it seems to be an issue with how TR handles types at its core, I’m not even sure how feasible it would be.
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