Here’s a simple program that fails:
#lang typed/racket
(define (obscurinator [x : Any]) : Any
x)
(struct PrimV ([f : (Real Real -> Real)]) #:transparent)
(define dangerval : PrimV
(cast (obscurinator (PrimV +))
PrimV))
((PrimV-f dangerval) 3 4)
It type-checks fine, but it produces this error in 6.8.0.2--2017-01-19(-/f)
[3m].:
contract violation
Attempted to use a higher-order value passed as `Any` in untyped code:
#<procedure:+>
in: Any
contract from: typed-world
blaming: cast
(assuming the contract is correct)
at: unsaved-editor:9.2
Basically, the ‘cast’ to a higher-order value type creates a time bomb that
blows up when called. Is this a bug?
More generally, how do we feel about a type system that appears to introduce
run-time errors into otherwise correct programs? I think it might be nicer just
to prevent casts to higher-order types than to introduce this kind of time bomb
(pardon the excessively pejorative term). Apologies if I’m misunderstanding
this. Or maybe this is a fixable bug in TR?
At a minimum, explaining it to a class of Java programmers is going to be
interesting.
John
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