It looks to me like TR can’t generate contracts for prefab structs in a way
that I would expect it to. Specifically, here’s a TR file and a Racket file
that uses a TR-defined prefab structure:
makes-foo.rkt:
#lang typed/racket
(provide (struct-out Foo)
get-a-foo)
(struct Foo ([a : String]) #:prefab)
(define (get-a-foo)
(Foo "oeuth”))
uses-foo.rkt:
#lang racket
(require "makes-foo.rkt")
(define a (get-a-foo))
This doesn’t typecheck (at least not in version 6.11.0.2--2017-11-05, tell me
if I should just upgrade), with the message:
Type Checker: could not convert type to a contract;
contract generation not supported for this type
identifier: get-a-foo
type: (-> Foo) in: (get-a-foo)
My first thought was that this was related to mutability, but the docs and my
experiments suggest that prefab structures are default-immutable, and that this
is reflected in a way that should be visible to the type-checker. Am I missing
something, or is this just something that we haven’t yet had time to implement?
John
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