Issue with define-type and typed classes

[hashim muqtadir]

So I have this file, found here: https://gitlab.com/hashimmm/remap/-/blob/3682db9fff3bc5007833e07bf9a9ed6e8e0170a9/private/tables.rkt

Lines 51 through 55 say:

(define-type (Func<%> A)
  (BaseFunc<%> A FuncAnyParam))

(define-type BoolFunc<%> (Func<%> BooleanColumn))
(define-type AnyFunc<%> (Func<%> ColIdent))


And this used to work on older versions of racket, say Racket BC 7.4

But on Racket CS 7.6, I get an error on this line: 
(define-type AnyFunc<%> (Func<%> ColIdent))

Even though (a) it doesn't throw an error on the line before it, and
(b) replacing it with (define-type AnyFunc<%> (BaseFunc<%> ColIdent FuncAnyParam))
works.

I thought the way define-type works is that 
(Func<%> ColIdent)
would expand into (BaseFunc<%> ColIdent FuncAnyParam)

I've had similar problems with define-type previously where I'd think it would just expand
by substituting the parameter but it doesn't seem to really do that. I don't have any
trivial example to show, though. Fiddling around eventually gets it to work.

I'd really appreciate some help as to how to think about what define-type does in my head.

[Ben Greenman]

On 3/5/20, hashim muqtadir <hashim....@gmail.com> wrote:
> So I have this file, found here:
> https://gitlab.com/hashimmm/remap/-/blob/3682db9fff3bc5007833e07bf9a9ed6e8e0170a9/private/tables.rkt
>
> Lines 51 through 55 say:
>
> (define-type (Func<%> A) (BaseFunc<%> A FuncAnyParam))(define-type

> BoolFunc<%> (Func<%> BooleanColumn))(define-type AnyFunc<%> (Func<%>

> ColIdent))
>
> And this used to work on older versions of racket, say Racket BC 7.4
>
> But on Racket CS 7.6, I get an error on this line:
> (define-type AnyFunc<%> (Func<%> ColIdent))
>
> Even though (a) it doesn't throw an error on the line before it, and
> (b) replacing it with (define-type AnyFunc<%> (BaseFunc<%> ColIdent
> FuncAnyParam))
> works.
>
> I thought the way define-type works is that
> (Func<%> ColIdent)
> would expand into (BaseFunc<%> ColIdent FuncAnyParam)
>
> I've had similar problems with define-type previously where I'd think it
> would just expand
> by substituting the parameter but it doesn't seem to really do that. I don't
> have any
> trivial example to show, though. Fiddling around eventually gets it to
> work.
>
> I'd really appreciate some help as to how to think about what define-type
> does in my head.
>

That code should work. There's a bug somewhere, either TR or deeper.

I am thinking its deeper because the code sometimes compiles.

1. When I first tried `raco pkg install remap` (using a current CS), it worked
2. Then I tried compiling with BC 7.6 and CS 7.6. BC succeeded and CS failed.
3. Later, I saw 2 consecutive runs of CS fail and succeed:

```
(20:02)% rm -r compiled

(20:02)% /Applications/RacketCS-v7.6/bin/raco make -v tables.rkt
"tables.rkt":
making #<path:/Users/ben/code/racket/fork/extra-pkgs/remap/private/tables.rkt>
/Users/ben/code/racket/fork/extra-pkgs/remap/private/tables.rkt:59:3:
Type Checker: parse error in type;
expected a class type for #:implements clause
given: (Opaque Func<%>)
in: (Class #:implements BoolFunc<%>)
compilation context...:
/Users/ben/code/racket/fork/extra-pkgs/remap/private/tables.rkt
context...:
do-raise-syntax-error
winder-dummy
.../private/parse-type.rkt:1234:0: merge-with-parent-type
.../private/parse-type.rkt:1364:14: for-loop
.../private/parse.rkt:852:26
.../private/runtime.rkt:80:24: temp5975
.../env/type-alias-helper.rkt:230:4: for-loop
.../env/type-alias-helper.rkt:101:0: register-all-type-aliases
.../typecheck/tc-toplevel.rkt:359:0: type-check
.../typecheck/tc-toplevel.rkt:602:0: tc-module
.../typed-racket/tc-setup.rkt:96:12
winder-dummy
.../typed-racket/typed-racket.rkt:23:4
call-in-empty-metacontinuation-frame
apply-transformer
dispatch-transformer

(1:20:02)% rm -r compiled
rm: compiled: No such file or directory

(1:20:02)% /Applications/RacketCS-v7.6/bin/raco make -v tables.rkt
"tables.rkt":
making #<path:/Users/ben/code/racket/fork/extra-pkgs/remap/private/tables.rkt>
[output to "compiled/tables_rkt.zo"]
```

[hashim muqtadir]

I am thinking its deeper because the code sometimes compiles.

Yes, this happens with me too. I haven't tried it using raco but in DrRacket, while I

was fiddling around with these classes, it would sometimes fail to compile, but

I just used to erase what I wrote, and then re-write, and it would work.

Once compiled it seemed to work fine.

But I believe they're separate problems.

I'll try to be more diligent about reporting issues with typed classes next time. I used to run into

problems similar to what I reported in this thread previously, too, on whatever version of Racket

was out a year or two ago, but I was throwing away and rewriting code quickly and it

was hard to come up with minimal examples at the time.

This one reproduced very reliably and I wasn't really making big changes so I was able to

report easily.

[Sam Tobin-Hochstadt]

When this happens, it's usually a bug in Typed Racket caused by depending on hash table ordering, so it would be great to find and fix it. 

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