Re: [racket-users] hash-ref in typed Racket

[Sam Tobin-Hochstadt]

That particular pattern, with `(U String (-> String))`, will work, but
your generalized version would be wrong if it worked. Consider:

```
(: unsound : (Immutable-HashTable Symbol (-> String)) -> String)
(define (unsound h)
  ((hash-ref h (gensym) (lambda () "x"

(unsound (hash))
```

This program type checks with your second `require/typed` of
`hash-ref`, but it's wrong. We can see that by using
`unsafe-require/typed`, and we get an error because we can't apply
"x".

Furthermore, you can't generalize to (U T (-> T) either, because if T
is (-> String) then you get the same problem.

Sam

On Wed, Nov 25, 2020 at 7:28 AM Tim Jervis  wrote:
>
> For the record, this seems to work fine:
>
> #lang typed/racket
>
> (require/typed racket
>   [hash-ref ((Immutable-HashTable Symbol
>   (U (-> String)
>  String))
>  Symbol
>  (U String
> (-> String))
>  ->
>  (U String
> (-> String)))])
>
> (let* ([h : (Immutable-HashTable Symbol
>  (U (-> String)
> String))
>   (make-immutable-hash)]
>[h (hash-set h
> 'function
> (thunk "Function value"))]
>[h (hash-set h
> 'string
> "String value")])
>
>   (printf "Fixed string on error:\n")
>   (for ([key (in-list '(function string missing))])
> (printf "key: ~a\tvalue: ~a\n"
> key
> (hash-ref h
>   key
>   "Missed!")))
>   (printf "\n")
>
>   (printf "Thunk on error:\n")
>   (for ([key (in-list '(function string missing))])
> (printf "key: ~a\tvalue: ~a\n"
> key
> (hash-ref h
>   key
>   (thunk "Missed!")
>
>
>
>
> >
> Fixed string on error:
> key: function value: # key: string value: String value
> key: missing value: Missed!
>
> Thunk on error:
> key: function value: # key: string value: String value
> key: missing value: Missed!
>
>
>
>
>
>
> but this attempt to generalise fails:
>
> #lang typed/racket
>
> (require/typed racket
>   [hash-ref (All (K V)
>  (Immutable-HashTable K V)
>  K
>  V
>  ->
>  V)])
>
> (let* ([h : (Immutable-HashTable Symbol
>  (U (-> String)
> String))
>   (make-immutable-hash)]
>[h (hash-set h
> 'function
> (thunk "Function value"))]
>[h (hash-set h
> 'string
> "String value")])
>
>   (printf "Fixed string on error:\n")
>   (for ([key (in-list '(function string missing))])
> (printf "key: ~a\tvalue: ~a\n"
> key
> (hash-ref h
>   key
>   "Missed!")))
>   (printf "\n")
>
>   (printf "Thunk on error:\n")
>   (for ([key (in-list '(function string missing))])
> (printf "key: ~a\tvalue: ~a\n"
> key
> (hash-ref h
>   key
>   (thunk "Missed!")
>
>
>
> >
> ; hash/c: contract violation
> ;   expected: chaperone-contract?
> ;   given: K4
>
>
> On 24 Nov 2020, at 15:20, Tim Jervis  wrote:
>
> Wouldn’t that possibility then have to be part of the type for the values in 
> the hash? Maybe I don’t understand how types work for hashes.
>
> In this code:
>
> #lang typed/racket
>
> (define h : (Immutable-HashTable Integer (-> String))
>   (make-immutable-hash))
>
> (hash-ref h
>   2
>   (thunk "Hit and miss"))
>
>
> I think I’ve set the type of the values of the hash h to be a thunk that 
> returns a string. I’m then trying to access a key in that hash, which misses 
> because the hash has no keys. The third argument works because it’s a 
> function that happens to return a string. It’s funny because it looks like it 
> type-checks, but it doesn’t really.
>
> This code:
>
> #lang typed/racket
>
> (define h : (Immutable-HashTable Integer String)
>   (make-immutable-hash))
>
> (hash-ref h
>   2
>   (thunk "Hit and miss"))
>
>
> also type-checks because even though the third argument to hash-ref is not a 
> String, it is a function.
>
> Oddly, to me at least,
>
> #lang typed/racket
>
> (define h : (Immutable-HashTable Integer String)
>   (make-immutable-hash))
>
> (hash-ref h
>   2
>   "Hit and miss")
>
>
> Does not type check even though the type of the hash’s values is String, the 
> same as the third argument of hash-ref.
>
> On 24 Nov 2020, at 14:44, Sam Tobin-Hochstadt  wrote:
>
> Unfortunately, that doesn't work -- the values in the hash could
> include functions.
>
> Sam
>
> On Tue, Nov 24, 2020 at 7:25 AM Tim Jervis  wrote:
>
>
> For the type of the third argument, rather than "any non-function", could 
> Typed Racket use the type of the va

Re: [racket-users] hash-ref in typed Racket

[Tim Jervis]

For the record, this seems to work fine:

#lang typed/racket

(require/typed racket
  [hash-ref ((Immutable-HashTable Symbol 
  (U (-> String)
 String))
 Symbol
 (U String
(-> String))
 ->
 (U String
(-> String)))])

(let* ([h : (Immutable-HashTable Symbol 
 (U (-> String)
String))
  (make-immutable-hash)]
   [h (hash-set h
'function
(thunk "Function value"))]
   [h (hash-set h
'string
"String value")])

  (printf "Fixed string on error:\n")
  (for ([key (in-list '(function string missing))])
(printf "key: ~a\tvalue: ~a\n"
key
(hash-ref h
  key
  "Missed!")))
  (printf "\n")

  (printf "Thunk on error:\n")
  (for ([key (in-list '(function string missing))])
(printf "key: ~a\tvalue: ~a\n"
key
(hash-ref h
  key
  (thunk "Missed!")



>
Fixed string on error:
key: function   value: #
 V)])

(let* ([h : (Immutable-HashTable Symbol
 (U (-> String)
String))
  (make-immutable-hash)]
   [h (hash-set h
'function
(thunk "Function value"))]
   [h (hash-set h
'string
"String value")])

  (printf "Fixed string on error:\n")
  (for ([key (in-list '(function string missing))])
(printf "key: ~a\tvalue: ~a\n"
key
(hash-ref h
  key
  "Missed!")))
  (printf "\n")

  (printf "Thunk on error:\n")
  (for ([key (in-list '(function string missing))])
(printf "key: ~a\tvalue: ~a\n"
key
(hash-ref h
  key
  (thunk "Missed!")


>
; hash/c: contract violation
;   expected: chaperone-contract?
;   given: K4

> On 24 Nov 2020, at 15:20, Tim Jervis  wrote:
> 
> Wouldn’t that possibility then have to be part of the type for the values in 
> the hash? Maybe I don’t understand how types work for hashes.
> 
> In this code:
> 
> #lang typed/racket
> 
> (define h : (Immutable-HashTable Integer (-> String))
>   (make-immutable-hash))
> 
> (hash-ref h
>   2
>   (thunk "Hit and miss"))
> 
> I think I’ve set the type of the values of the hash h to be a thunk that 
> returns a string. I’m then trying to access a key in that hash, which misses 
> because the hash has no keys. The third argument works because it’s a 
> function that happens to return a string. It’s funny because it looks like it 
> type-checks, but it doesn’t really.
> 
> This code:
> 
> #lang typed/racket
> 
> (define h : (Immutable-HashTable Integer String)
>   (make-immutable-hash))
> 
> (hash-ref h
>   2
>   (thunk "Hit and miss"))
> 
> also type-checks because even though the third argument to hash-ref is not a 
> String, it is a function.
> 
> Oddly, to me at least,
> 
> #lang typed/racket
> 
> (define h : (Immutable-HashTable Integer String)
>   (make-immutable-hash))
> 
> (hash-ref h
>   2
>   "Hit and miss")
> 
> Does not type check even though the type of the hash’s values is String, the 
> same as the third argument of hash-ref.
> 
>> On 24 Nov 2020, at 14:44, Sam Tobin-Hochstadt > > wrote:
>> 
>> Unfortunately, that doesn't work -- the values in the hash could
>> include functions.
>> 
>> Sam
>> 
>> On Tue, Nov 24, 2020 at 7:25 AM Tim Jervis > > wrote:
>>> 
>>> For the type of the third argument, rather than "any non-function", could 
>>> Typed Racket use the type of the values in the hash?
>>> 
>>> On Tuesday, 21 April 2020 at 15:51:00 UTC+1 Sam Tobin-Hochstadt wrote:
 
 The problem here is with the optional third argument to `hash-ref`.
 Typed Racket only allows `#f` or functions as the third argument.
 Plain Racket allows any non-function value as a default, or a function
 which is called to produce the default. Since "any non-function" is
 not expressible in Typed Racket, it's more restricted here.
 
 The best option is to wrap the third argument in a thunk: `(lambda () 
 'other)`.
 
 As an aside, you probably don't want to use `cast` this extensively in
 your program.
 
 Sam
 
 On Tue, Apr 21, 2020 at 10:35 AM Hendrik Boom >>> > wrote:
> 
> In typed Racket I define a hashtable:
> 
> (: vector-to-contract (HashTable TType CContract))
> 
> (define vector-to-contract
> (make-hash
> (cast '(
> (_bytes . bytes?)
> (_s8vector . s8vector?)
> (_u16vector . u16vector?)
> (_s16vecto

Re: [racket-users] hash-ref in typed Racket

[Tim Jervis]

Wouldn’t that possibility then have to be part of the type for the values in 
the hash? Maybe I don’t understand how types work for hashes.

In this code:

#lang typed/racket

(define h : (Immutable-HashTable Integer (-> String))
  (make-immutable-hash))

(hash-ref h
  2
  (thunk "Hit and miss"))

I think I’ve set the type of the values of the hash h to be a thunk that 
returns a string. I’m then trying to access a key in that hash, which misses 
because the hash has no keys. The third argument works because it’s a function 
that happens to return a string. It’s funny because it looks like it 
type-checks, but it doesn’t really.

This code:

#lang typed/racket

(define h : (Immutable-HashTable Integer String)
  (make-immutable-hash))

(hash-ref h
  2
  (thunk "Hit and miss"))

also type-checks because even though the third argument to hash-ref is not a 
String, it is a function.

Oddly, to me at least,

#lang typed/racket

(define h : (Immutable-HashTable Integer String)
  (make-immutable-hash))

(hash-ref h
  2
  "Hit and miss")

Does not type check even though the type of the hash’s values is String, the 
same as the third argument of hash-ref.

> On 24 Nov 2020, at 14:44, Sam Tobin-Hochstadt  wrote:
> 
> Unfortunately, that doesn't work -- the values in the hash could
> include functions.
> 
> Sam
> 
> On Tue, Nov 24, 2020 at 7:25 AM Tim Jervis  wrote:
>> 
>> For the type of the third argument, rather than "any non-function", could 
>> Typed Racket use the type of the values in the hash?
>> 
>> On Tuesday, 21 April 2020 at 15:51:00 UTC+1 Sam Tobin-Hochstadt wrote:
>>> 
>>> The problem here is with the optional third argument to `hash-ref`.
>>> Typed Racket only allows `#f` or functions as the third argument.
>>> Plain Racket allows any non-function value as a default, or a function
>>> which is called to produce the default. Since "any non-function" is
>>> not expressible in Typed Racket, it's more restricted here.
>>> 
>>> The best option is to wrap the third argument in a thunk: `(lambda () 
>>> 'other)`.
>>> 
>>> As an aside, you probably don't want to use `cast` this extensively in
>>> your program.
>>> 
>>> Sam
>>> 
>>> On Tue, Apr 21, 2020 at 10:35 AM Hendrik Boom  wrote:
 
 In typed Racket I define a hashtable:
 
 (: vector-to-contract (HashTable TType CContract))
 
 (define vector-to-contract
 (make-hash
 (cast '(
 (_bytes . bytes?)
 (_s8vector . s8vector?)
 (_u16vector . u16vector?)
 (_s16vector . s16vector?)
 (_u32vector . u32vector?)
 (_s32vector . s32vector?)
 (_u64vector . u64vector?)
 (_s64vector . s64vector?)
 (_f32vector . f32vector?)
 (_f64vector . f64vector?))
 (Listof (Pair TType CContract))
 )
 ))
 
 And then I try to look something up in it:
 
 ( hash-ref vector-to-contract (cast '_bytes TType) (cast 'other CContract))
 
 and I am informed that I cannot, it seems, look up a value of type
 TType in a hastable whose type indicates it looks up things of type
 TType:
 
 Type Checker: Polymorphic function `hash-ref' could not be applied to 
 arguments:
 Types: HashTableTop a (-> c) -> Any
 HashTableTop a False -> Any
 HashTableTop a -> Any
 Arguments: (HashTable TType CContract) TType CContract
 Expected result: AnyValues
 in: (hash-ref vector-to-contract (cast (quote _bytes) TType) (cast
 (quote other) CContract))
 
 
 How *does* one use hashtables in typed Racket?
 
 -- hendrik
 
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Re: [racket-users] hash-ref in typed Racket

[Sam Tobin-Hochstadt]

Unfortunately, that doesn't work -- the values in the hash could
include functions.

Sam

On Tue, Nov 24, 2020 at 7:25 AM Tim Jervis  wrote:
>
> For the type of the third argument, rather than "any non-function", could 
> Typed Racket use the type of the values in the hash?
>
> On Tuesday, 21 April 2020 at 15:51:00 UTC+1 Sam Tobin-Hochstadt wrote:
>>
>> The problem here is with the optional third argument to `hash-ref`.
>> Typed Racket only allows `#f` or functions as the third argument.
>> Plain Racket allows any non-function value as a default, or a function
>> which is called to produce the default. Since "any non-function" is
>> not expressible in Typed Racket, it's more restricted here.
>>
>> The best option is to wrap the third argument in a thunk: `(lambda () 
>> 'other)`.
>>
>> As an aside, you probably don't want to use `cast` this extensively in
>> your program.
>>
>> Sam
>>
>> On Tue, Apr 21, 2020 at 10:35 AM Hendrik Boom  wrote:
>> >
>> > In typed Racket I define a hashtable:
>> >
>> > (: vector-to-contract (HashTable TType CContract))
>> >
>> > (define vector-to-contract
>> > (make-hash
>> > (cast '(
>> > (_bytes . bytes?)
>> > (_s8vector . s8vector?)
>> > (_u16vector . u16vector?)
>> > (_s16vector . s16vector?)
>> > (_u32vector . u32vector?)
>> > (_s32vector . s32vector?)
>> > (_u64vector . u64vector?)
>> > (_s64vector . s64vector?)
>> > (_f32vector . f32vector?)
>> > (_f64vector . f64vector?))
>> > (Listof (Pair TType CContract))
>> > )
>> > ))
>> >
>> > And then I try to look something up in it:
>> >
>> > ( hash-ref vector-to-contract (cast '_bytes TType) (cast 'other CContract))
>> >
>> > and I am informed that I cannot, it seems, look up a value of type
>> > TType in a hastable whose type indicates it looks up things of type
>> > TType:
>> >
>> > Type Checker: Polymorphic function `hash-ref' could not be applied to 
>> > arguments:
>> > Types: HashTableTop a (-> c) -> Any
>> > HashTableTop a False -> Any
>> > HashTableTop a -> Any
>> > Arguments: (HashTable TType CContract) TType CContract
>> > Expected result: AnyValues
>> > in: (hash-ref vector-to-contract (cast (quote _bytes) TType) (cast
>> > (quote other) CContract))
>> >
>> >
>> > How *does* one use hashtables in typed Racket?
>> >
>> > -- hendrik
>> >
>> > --
>> > You received this message because you are subscribed to the Google Groups 
>> > "Racket Users" group.
>> > To unsubscribe from this group and stop receiving emails from it, send an 
>> > email to racket-users...@googlegroups.com.
>> > To view this discussion on the web visit 
>> > https://groups.google.com/d/msgid/racket-users/20200421143453.lauuqi3pb4fdgyhh%40topoi.pooq.com.
>
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Re: [racket-users] hash-ref in typed Racket

[Tim Jervis]

For the type of the third argument, rather than "any non-function", could 
Typed Racket use the type of the values in the hash?

On Tuesday, 21 April 2020 at 15:51:00 UTC+1 Sam Tobin-Hochstadt wrote:

> The problem here is with the optional third argument to `hash-ref`.
> Typed Racket only allows `#f` or functions as the third argument.
> Plain Racket allows any non-function value as a default, or a function
> which is called to produce the default. Since "any non-function" is
> not expressible in Typed Racket, it's more restricted here.
>
> The best option is to wrap the third argument in a thunk: `(lambda () 
> 'other)`.
>
> As an aside, you probably don't want to use `cast` this extensively in
> your program.
>
> Sam
>
> On Tue, Apr 21, 2020 at 10:35 AM Hendrik Boom  
> wrote:
> >
> > In typed Racket I define a hashtable:
> >
> > (: vector-to-contract (HashTable TType CContract))
> >
> > (define vector-to-contract
> > (make-hash
> > (cast '(
> > (_bytes . bytes?)
> > (_s8vector . s8vector?)
> > (_u16vector . u16vector?)
> > (_s16vector . s16vector?)
> > (_u32vector . u32vector?)
> > (_s32vector . s32vector?)
> > (_u64vector . u64vector?)
> > (_s64vector . s64vector?)
> > (_f32vector . f32vector?)
> > (_f64vector . f64vector?))
> > (Listof (Pair TType CContract))
> > )
> > ))
> >
> > And then I try to look something up in it:
> >
> > ( hash-ref vector-to-contract (cast '_bytes TType) (cast 'other 
> CContract))
> >
> > and I am informed that I cannot, it seems, look up a value of type
> > TType in a hastable whose type indicates it looks up things of type
> > TType:
> >
> > Type Checker: Polymorphic function `hash-ref' could not be applied to 
> arguments:
> > Types: HashTableTop a (-> c) -> Any
> > HashTableTop a False -> Any
> > HashTableTop a -> Any
> > Arguments: (HashTable TType CContract) TType CContract
> > Expected result: AnyValues
> > in: (hash-ref vector-to-contract (cast (quote _bytes) TType) (cast
> > (quote other) CContract))
> >
> >
> > How *does* one use hashtables in typed Racket?
> >
> > -- hendrik
> >
> > --
> > You received this message because you are subscribed to the Google 
> Groups "Racket Users" group.
> > To unsubscribe from this group and stop receiving emails from it, send 
> an email to racket-users...@googlegroups.com.
> > To view this discussion on the web visit 
> https://groups.google.com/d/msgid/racket-users/20200421143453.lauuqi3pb4fdgyhh%40topoi.pooq.com
> .
>

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Re: [racket-users] hash-ref in typed Racket

[Hendrik Boom]

On Tue, Apr 21, 2020 at 10:50:44AM -0400, Sam Tobin-Hochstadt wrote:
> The problem here is with the optional third argument to `hash-ref`.
> Typed Racket only allows `#f` or functions as the third argument.
> Plain Racket allows any non-function value as a default, or a function
> which is called to produce the default. Since "any non-function" is
> not expressible in Typed Racket, it's more restricted here.

I missed that.  Thanks.

> 
> The best option is to wrap the third argument in a thunk: `(lambda () 
> 'other)`.
> 
> As an aside, you probably don't want to use `cast` this extensively in
> your program.

No, I don't.  I hoped it would help, but I was fixing the wrong problem, 
so it didn't .

-- hendrik

> 
> Sam
> 
> On Tue, Apr 21, 2020 at 10:35 AM Hendrik Boom  wrote:
> >
> > In typed Racket I define a hashtable:
> >
> > (: vector-to-contract (HashTable TType CContract))
> >
> > (define vector-to-contract
> >   (make-hash
> >(cast '(
> >(_bytes . bytes?)
> >(_s8vector . s8vector?)
> >(_u16vector . u16vector?)
> >(_s16vector . s16vector?)
> >(_u32vector . u32vector?)
> >(_s32vector . s32vector?)
> >(_u64vector . u64vector?)
> >(_s64vector . s64vector?)
> >(_f32vector . f32vector?)
> >(_f64vector . f64vector?))
> >  (Listof (Pair TType CContract))
> >  )
> >))
> >
> > And then I try to look something up in it:
> >
> > ( hash-ref vector-to-contract (cast '_bytes TType) (cast 'other CContract))
> >
> > and I am informed that I cannot, it seems, look up a value of type
> > TType in a hastable whose type indicates it looks up things of type
> > TType:
> >
> > Type Checker: Polymorphic function `hash-ref' could not be applied to 
> > arguments:
> > Types: HashTableTop a (-> c) -> Any
> >HashTableTop a False -> Any
> >HashTableTop a -> Any
> > Arguments: (HashTable TType CContract) TType CContract
> > Expected result: AnyValues
> >  in: (hash-ref vector-to-contract (cast (quote _bytes) TType) (cast
> > (quote other) CContract))
> >
> >
> > How *does* one use hashtables in typed Racket?
> >
> > -- hendrik
> >
> > --
> > You received this message because you are subscribed to the Google Groups 
> > "Racket Users" group.
> > To unsubscribe from this group and stop receiving emails from it, send an 
> > email to racket-users+unsubscr...@googlegroups.com.
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> 
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Re: [racket-users] hash-ref in typed Racket

[Sam Tobin-Hochstadt]

The problem here is with the optional third argument to `hash-ref`.
Typed Racket only allows `#f` or functions as the third argument.
Plain Racket allows any non-function value as a default, or a function
which is called to produce the default. Since "any non-function" is
not expressible in Typed Racket, it's more restricted here.

The best option is to wrap the third argument in a thunk: `(lambda () 'other)`.

As an aside, you probably don't want to use `cast` this extensively in
your program.

Sam

On Tue, Apr 21, 2020 at 10:35 AM Hendrik Boom  wrote:
>
> In typed Racket I define a hashtable:
>
> (: vector-to-contract (HashTable TType CContract))
>
> (define vector-to-contract
>   (make-hash
>(cast '(
>(_bytes . bytes?)
>(_s8vector . s8vector?)
>(_u16vector . u16vector?)
>(_s16vector . s16vector?)
>(_u32vector . u32vector?)
>(_s32vector . s32vector?)
>(_u64vector . u64vector?)
>(_s64vector . s64vector?)
>(_f32vector . f32vector?)
>(_f64vector . f64vector?))
>  (Listof (Pair TType CContract))
>  )
>))
>
> And then I try to look something up in it:
>
> ( hash-ref vector-to-contract (cast '_bytes TType) (cast 'other CContract))
>
> and I am informed that I cannot, it seems, look up a value of type
> TType in a hastable whose type indicates it looks up things of type
> TType:
>
> Type Checker: Polymorphic function `hash-ref' could not be applied to 
> arguments:
> Types: HashTableTop a (-> c) -> Any
>HashTableTop a False -> Any
>HashTableTop a -> Any
> Arguments: (HashTable TType CContract) TType CContract
> Expected result: AnyValues
>  in: (hash-ref vector-to-contract (cast (quote _bytes) TType) (cast
> (quote other) CContract))
>
>
> How *does* one use hashtables in typed Racket?
>
> -- hendrik
>
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[racket-users] hash-ref in typed Racket

[Hendrik Boom]

In typed Racket I define a hashtable:

(: vector-to-contract (HashTable TType CContract))

(define vector-to-contract
  (make-hash
   (cast '(
   (_bytes . bytes?)
   (_s8vector . s8vector?)
   (_u16vector . u16vector?)
   (_s16vector . s16vector?)
   (_u32vector . u32vector?)
   (_s32vector . s32vector?)
   (_u64vector . u64vector?)
   (_s64vector . s64vector?)
   (_f32vector . f32vector?)
   (_f64vector . f64vector?))
 (Listof (Pair TType CContract))
 )
   ))

And then I try to look something up in it:

( hash-ref vector-to-contract (cast '_bytes TType) (cast 'other CContract))

and I am informed that I cannot, it seems, look up a value of type 
TType in a hastable whose type indicates it looks up things of type 
TType:

Type Checker: Polymorphic function `hash-ref' could not be applied to arguments:
Types: HashTableTop a (-> c) -> Any
   HashTableTop a False -> Any
   HashTableTop a -> Any
Arguments: (HashTable TType CContract) TType CContract
Expected result: AnyValues
 in: (hash-ref vector-to-contract (cast (quote _bytes) TType) (cast 
(quote other) CContract))


How *does* one use hashtables in typed Racket?

-- hendrik

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