[racket] JSExprs and hashtables

Since hash-tables can be mutable as far as TR knows, (HashTable Symbol String) is not a subtype of (HashTable Symbol JSExpr).
To work around this, you can do this:
#lang typed/racket/base
(require typed/json)
(: jsx JSExpr)       ; <-- jsx is what I ultimately want.
(define jsx (ann #hasheq((a . "val1") (b . "val2") (c . "val3")) (HashTable Symbol JSExpr)))

Or this would work too:
#lang typed/racket/base
(require typed/json)
(: jsx (HashTable Symbol JSExpr))       ; <-- jsx is what I ultimately want.
(define jsx #hasheq((a . "val1") (b . "val2") (c . "val3")))

Or you could use (inst make-immutable-hasheq Symbol JSExpr) instead of using #hasheq, and it would do the same thing.


On Jan 19, 2015, at 1:28 AM, Jordan Johnson <jmj at fellowhuman.com> wrote:

> Hi all,
> 
> I’ve been trying to create JSExprs, as defined in the typed/json library. This is one of those instances where it seems like I must be making things harder than they should be, but I’m still feeling like a duck on rollerskates in TR, so I want to make sure I’m not missing an easier way to do it.
> 
> Would you please confirm if this is indeed a smallest-possible solution?
> 
> ;;;; begin
> #lang typed/racket/base
> 
> (require typed/json)
> 
> (: jsx JSExpr)       ; <-- jsx is what I ultimately want.
> 
> ;; Attempt #1:
> #;
> (define jsx #hasheq((a . "val1") (b . "val2") (c . "val3")))
> 
> #| Resulting error:
> Type Checker: type mismatch
>   expected: JSExpr
>   given: (HashTable Symbol String)
> 
> [This seems weird, since it seems like (HashTable Symbol String) should be
>  a subtype of JSExpr. Is the problem that the typechecker can’t recognize
>  the Strings as JSExprs?]
> |#
> 
> ;; Attempt #N (shortest successful version I’ve found):
> (define jsx
>   (for/hasheq : (HashTable Symbol JSExpr) ([k '(a b c)]
>                                            [v '("val1" "val2" "val3")])
>     (values k v)))
> ;;;; end
> 
> Regards,
> Jordan
> 
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>  http://lists.racket-lang.org/users

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