On 2020-11-14 02:58:44 -0800, [email protected] wrote:
> Any advice on how to make this work? Or whether to simply not do this in
> typed racket?
It's possible to do this in Typed Racket but it's just a bit more
cumbersome as you need to make the function type row-polymorphic. Here's
a version that should typecheck:
;;;
#lang typed/racket/base
(require typed/racket/class)
(define-type recipe<%>
(Class (init [name String])
(get-name (-> String))))
(: recipe% recipe<%>)
(define recipe%
(class object%
(init [name : String])
(super-new)
(: _name String)
(define _name name)
(define/public (get-name) _name)))
(: amount-mixin (All (r #:row)
(-> (Class #:implements recipe<%>
#:row-var r)
(Class #:implements recipe<%>
#:row-var r
(init [amount Number])
(get-amount (-> Number))))))
(define (amount-mixin %)
(class %
(init [amount : Number])
(: _amount Number)
(define _amount amount)
(super-new)
(inherit get-name)
(define/public (get-amount) _amount)))
(: unit-mixin (All (r #:row)
(-> (Class #:implements recipe<%>
#:row-var r)
(Class #:implements recipe<%>
#:row-var r
(init [unit String])
(get-unit (-> String))))))
(define (unit-mixin %)
(class %
(init [unit : String])
(: _unit String)
(define _unit unit)
(super-new)
(inherit get-name)
(define/public (get-unit) _unit)))
(unit-mixin (amount-mixin recipe%))
;;;
Cheers,
Asumu
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