Greetings, again.
On 2013 Feb 21, at 19:34, Norman Gray <[email protected]> wrote:
> It might also be worth looking at the docs for 'lambda:', since I can't see
> any way of adding keywords to an anonymous function.
...and following up with tangent to my own question, it appears that
make-keyword-procedure and keyword-apply don't work well with Typed Racket.
Consider:
(define make-null
(let ((proc values))
(make-keyword-procedure
(λ (kws kw-args)
(keyword-apply proc kws kw-args '(null))))))
(make-null)
With '#lang racket' that works fine, and prints 'null.
With '#lang typed/racket', however, it produces:
Welcome to DrRacket, version 5.3.3 [3m].
Language: typed/racket; memory limit: 128 MB.
. Type Checker: untyped identifier make-keyword-procedure imported from module
<typed/racket> in: make-keyword-procedure
. Type Checker: untyped identifier keyword-apply imported from module
<typed/racket> in: keyword-apply
. Type Checker: Summary: 2 errors encountered in:
make-keyword-procedure
keyword-apply
>
This is part of an effort to produce a procedure which returns a (anonymous)
procedure within Typed Racket. Now, I'm not sure what the type of
make-keyword-procedure would be, so I'm not sure if this is a sensible thing to
want.
But I'm now quite securely stuck, I think.
----
In case anyone is curious (and in case the clear and obvious solution is indeed
clear and obvious), what I'm trying to do is produce a typed version of the
procedure below:
#lang racket
(struct asn-value (tag ; integer
rep ; symbol or string
type) ; integer in (0--30)
#:transparent)
(define (make-asn-value-maker type-tag)
(define (make-asn-value* tag rep type)
(asn-value tag rep type))
(make-keyword-procedure
(λ (kws kw-args rep)
(let loop ((k kws)
(v kw-args)
(tag 0))
(cond ((null? k)
(make-asn-value* tag rep type-tag))
(else
(let ((class-offset
(case (car k)
((#:application) #x40)
((#:context) #x80)
((#:private) #xc0)
(else (error 'der-codec "asn-value constructor:
unrecognised keyword: ~s" (car k))))))
(unless (= tag 0)
(error 'der-codec "Multiple class keywords in
asn-value-maker: ~s" kws))
(loop (cdr k) (cdr v) (+ class-offset (car v))))))))
(λ (rep)
(make-asn-value* type-tag rep type-tag))))
(define make0 (make-asn-value-maker 0))
(make0 'first) ; => (asn-value 0 'first 0)
(make0 'second #:application 1) ; => (asn-value 65 'second 0)
;(make0 'third #:context 2 #:private 3) ; should error
(and in case anyone's wondering about the keyword names, yes, I am indeed
trying to tidy up a DER encoding/decoding library, which works, but which could
be improved by typification)
Best wishes,
Norman
--
Norman Gray : http://nxg.me.uk
SUPA School of Physics and Astronomy, University of Glasgow, UK
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