IIRC, one of your ideas was to expand module code to a typed and an
untyped submodule, and have them provide the same identifiers. Somehow -
doesn't matter exactly for now - untyped clients would get the untyped
identifiers, and typed clients would get the typed identifiers.
I've had some experience doing something similar with macros. A good
example is the `in-array' macro, defined in
"math/private/array/array-sequence.rkt". Here's part of the expansion of
(in-array arr-expr):
(plet: (A) ([arr : (Array A) arr-expr])
(cond [(array? arr)
(define ds (array-shape arr))
(define dims (vector-length ds))
(define size (array-size arr))
(define proc (unsafe-array-proc arr))
(define: js : Indexes (make-vector dims 0))
(values ds size dims js proc)]
[else
(raise-argument-error 'in-array "Array" arr)]))
It's kind of annoying to have to keep in mind that the macro will be
expanded in both typed and untyped contexts. In this case - and this is
pretty typical - the expanded code has to ensure that it gets an array
in two different ways. One is (plet: (A) ([arr : (Array A) arr-expr])
...) for Typed Racket. The other is (cond [(array? arr) ...] [else ...])
for untyped Racket.
One sort of nice thing is that TR's optimizer erases the `else' branch.
I don't think it can erase the expression (array? arr), though. Also,
the type annotations mean nothing in untyped Racket, so it's kind of
like they get erased.
I could see writing a few modules like this, especially with help from
some good macros.
The thing I worry about most is that a struct type would have two
different definitions, typed and untyped, which would be different
struct types at run time. In particular, an array created in a Typed
Racket client couldn't be sent to an array-accepting function defined in
an untyped client. That seems like a deal-breaker, and I can't think of
an easy way around it.
Neil ⊥
On 12/17/2012 06:34 PM, Matthias Felleisen wrote:
Begin forwarded message:
From: Matthias Felleisen <matth...@ccs.neu.edu>
Subject: Re: [racket-dev] Typed versions of untyped collections
Date: December 17, 2012 6:44:19 PM EST
To: Neil Toronto <neil.toro...@gmail.com>
Cc: dev@racket-lang.org
Okay. I propose we figure out how to allow people programming in Typed Racket,
and deploy two copies of the code without performance overhead for either T or U
code.
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