[racket] TR Keyword Args (Lil Help)

From: Neil Toronto (neil.toronto at gmail.com)
Date: Fri Aug 10 15:00:48 EDT 2012

On 08/10/2012 11:54 AM, Sam Tobin-Hochstadt wrote:
> On Fri, Aug 10, 2012 at 1:38 PM, Ray Racine <ray.racine at gmail.com> wrote:
>> Here https://gist.github.com/3315984
>> The first (test1) works fine.  Note it uses a KW arg.
>> However, (test2) fails.  I thought it was the complexity of the first arg
>> that I was getting wrong.  But when the KW #:label is commented out it works
>> fine.
> What's happening here is that vectors don't subtype the way lists do,
> so (Vector Symbol Flonum) isn't an appropriate value when you need a
> (Vector Any (U Real False Interval)).  This isn't a problem when you
> don't have the keyword argument, because Typed Racket can figure out
> the needed types from the type of `discrete-histogram`, and so gives
> the vector literals appropriate types.  However, TR doesn't currently
> manage to propagate this information when looking at keyworded
> applications, which are much more complex when expanded.  Thus the
> behavior you're seeing.
> If we give TR a little help here, then this works:
> (define: lst : (Listof (Vector Any (U Real False Interval)))
>    (list #(A 1.0) #(B 2.0) #(B 3.0) (vector 'C (ivl 0.5 1.5))))
> (define (test2)
>    (plot (discrete-histogram lst #:label "Hello")))
> One way that `plot` could make this easier would be to support lists
> in addition to vectors for histogram data.

That wouldn't be hard to change. The contract and function are both 
defined in the file "plot/plot2d/rectangle.rkt". You want to take a 
crack at it, Ray? :)

You should only have to change the contract of `cat-vals' in 
`discrete-histogram' (to se `or/c'), and change the match pattern that 
destructures it to (list (or (vector cats ys) (list cats ys)) ...).

Neil ⊥

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