I think I've run into this problem before. The type of array-slice-ref is
(Array A) (Listof Slice-Spec) -> (Array A)
where Slice-Spec = (U (Sequenceof Integer) Integer ....)
The problem is that integers are also sequences, so the contract
generated for Slice-Spec just discards the Integer part. (I can't
remember if it's done by type->contract or by or/c.) Then when given an
integer, the sequenceof contract accepts it and produces a sequence
proxy that is not an integer.
Basically, 0 gets turned into (in-range 0), which is an empty sequence.
I don't know of a workaround that uses only untyped code, but you can
define a typed alternative version of array-slice-ref that accepts a
version of Slice-Spec with the (Sequenceof Integer) removed (or replaced
with lists and/or vectors). Then if you use that in untyped code, it
should work as expected because the overlap is gone.
Ryan
On 10/21/2015 12:30 PM, Berthold Bäuml wrote:
When using array-slice-ref from math/array I get different results
when executing it #lang typed/racket or #lang racket (see below). The
typed/racket result is consistent with the documentation, the untyped
one seems to be wrong.
Berthold
#lang typed/racket
(require math/array)
(define arr
(array
#[#[#["000" "001" "002" "003"]
#["010" "011" "012" "013"]
#["020" "021" "022" "023"]]
#[#["100" "101" "102" "103"]
#["110" "111" "112" "113"]
#["120" "121" "122" "123"]]]))
(array-slice-ref arr (list 0 ::…))
computes to:
(array #[#["000" "001" "002" "003"] #["010" "011" "012" "013"] #["020" "021" "022"
"023"]])
wheras:
#lang racket
(require math/array)
(define arr
(array
#[#[#["000" "001" "002" "003"]
#["010" "011" "012" "013"]
#["020" "021" "022" "023"]]
#[#["100" "101" "102" "103"]
#["110" "111" "112" "113"]
#["120" "121" "122" "123"]]]))
(array-slice-ref arr (list 0 ::…))
computes to:
(array #[])
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