On 04/29/2012 04:33 PM, Matthias Felleisen wrote:
On Apr 29, 2012, at 6:29 PM, Asumu Takikawa wrote:
On 2012-04-29 12:43:48 -0400, Matthias Felleisen wrote:
What you're really saying is that sequence-map uses the wrong kind of type.
Specifically, it should be polymorphic in the sequence constructor instead of
mapping everything to the top of the class hierarchy (sequence).
I don't think this is just a type issue. The sequence that is returned
by `sequence-map` is lazy, even if the original sequence was not. That's
why you can't get the original type.
Cheers,
Asumu
Why is it lazy?
Can we add a strict one that is polymorphic (I apologize to the
defenders of proper type terminology here for the applying this word
to a dynamic aspect of Racket programs) in the sequence type-tag?
Another problem is that not all sequence types are polymorphic. For
example, strings are sequences, but strings can contain only characters.
So what would
(sequence-map char->integer "abc")
return? Custom sequence types can add arbitrary additional constraints.
Ryan
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