[plt-scheme] hash-has-key?

From: Robby Findler (robby at eecs.northwestern.edu)
Date: Sat Mar 28 09:33:13 EDT 2009

There seems to be compounding confusion here ....

On Sat, Mar 28, 2009 at 8:26 AM, Matthias Felleisen
<matthias at ccs.neu.edu> wrote:
>
> On Mar 28, 2009, at 8:41 AM, Dave Herman wrote:
>
>> Because Scheme is untyped, it's not possible for hash-ref to return one
>> standard "not found" value, so the API ought to provide a predicate.

I'm not sure what this means. hash-ref accepts a thunk to call in the
case the result isn't found.

(I agree with the earlier conclusions that a built-in hash-bound?
predicate is desirable, tho.)

> Because Typed Scheme is typed, it's not possible for hash-ref to use one
> standard "not found" type, so the API ought to provide the return
> type.

hash-ref does not return a standard not found type.
Robby


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