I am not sure it is a good idea to add many almost-synonyms in a language. I just was a little bit curious. The change is backward compatible and I have no objections against it. Indeed values to be inserted for missing keys often are #f or 0 or '( ). It types nicely not having to wrap these basic constants in a thunk and to gain efficiency for free. You only have to be aware of the fact that if the value to be inserted is to be or might be a procedure, such as (lambda (x) x) as the most elementary procedure when building a hash of procedures, you have to wrap it as (lambda ( ) (lambda (x) x)). Because the latter does not capture any variables, it may even be optimized such as to avoid multiple construction of the identity function. In this case I would write or have my macro or module expand to for example: (define (identity x) x) (define (default) identity) (let loop ((...)) ... (hash-ref! hash key default) ...) I am pretty sure that in this case the identity function is constructed once only. Jos
_____ From: Neil Van Dyke [mailto:n...@neilvandyke.org] Sent: 19 July 2010 00:22 To: Jos Koot Cc: 'plt-scheme' Subject: Re: [racket] hash-ref Jos Koot wrote at 07/18/2010 09:26 AM: (hash-ref a-hash a-key a-value) In the past a-value was required to be a procedure. Now it can be anything. [...] In short, I do not well understand the reason to relax the contract of hash-ref and hash-ref!. This behavior seems a little on the uncomfortable side of automagical to me, and -- although I can understand the desire to keep the short name -- I would've preferred separate procedures for the default-thunk and default-value variations. Perhaps the short-name procedure could be the automagical one, and there could be longer-name procedures, like "hash-ref/default-thunk" and "hash-ref/default-value", for people who prefer a little less automagic in that regard. -- http://www.neilvandyke.org/
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