Re: [Chicken-users] R6RS immutable pair

[Kon Lovett]

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On Jul 12, 2006, at 2:42 PM, John Cowan wrote:

> Kon Lovett scripsit:
<snip>
> I'd like to see the existing pairs left alone, and new immutable pairs
> without identity added.  That is, (immutable-cons 1 2) is permitted  
> (but
> not required) to return the same pair (in the sense of EQ?) every time
> it's called.

Hash-Consing?

> All existing procedures would continue to work with immutable pairs
> except, of course, SET-CAR! and SET-CDR!.  Some decision would have to
> be taken about procedures like APPEND that accept multiple arguments:
> my initial take is that they should produce immutable results unless
> all the arguments are mutable.

You are suggesting contagion. I use this in the 'procedure-surface'  
composite for example.

> Scheme would need new procedures MUTABLE-PAIR?, IMMUTABLE-PAIR?,
> IMMUTABLE-CONS, IMMUTABLE-LIST, MUTABLE->IMMUTABLE, and
> IMMUTABLE->MUTABLE.

Mutable vs. Immutable should be a property of the object. Sorry, but  
I don't think we need *-immutable versions of every (<proc>  
<datatype> ...). Just a built-in flag and exception when a mutating  
operation attempted.

I think the R6RS editors are interested in Scheme source compiled. If  
it can be inferred that a datum is immutable then optimizations can  
be applied.

> --
> John Cowan   address@hidden    http://ccil.org/~cowan
> Original line from The Warrior's Apprentice by Lois McMaster Bujold:
> "Only on Barrayar would pulling a loaded needler start a stampede  
> toward one."
> English-to-Russian-to-English mangling thereof: "Only on Barrayar  
> you risk to
> lose support instead of finding it when you threat with the charged  
> weapon."

Yes, the "Miles" stories are a fun read.


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