Return-Path: <kfoury@cs.bu.edu> X-Spam-HitLevel: X-Spam-DCC: INFN-TO: cs3.bu.edu 1233; Body=1 Fuz1=1 Fuz2=1 X-Spam-Checker-Version: SpamAssassin 3.1.0 (2005-09-13) on cs3.bu.edu X-Spam-Level: X-Spam-Status: No, score=-4.4 required=10.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.1.0 X-Spam-Pyzor: Received: from [76.19.13.75] ([76.19.13.75]) (authenticated bits=0) by cs3.bu.edu (8.13.6/8.13.6) with ESMTP id k9O4MFGm004750; Tue, 24 Oct 2006 00:22:25 -0400 Message-ID: <453D9508.1070409@cs.bu.edu> Date: Tue, 24 Oct 2006 00:22:32 -0400 From: Assaf Kfoury <kfoury@cs.bu.edu> User-Agent: Mozilla Thunderbird 1.0.7 (X11/20051013) X-Accept-Language: en-us, en To: Michel Machado <michel@digirati.com.br> CC: cs520@cs.bu.edu Subject: Re: Evaluation Context - Derivation References: <00e301c6f632$b1451490$16b6a8c0@dark> <453C4618.2010202@cs.bu.edu> <003b01c6f6a6$cd744130$24b6a8c0@dark> In-Reply-To: <003b01c6f6a6$cd744130$24b6a8c0@dark> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Clamav-Status: No Status: RO Content-Length: 2426 X-UID: 29 X-Keywords:
Wait until the lecture on Tuesday morning. Hopefully some of the issues
you raise will be clarified.
Assaf
Michel Machado wrote:
> Hi Assaf,
>
> Since E is just [ ], the output of plug is t. So, I have to use the
> previous rules to evaluate t to a value.
>
> I've thought Evaluation Context were an alternative to the rules
> we've been working so far. If not, what is Evaluation Context intended
> to? Could you show an application of it?
>
> [ ]'s
> Michel Machado
>
> ----- Original Message ----- From: "Assaf Kfoury" <kfoury@cs.bu.edu>
> To: "Michel Machado" <michel@digirati.com.br>
> Cc: <cs520@cs.bu.edu>
> Sent: Monday, October 23, 2006 12:33 AM
> Subject: Re: Evaluation Context - Derivation
>
>
>> Let t be the term "(lam x. x + 2) 3". The whole of t is a beta-redex.
>> So, the corresponding evaluation context E for t is simply [ ],
>> consisting of a hole and nothing else. (I write E instead of E_cbv or
>> E_cbn, for brevity.)
>>
>> Here plug(t,[ ]) = t. The whole of t is a beta-redex such that t ->
>> (3 + 2).
>>
>> I said in lecture that the approach to evaluation (or operational
>> semantics) based on evaluation contexts is "more scalable". What I
>> meant is that if we extend the language by adding new programming
>> features, then the operational semantics based on evaluation contexts
>> "more easily scales up" to the extended language. This is not a
>> theorem and there is no proof for it -- it is just an observation
>> based on experience (mine and that of many other researchers in this
>> area), but for which I did not give any examples in lecture.
>>
>> Scalability, i.e. the ability to extend a property from a smaller
>> language to a larger language, has nothing to do with efficiency or
>> "faster evaluation".
>>
>> Assaf
>>
>> Michel Machado wrote:
>>
>>> Hi Assaf,
>>>
>>> Could you write the derivation of the term (lam x. x + 2) 3 using
>>> evaluation contexts?
>>>
>>> I don't see what the first Ecvb in plug function should be. I
>>> mean, how can I complete the following expression in order to eval
>>> that term?
>>>
>>> plug(t, Ecbv) = plug((lam x. x + 2) 3, ????) = ????
>>>
>>> Do you have other links about evaluation contexts?
>>>
>>> You said in last class that evaluation contexts are more
>>> scalable, in what sense is it more scalable? Does it lead to faster
>>> evaluation?
>>>
>>> [ ]'s
>>> Michel Machado
>>
>>
>>
>>
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