[racket] Some questions regarding exercises in PLAI

Thanks for your replies. It's all clear now.

And thanks for the book! :)

On 01/Sep/10 5:49 AM, Shriram Krishnamurthi wrote:
> Sorry for the delay.  In this case, Eric's interpretation is the one I
> had in mind!
>
> On Mon, Aug 30, 2010 at 9:40 AM, Eric Tanter<etanter at dcc.uchile.cl>  wrote:
>> Hi Ionut, Jay,
>>
>> I don't understand the question this way -- rather, how to maintain laziness without introducing an extra variant of CFAE-Value, ie. reusing the Closure variant to implement expression closures.
>>
>> Maybe Shriram can confirm which interpretation is correct ;)
>>
>> -- Éric
>>
>>
>> On Aug 30, 2010, at 9:21 AM, Jay McCarthy wrote:
>>
>>> Hi Ionut,
>>>
>>> In this section PLAI is asking you to write more of a meta-interpreter
>>> where you use the thunks of the language you are writing the
>>> interpreter in.
>>>
>>> Jay
>>>
>>> On Mon, Aug 30, 2010 at 2:23 AM, Ionut G. Stan<ionut.g.stan at gmail.com>  wrote:
>>>> Hi,
>>>>
>>>> I'm pretty sure this is not the best mailing list to ask about PLAI, but as
>>>> I've found no other I decided to try here (I've found about PLAI on the
>>>> original DrScheme mailing list, and racket-lang.org seems to mention PLAI in
>>>> the "Learning" section). I won't mind if I don't get an answer to my
>>>> question though. Maybe there's a dedicated mailing list?
>>>>
>>>> So, here's my problem, just in case :)
>>>>
>>>> I'm stuck understanding what a certain exercise is asking me. I'm talking
>>>> about exercise 8.2.1 from chapter 8, Implementing Laziness.
>>>>
>>>> The exercise asks to implement laziness without using expression closures,
>>>> but using thunks instead. Thunks being just like closure, except they don't
>>>> have arguments bound to them. What I don't understand is the fact that this
>>>> is the way I've implemented expression closures. They're just like closures,
>>>> except for the argument part. So, from my point of view, is just a matter of
>>>> renaming my algebraic data types.
>>>>
>>>> I'm using Haskell to implement all the languages discussed in the book, and
>>>> my ADT for CFAE/L-Value looks like this:
>>>>
>>>> data CFAELValue
>>>>     = NumberValue Int
>>>>     | Closure String CFAEL Environment
>>>>     | Expression CFAEL Environment
>>>>     deriving (Eq, Show)
>>>>
>>>> So, Expression is the constructor for expression closures, and the only
>>>> difference when compared to Closure is the String argument.
>>>>
>>>> Is anyone willing to shed some light on what the exercise does actually
>>>> require me to do?
>>>>
>>>> Just for completeness, I've put the Haskell sources for all the languages up
>>>> to chapter 8 on Github: http://github.com/igstan/plai-haskell. CFAE-L.hs is
>>>> the one used for chapter 8.
>>>>
>>>> Thanks.
>>>>
>>>> --
>>>> Ionuț G. Stan  |  http://igstan.ro
>>>> _________________________________________________
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>>>
>>>
>>>
>>> --
>>> Jay McCarthy<jay at cs.byu.edu>
>>> Assistant Professor / Brigham Young University
>>> http://teammccarthy.org/jay
>>>
>>> "The glory of God is Intelligence" - D&C 93
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>>
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-- 
Ionuț G. Stan  |  http://igstan.ro