[racket] Some questions regarding exercises in PLAI

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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>>>  http://lists.racket-lang.org/listinfo/users
>>
>>
>>
>> --
>> 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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