Implementation of lazy_t

Implementation of lazy_t

[Florian Lorenzen]

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Hello,

I would like to know how lazy datatype constructors are implemented in
OCaml. A look into the documentation of the Lazy module revealed that
the compiler uses a built-in type constructor lazy_t for this
purpose. Unfortunately, I could not find any information on lazy_t on
the web. My question is how lazy datatypes are handled internally
(without having to read the compiler's source code). Especially, if
lazy_t implements call-by-need in the sense that once evaluated
objects are not evaluated again (by means of sharing) or if it
implements call-by-name like one can do by inserting 0-ary lambda
abstractions in the constructor to suspend evaluation and applying
them to force evaluation?

Is there any documentation on the internals available or can someone
shine some light on this?

Thanks a lot and best regards,

Florian


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Re: [Caml-list] Implementation of lazy_t

[David Teller]

On Mon, 2008-11-10 at 17:31 +0100, Florian Lorenzen wrote:
> Especially, if
> lazy_t implements call-by-need in the sense that once evaluated
> objects are not evaluated again (by means of sharing) or if it
> implements call-by-name like one can do by inserting 0-ary lambda
> abstractions in the constructor to suspend evaluation and applying
> them to force evaluation?

That's call-by-need indeed. 

Cheers,
 David
-- 
David Teller-Rajchenbach
 Security of Distributed Systems
  http://www.univ-orleans.fr/lifo/Members/David.Teller
 Angry researcher: French Universities need reforms, but the LRU act brings liquidations. 

Re: [Caml-list] Implementation of lazy_t

[Mauricio Fernandez]

On Mon, Nov 10, 2008 at 05:31:15PM +0100, Florian Lorenzen wrote:
> Hello,
> 
> I would like to know how lazy datatype constructors are implemented in
> OCaml. A look into the documentation of the Lazy module revealed that
> the compiler uses a built-in type constructor lazy_t for this
> purpose. Unfortunately, I could not find any information on lazy_t on
> the web. My question is how lazy datatypes are handled internally
> (without having to read the compiler's source code). Especially, if
> lazy_t implements call-by-need in the sense that once evaluated
> objects are not evaluated again (by means of sharing) or if it
> implements call-by-name like one can do by inserting 0-ary lambda
> abstractions in the constructor to suspend evaluation and applying
> them to force evaluation?
> 
> Is there any documentation on the internals available or can someone
> shine some light on this?

See stdlib/camlinternalLazy.ml --- force takes but 6 lines of code.

-- 
Mauricio Fernandez  -   http://eigenclass.org

Re: [Caml-list] Implementation of lazy_t

[Andrej Bauer]

If I may advertise myself, have a look at the implementation of
MiniHaskell at the PL Zoo, http://andrej.com/plzoo/ . It has lazy
lists, and the code is supposed to be educational.

Hmm, looking at interp.ml I see that it's not as call-by-need as it
could be. So, a good exercise then is to fix the interpreter to make
it lazier :-)

Best regards,

Andrej

> On Mon, Nov 10, 2008 at 05:31:15PM +0100, Florian Lorenzen wrote:
>> I would like to know how lazy datatype constructors are implemented in
>> OCaml.

Re: [Caml-list] Implementation of lazy_t

[Florian Lorenzen]

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Mauricio Fernandez wrote:
> On Mon, Nov 10, 2008 at 05:31:15PM +0100, Florian Lorenzen wrote:
> See stdlib/camlinternalLazy.ml --- force takes but 6 lines of code.
Thank you Mauricio. That pointer helped.

Regards,

Florian


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