suspensions

[Luke_H]

I've been working through the book "Purely functional data structures" using SML/NJ and came to the $ notation for creating suspensions.  It seems as though SML/NJ has some kind of $-based notation, but it doesn't behave the same way as the one in the book.  For instance, $f x doesn't work - it seems to bind as ($f) x - and writing $(f x) isn't what you want because that evaluates "f x" eagerly.  The samples in the book don't compile and I can't find any mention of the $ notation in the documentation or indeed anywhere online.

Can anyone explain how the $ stuff works in SML/NJ?  Any help would be much appreciated :)

[John Reppy]

I believe that what is supported in SML/NJ is based on Wadler et al's  
design
as described in

        How to Add Laziness to a Strict Language Without Even Being Odd,
        Workshop on ML, 1998.

Here is a link to the paper

        http://homepages.inf.ed.ac.uk/wadler/papers/lazyinstrict/lazyinstrict.ps

Hope this helps.

        - John

On Jan 18, 2008, at 2:37 PM, Luke_H wrote:

>
> I've been working through the book "Purely functional data  
> structures" using
> SML/NJ and came to the $ notation for creating suspensions.  It  
> seems as
> though SML/NJ has some kind of $-based notation, but it doesn't  
> behave the
> same way as the one in the book.  For instance, $f x doesn't work -  
> it seems
> to bind as ($f) x - and writing $(f x) isn't what you want because  
> that
> evaluates "f x" eagerly.  The samples in the book don't compile and  
> I can't
> find any mention of the $ notation in the documentation or indeed  
> anywhere
> online.
>
> Can anyone explain how the $ stuff works in SML/NJ?  Any help would  
> be much
> appreciated :)
> --
> View this message in context: http://www.nabble.com/suspensions-tp14957803p14957803.html
> Sent from the SML/NJ mailing list archive at Nabble.com.
>
>
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[Luke_H]

Thanks John - the paper is indeed useful reading.  Unfortunately I'm
still having problems using the $ notation in SML/NJ as described in
that paper - for example, take the 'map' function from near the end (fig
7 in fact)

fun $map f ($Nil) = $Nil
...

This gives an error "non-constructor applied to argument in pattern"

I've used the "Control.lazysml := true" directive.  Is there anything
else that needs to be done to get this syntax to work?  Or has this
functionality not been implemented in the compiler as described in the
paper?

Many thanks :)

- Luke

-----Original Message-----
From: John Reppy [mailto:jhr@...]
Sent: 18 January 2008 21:38
To: Luke Halliwell
Cc: smlnj-list@...
Subject: Re: [Smlnj-list] suspensions

I believe that what is supported in SML/NJ is based on Wadler et al's  
design
as described in

        How to Add Laziness to a Strict Language Without Even Being Odd,
        Workshop on ML, 1998.

Here is a link to the paper

       
http://homepages.inf.ed.ac.uk/wadler/papers/lazyinstrict/lazyinstrict.ps

Hope this helps.

        - John

On Jan 18, 2008, at 2:37 PM, Luke_H wrote:

>
> I've been working through the book "Purely functional data  
> structures" using
> SML/NJ and came to the $ notation for creating suspensions.  It  
> seems as
> though SML/NJ has some kind of $-based notation, but it doesn't  
> behave the
> same way as the one in the book.  For instance, $f x doesn't work -  
> it seems
> to bind as ($f) x - and writing $(f x) isn't what you want because  
> that
> evaluates "f x" eagerly.  The samples in the book don't compile and  
> I can't
> find any mention of the $ notation in the documentation or indeed  
> anywhere
> online.
>
> Can anyone explain how the $ stuff works in SML/NJ?  Any help would  
> be much
> appreciated :)
> --
> View this message in context:

http://www.nabble.com/suspensions-tp14957803p14957803.html
> Sent from the SML/NJ mailing list archive at Nabble.com.
>
>
>
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-
> This SF.net email is sponsored by: Microsoft
> Defy all challenges. Microsoft(R) Visual Studio 2008.
> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
> _______________________________________________
> Smlnj-list mailing list
> Smlnj-list@...
> https://lists.sourceforge.net/lists/listinfo/smlnj-list
>


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