[Haskell-cafe] A first glimps on the {-# NOUPDATE #-} pragma

[Joachim Breitner]

Hi Facundo,

Am Mittwoch, den 29.08.2012, 10:26 -0300 schrieb Facundo Domínguez:
> >         upd_noupd n =
> >             let l = myenum' 0 n
> >             in last l + length l
> 
> This could be rewritten as
> 
> >         upd_noupd n =
> >             let l n = myenum' 0 n
> >             in last (l n) + length (l n)
> 
> Or a special form of let could be introduced to define locally-scoped macros:
> 
> >         upd_noupd n =
> >             let# l = myenum' 0 n
> >             in last l + length l
> 
> What's the strength of the {-# NOUPDATE #-} approach?

it does not require refactoring of the code. There is not always a
parameter handy that you can use to prevent sharing, and using () for
that sometimes fails due to the full-lazyness-transformation.

And a locally-scoped macros would not help in this case:

        test g n = g (myenum' 0 n)

Now you still might want to prevent the long list to be stored, but here
it cannot be done just by inlining or macro expansion.


Greetings,
Joachim

-- 
Dipl.-Math. Dipl.-Inform. Joachim Breitner
Wissenschaftlicher Mitarbeiter
http://pp.info.uni-karlsruhe.de/~breitner
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