[Haskell-cafe] Record update fusion (or how should I call it?)

Derek Elkins derek.a.elkins at gmail.com
Sun Sep 6 15:04:08 EDT 2009

The first thing I would do i is verify that the compiler is not
already doing this.

On Sun, Sep 6, 2009 at 7:50 AM, Peter Verswyvelen<bugfact at gmail.com> wrote:
> I've seen a couple of package being announced that provide first class
> labels, and other packages already existed for this (Grapefruit
> Record, HList, Accessor, ...)
> Regarding this, I have a question about the performance of multiple
> composed field updates. Maybe an example.
> Suppose I have a large record - say WindowDescription - which contains
> a lot of fields.
> Suppose I have a couple of default window description values, e.g.
> defaultWindowDesc, dialogBoxDesc, etc
> Using accessors it is easy to take such a default value, and "modify"
> a couple of fields, like:
> let myWindowDesc = set title "Haskell" . set size (640,480) . set
> background Blue . set fontFamily Arial $ defaultWindowDesc
> However, I guess this would make a lot of intermediate
> WindowDescription copies no (whether the fields are strict or not)? So
> ideally for performance, all these "updates" should be fused, maybe
> running inside an ST monad?
> I'm not sure if any of this is valid, but I would like to understand
> more about this, so any links and hints are welcome :-)
> Peter Verswyvelen
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