lenses

[Tim Pigden]

Hi

I'm already using quite a lot of the generic features from shapeless.

Now I need lenses. But there are 2 different implementations in the typelevel stack - shapeless and monocle (not to mention scalaz).

Is anyone in a position to offer advice on the differences between them? In particular are there any strong reasons to favour monocle.

It should be noted I have a fairly large number of case classes in my data model and that some of them contain 20+ fields - I don't want to have to manually create lenses for all fields of all case classes if possible.

Tim

[Miles Sabin]

My take on this is that Monocle is the superior lens implementation
both in terms of generality and in terms of performance. shapeless has
a slight edge in terms of ease of use and boilerplate reduction.

I plan to do some more work on lenses for shapeless 3.0 which will
hopefully take them in an interesting direction and make them
competitive with Kmett-style lenses, but for now I would say that if
lenses are important to you you should use Monocle. OTOH if they're
incidental and you're already using shapeless then there's no
compelling reason not to use shapeless's.

I think Julien is on this list ... I think he'd probably agree with
the above ...

Cheers,


Miles

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[Tim Pigden]

Thanks

Been experimenting for the last hour or so with shapeless and it does look as if compilation speed is a problem. for example this

object Sites {

  object CustomerSiteLenses {
    val location = lens[CustomerSite].location
    //val timeWindows = lens[CustomerSite].timeWindows
    val siteType = lens[CustomerSite].siteType
    val fixedDuration = lens[CustomerSite].fixedDuration
    val loadRates = lens[CustomerSite].loadRates
    val unloadRates = lens[CustomerSite].unloadRates
    //val address = lens[CustomerSite].address
    val isArrivalConstraint = lens[CustomerSite].isArrivalConstraint
    val earlyFlexibility = lens[CustomerSite].earlyFlexibility
    val lateFlexibility = lens[CustomerSite].lateFlexibility
    val flexibleCost = lens[CustomerSite].flexibleCost
    //val siteFacilities = lens[CustomerSite].siteFacilities
    //val requiredVehicleFacilities = lens[CustomerSite].requiredVehicleFacilities
    //val allowedVehicleTypes = lens[CustomerSite].allowedVehicleTypes
    //val excludedVehicleTypes = lens[CustomerSite].excludedVehicleTypes

    //val _extension = lens[CustomerSite]._extension

  }

}

took some 77 seconds to compile. 

Will try monocle but keep my eye open for 3.0

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Tim Pigden
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[Miles Sabin]

On Fri, Jun 19, 2015 at 2:09 PM, Tim Pigden <tim.p...@optrak.com> wrote:
> Thanks
> Been experimenting for the last hour or so with shapeless and it does look
> as if compilation speed is a problem. for example this
>
> object Sites {
>
> object CustomerSiteLenses {
> val location = lens[CustomerSite].location
> //val timeWindows = lens[CustomerSite].timeWindows
> val siteType = lens[CustomerSite].siteType
> val fixedDuration = lens[CustomerSite].fixedDuration
> val loadRates = lens[CustomerSite].loadRates
> val unloadRates = lens[CustomerSite].unloadRates
> //val address = lens[CustomerSite].address
> val isArrivalConstraint = lens[CustomerSite].isArrivalConstraint
> val earlyFlexibility = lens[CustomerSite].earlyFlexibility
> val lateFlexibility = lens[CustomerSite].lateFlexibility
> val flexibleCost = lens[CustomerSite].flexibleCost
> //val siteFacilities = lens[CustomerSite].siteFacilities
> //val requiredVehicleFacilities =
> lens[CustomerSite].requiredVehicleFacilities
> //val allowedVehicleTypes = lens[CustomerSite].allowedVehicleTypes
> //val excludedVehicleTypes = lens[CustomerSite].excludedVehicleTypes
>
> //val _extension = lens[CustomerSite]._extension
>
> }
>
> }
>
> took some 77 seconds to compile.

What shapeless version? If coproducts are involved 2.2.2 should improve things.

[Tim Pigden]

Hi

It is 2.2.2 ( just went back and deleted all the older shapeless in my ivy cache to make sure)

Even if I reduce the above to the single uncommented value isArrivalConstraint - which is a boolean, it still takes about 6 seconds (newish i7)

Tim

[Miles Sabin]

On Fri, Jun 19, 2015 at 2:56 PM, Tim Pigden <tim.p...@optrak.com> wrote:
> It is 2.2.2 ( just went back and deleted all the older shapeless in my ivy
> cache to make sure)
> Even if I reduce the above to the single uncommented value
> isArrivalConstraint - which is a boolean, it still takes about 6 seconds
> (newish i7)

It'll be the number of fields in CustomerSite which is the issue ... how many?

If you can boil down something along the lines that Sam did for
Coproducts and post it here,

https://github.com/milessabin/shapeless/issues/381

that would be very helpful.

[杨博]

I would suggest https://github.com/adamw/quicklens, which seems easier than other implementations.

在 2015年6月19日星期五 UTC+8下午7:29:09，Tim Pigden写道：

[Matthew Pocock]

Sorry for resurrecting a zombie thread, but I sketched this out the other day:

https://github.com/drdozer/commandeer

It is a little macro that takes a trait and generates case classes for each operation. It would be fairly trivial to do essentially the same thing for the fields of a case class (generating a per-field command object that represents a query for that field), and then auto-generate the implicits from these case classes to the corresponding lens. While lenses don't have a single inhabitant, the case classes representing each field let you select exactly one.

Matthew

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