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a partially applied function and a type class
Sat, 2010-07-31, 21:14
hi, i was just reading up on type classes and wanted to give it a try.
so i wrote an example type class
abstract class LogFormatter[A] { def format(a: A): String }
object LogFormatter { implicit object StringLogFormatter extends LogFormatter[String] { def format(s: String) = ... } implicit object ExceptionLogFormatter extends LogFormatter[Exception] { def format(e: Exception) = ... }}
i wanted to use this like so
object Logger { def log[A: LogFormatter](level: Int)(a: A) { val formatted = implicitly[LogFormatter[A]].format(a) ... }}
and then do
val x = Logger.log(0) _x("s") x(new RuntimeException)
but it seems i am unable to, because with the partially applied function, the implicit LogFormatter type is Nothing and i don't want to define this in my LogFormatter object.
any suggestions for how this might be accomplished, or for a better approach, are most welcome.
thanks! -Eric
so i wrote an example type class
abstract class LogFormatter[A] { def format(a: A): String }
object LogFormatter { implicit object StringLogFormatter extends LogFormatter[String] { def format(s: String) = ... } implicit object ExceptionLogFormatter extends LogFormatter[Exception] { def format(e: Exception) = ... }}
i wanted to use this like so
object Logger { def log[A: LogFormatter](level: Int)(a: A) { val formatted = implicitly[LogFormatter[A]].format(a) ... }}
and then do
val x = Logger.log(0) _x("s") x(new RuntimeException)
but it seems i am unable to, because with the partially applied function, the implicit LogFormatter type is Nothing and i don't want to define this in my LogFormatter object.
any suggestions for how this might be accomplished, or for a better approach, are most welcome.
thanks! -Eric
Sat, 2010-07-31, 21:57
#2
Re: a partially applied function and a type class
Would it make sense to allow currying to delay type parameters, or to allow curried type parameters without explicitly encoding it like jason's example?
On Jul 31, 2010 4:27 PM, "Jason Zaugg" <jzaugg@gmail.com> wrote:
http://gist.github.com/502572
-jason
On Sat, Jul 31, 2010 at 10:14 PM, Eric Thul <eric.thul@gmail.com> wrote:
> hi, i was just reading u...> any suggestions for how this might be accomplished, or for a better
> approach, are most welcome.
Sat, 2010-07-31, 22:27
#3
Re: a partially applied function and a type class
thanks for the replies, this is perfect!
On Sat, Jul 31, 2010 at 4:55 PM, Josh Suereth <joshua.suereth@gmail.com> wrote:
On Sat, Jul 31, 2010 at 4:55 PM, Josh Suereth <joshua.suereth@gmail.com> wrote:
Would it make sense to allow currying to delay type parameters, or to allow curried type parameters without explicitly encoding it like jason's example?
On Jul 31, 2010 4:27 PM, "Jason Zaugg" <jzaugg@gmail.com> wrote:
http://gist.github.com/502572
-jason
On Sat, Jul 31, 2010 at 10:14 PM, Eric Thul <eric.thul@gmail.com> wrote:
> hi, i was just reading u...> any suggestions for how this might be accomplished, or for a better
> approach, are most welcome.
Sat, 2010-07-31, 23:07
#4
Re: a partially applied function and a type class
Partial application of method type parameters implies that
FunctionN#apply must be type parametric (to accept the remaining type
params.) In addition, any view or context bounds of these type params
would need map to extra implicit parameters of this apply method. Not
entirely straightforward...
Runar's recent post, "Higher Rank Polymorphism in Scala" [1] shows how
to encode one specific case of this sort of thing.
The toolbox for abstraction in this area is far from complete!
-jason
[1] http://apocalisp.wordpress.com/2010/07/02/higher-rank-polymorphism-in-sc...
On Sat, Jul 31, 2010 at 10:55 PM, Josh Suereth wrote:
> Would it make sense to allow currying to delay type parameters, or to allow
> curried type parameters without explicitly encoding it like jason's example?
>
> On Jul 31, 2010 4:27 PM, "Jason Zaugg" wrote:
>
> http://gist.github.com/502572
>
>> any suggestions for how this might be accomplished, or for a better
>> approach, are most welcome.
http://gist.github.com/502572
-jason
On Sat, Jul 31, 2010 at 10:14 PM, Eric Thul wrote:
> hi, i was just reading up on type classes and wanted to give it a try.
> so i wrote an example type class
>
> any suggestions for how this might be accomplished, or for a better
> approach, are most welcome.