Add bindFirst and curried methods for Poly

[Atry]

No description provided.

[codecov-io]

Codecov Report

Merging #708 into master will decrease coverage by 21.98%.
The diff coverage is 52.63%.

@@             Coverage Diff             @@
##           master     #708       +/-   ##
===========================================
- Coverage   83.58%   61.59%   -21.99%     
===========================================
  Files          66       94       +28     
  Lines        2608     3552      +944     
  Branches       90      114       +24     
===========================================
+ Hits         2180     2188        +8     
- Misses        428     1364      +936

Impacted Files	Coverage Δ
core/src/main/scala/shapeless/poly.scala	0% <0%> (-77.5%)	⬇️
core/src/test/scala/shapeless/poly.scala	81.25% <90.9%> (ø)
core/src/main/scala/shapeless/conversions.scala	0% <0%> (-100%)	⬇️
core/src/main/scala/shapeless/cached.scala	0% <0%> (-100%)	⬇️
core/src/main/scala/shapeless/unwrapped.scala	0% <0%> (-100%)	⬇️
core/src/main/scala_2.10/shapeless/lazyref.scala	0% <0%> (-100%)	⬇️
core/src/main/scala/shapeless/alacarte.scala	0% <0%> (-100%)	⬇️
...re/src/main/scala/shapeless/hlistconstraints.scala	0% <0%> (-100%)	⬇️
core/src/main/scala/shapeless/default.scala	0% <0%> (-100%)	⬇️
core/src/main/scala/shapeless/lowpriority.scala	0% <0%> (-100%)	⬇️
... and 48 more

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[Atry]

@milessabin Why did the code coverage change?

[milessabin]

This looks very useful ... thanks!

A few things before I merge. Do these work as expected as arguments to a Mapper? If not, then I suspect they would if the instances were moved to the corresponding CaseN companions. Either way, would you mind adding some tests of this case.

Also some stylistic things. shapeless intentionally doesn't use access modifiers (other than private[this] where it's interaction with variance can be useful). Also please could you adjust your use of whitespace to match the rest of the project (ie. two space indents with aggressive line breaking).

[Atry]

Yes, Mapper is my use case, too.

However, there is a limitation:

The newly created Poly from bindFirst or curried must be visible at the call site, which is impossible for some complicated case.

[milessabin]

Still waiting on tests and the stylistic changes requested.

[joroKr21]

Rebased to remove whitespace from diff and add some tests with map and foldLeft.
@milessabin regarding stylistic changes I think if we want a consistent style we should setup scalafmt.

[Atry]

Thank you for picking up this PR @joroKr21

[joroKr21]

@Atry do you remember what the ParameterAccumulator type parameter is for?
It seems unused to me = always HNil

[Atry]

    object p extends Poly3 {
      implicit def x = at[Int, Double, String] { (i, d, s) =>
        s"$i, $d, $s"
      }
    }

    val c = Poly.curried(p)
    val c1 = c(1)
    val c2 = c1(42.5)

Try printing c2.

[joroKr21]

Ah ok that makes sense 👍