milessabin/shapeless — pull request #9 by sirthias (2012-07-18 14:19:34+00:00)
Title: Improve HList Prepend with special handling for HNil

I came across a use case in my application that required an implicit `Prepend` where it shouldn't be needed. Since I'm trying to limit implicit parameters to only the cases where they are really necessary (they complicate the design of my DSL) I propose this small patch.

Essentially my patch makes the following two methods compile, where the compiler currently requires an implicit `Prepend` parameter.

```scala
def prependWithHNil[L <: HList](list: L) = HNil ::: list
def prependToHNil[L <: HList](list: L) = list ::: HNil
```