user defined implicits interfere with ammonites internal implicits

[cvogt]

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Welcome to the Ammonite Repl 0.4.6
(Scala 2.11.7 Java 1.8.0_45)
@ trait Lower {implicit def monad[M[_],T](i: T): M[T] = ???; implicit def preventNothing[T](i: T): Nothing = ??? }
^[[A^[[A^[[Adefined trait Lower
@ object Higher extends Lower{ implicit def value[M[_],T](l: M[T]): T = ??? }
defined object Higher
@ import Higher._
import Higher._
@ List(1,2,3) * List(2,3,4)
scala.NotImplementedError: an implementation is missing
    scala.Predef$.$qmark$qmark$qmark(Predef.scala:225)
    cmd1$Higher$.value(Main.scala:38)
    cmd3$$anonfun$1.apply$mcI$sp(Main.scala:57)
    cmd3$.<init>(Main.scala:58)
    cmd3$.<clinit>(Main.scala:-1)

@ def foo[M[_],T](l: M[T]) = l
defined function foo
@ import scala.util.Try
import scala.util.Try
@ Try(foo(List(1,2,3) * List(2,3,4)))
Compilation Failed
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method preventNothing in trait Lower of type [T](i: T)Nothing
 and method monad in trait Lower of type [M[_], T](i: T)M[T]
 are possible conversion functions from Unit to pprint.PPrint[Any]
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method preventNothing in trait Lower of type [T](i: T)Nothing
 and method monad in trait Lower of type [M[_], T](i: T)M[T]
 are possible conversion functions from Unit to pprint.PPrint[Any]
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method monad in trait Lower of type [M[_], T](i: T)M[T]
 and method preventNothing in trait Lower of type [T](i: T)Nothing
 are possible conversion functions from Unit to pprint.PPrint[Any]
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method monad in trait Lower of type [M[_], T](i: T)M[T]
 and method preventNothing in trait Lower of type [T](i: T)Nothing
 are possible conversion functions from Unit to pprint.PPrint[Any]
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method monad in trait Lower of type [M[_], T](i: T)M[T]
 and method preventNothing in trait Lower of type [T](i: T)Nothing
 are possible conversion functions from Unit to pprint.PPrint[Any]

[lihaoyi]

Here's a better repro

@ trait Lower {implicit def monad[M[_],T](i: T): M[T] = ???; implicit def preventNothing[T](i: T): No  thing = ??? }
defined trait Lower
@ object Higher extends Lower{ implicit def value[M[_],T](l: M[T]): T = ??? }
defined object Higher
@ ??? : Any
scala.NotImplementedError: an implementation is missing
    scala.Predef$.$qmark$qmark$qmark(Predef.scala:225)
    cmd3$.<init>(Main.scala:47)
    cmd3$.<clinit>(Main.scala:-1)

@  import Higher._
import Higher._
@ ??? :  @Any
Compilation Failed
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method preventNothing in trait Lower of type [T](i: T)Nothing
 and method monad in trait Lower of type [M[_], T](i: T)M[T]
 are possible conversion functions from Unit to pprint.PPrint[Any]
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method preventNothing in trait Lower of type [T](i: T)Nothing
 and method monad in trait Lower of type [M[_], T](i: T)M[T]
 are possible conversion functions from Unit to pprint.PPrint[Any]
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method monad in trait Lower of type [M[_], T](i: T)M[T]
 and method preventNothing in trait Lower of type [T](i: T)Nothing
 are possible conversion functions from Unit to pprint.PPrint[Any]
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method monad in trait Lower of type [M[_], T](i: T)M[T]
 and method preventNothing in trait Lower of type [T](i: T)Nothing
 are possible conversion functions from Unit to pprint.PPrint[Any]
type mismatch;
 found   : Unit
 required: pprint.PPrint[Any]
Note that implicit conversions are not applicable because they are ambiguous:
 both method monad in trait Lower of type [M[_], T](i: T)M[T]
 and method preventNothing in trait Lower of type [T](i: T)Nothing
 are possible conversion functions from Unit to pprint.PPrint[Any]

[lihaoyi]

Still fails on the 0.9.0, but with a different error

@
trait Lower {implicit def monad[M[_],T](i: T): M[T] = ???; implicit def preventNothing[T](i: T): Nothing = ??? }
defined trait Lower
@  object Higher extends Lower{ implicit def value[M[_],T](l: M[T]): T = ??? }
defined object Higher
@ ??? : Any
scala.NotImplementedError: an implementation is missing
  scala.Predef$.$qmark$qmark$qmark(Predef.scala:284)
  $sess.cmd2$.<init>(cmd2.sc:1)
  $sess.cmd2$.<clinit>(cmd2.sc:-1)

@ import Higher._
import Higher._
@ ??? : Any
cmd4.sc:8: type mismatch;
 found   : String("Any")
 required: fansi.Str
Note that implicit conversions are not applicable because they are ambiguous:
 both method preventNothing in trait Lower of type [T](i: T)Nothing
 and method monad in trait Lower of type [M[_], T](i: T)M[T]
 are possible conversion functions from String("Any") to fansi.Str
            .print(res4, "res4", _root_.scala.None)
                  ^
Compilation Failed
@

[lihaoyi]

A self-contained example

@ {{
  trait Lower {
    implicit def monad[M[_],T](i: T): M[T] = ???
    implicit def preventNothing[T](i: T): Nothing = ???
  }
  object Higher extends Lower{
    implicit def value[M[_],T](l: M[T]): T = ???
  }
  import Higher._

  def print[T: pprint.TPrint](value: => T) = ???
  print(1)
  }}
cmd2.sc:12: type mismatch;
 found   : String("Int")
 required: fansi.Str
Note that implicit conversions are not applicable because they are ambiguous:
 both method monad in trait Lower of type [M[_], T](i: T)M[T]
 and method preventNothing in trait Lower of type [T](i: T)Nothing
 are possible conversion functions from String("Int") to fansi.Str
print(1)
     ^
Compilation Failed

Seems the pprint.TPrint implicit is misbehaving