REPL throws an error when attempting to show a term

[jiribenes]

Problem

When I put an expression into the REPL, the REPL tries to call println($EXPR) which fails for all non-trivial types since #449:

> type TrafficLight { Red(); Yellow(); Green() }
> Red()
[error] Cannot typecheck call.
There are multiple overloads, which all fail to check:
[...]

Full error

Possible overload: option::println of type Option[Double] => Unit
  Argument count does not match TrafficLight2360 vs. Option593
  Expected type
    Option[Double]
  but got type
    TrafficLight

Possible overload: effekt::println of type String => Unit
  Expected String but got TrafficLight.

Possible overload: effekt::println of type Int => Unit
  Expected Int but got TrafficLight.

Possible overload: array::println of type Array[String] => Unit
  Argument count does not match TrafficLight2360 vs. Array1667
  Expected type
    Array[String]
  but got type
    TrafficLight

Possible overload: option::println of type Option[Bool] => Unit
  Argument count does not match TrafficLight2360 vs. Option593
  Expected Option[Bool] but got TrafficLight.

Possible overload: list::println of type List[Int] => Unit
  Argument count does not match TrafficLight2360 vs. List767
  Expected List[Int] but got TrafficLight.

Possible overload: option::println of type Option[Int] => Unit
  Argument count does not match TrafficLight2360 vs. Option593
  Expected Option[Int] but got TrafficLight.

Possible overload: list::println of type List[Double] => Unit
  Argument count does not match TrafficLight2360 vs. List767
  Expected List[Double] but got TrafficLight.

Possible overload: effekt::println of type Unit => Unit
  Expected Unit but got TrafficLight.

Possible overload: list::println of type List[String] => Unit
  Argument count does not match TrafficLight2360 vs. List767
  Expected List[String] but got TrafficLight.

Possible overload: array::println of type Array[Bool] => Unit
  Argument count does not match TrafficLight2360 vs. Array1667
  Expected Array[Bool] but got TrafficLight.

Possible overload: effekt::println of type Double => Unit
  Expected Double but got TrafficLight.

Possible overload: array::println of type Array[Double] => Unit
  Argument count does not match TrafficLight2360 vs. Array1667
  Expected type
    Array[Double]
  but got type
    TrafficLight

Possible overload: list::println of type List[Bool] => Unit
  Argument count does not match TrafficLight2360 vs. List767
  Expected List[Bool] but got TrafficLight.

Possible overload: effekt::println of type Ordering => Unit
  Expected Ordering but got TrafficLight.

Possible overload: effekt::println of type Bool => Unit
  Expected Bool but got TrafficLight.

Possible overload: array::println of type Array[Int] => Unit
  Argument count does not match TrafficLight2360 vs. Array1667
  Expected Array[Int] but got TrafficLight.

Source

Here's the code in question which just calls println on terms:

effekt/effekt/jvm/src/main/scala/effekt/Repl.scala

Lines 318 to 319 in aa897e4

	def makeEval(expr: Term): ModuleDecl =
	make(Call(IdTarget(IdRef(List(), "println")), Nil, List(expr), Nil))

Potential solution

If we don't want to wait for typeclasses #66, we could instead use inspect introduced in #449 because the REPL always runs with the JavaScript backend:
EDIT: Not true, the REPL runs with the backend of user's choice, see below. The workaround would only work for the JS and Chez backends

effekt/libraries/common/effekt.effekt

Lines 102 to 104 in aa897e4

	extern io def inspect[R](value: R): Unit =
	js { println(genericShow(value)) }
	chez { println(genericShow(value)) }

[marvinborner]

the REPL always runs with the JavaScript backend:

For debugging I often use different backends in the REPL, e.g. via effekt.sh --backend llvm
Am I misunderstanding this?

[jiribenes]

Thanks, I took a closer look and invalidated my assumption. The REPL runs for any backend...
I'll fix it in the original issue description.