Unknown externs cause unnecessary errors
def a: Int = extern("native:foo")
def b: Int = extern("native:bar")
def x = a + b
out x
causes an error (Error: <unknown location>: Internal error: java.lang.ClassCastException: class de.uni_luebeck.isp.tessla.core.ConstantEvaluator$$$Lambda$362/0x0000000100340840 cannot be cast to class scala.math.BigInt
) but
def a: Int = extern("native:foo")
out a
works. According to the LanSpec such a definition and usage of externs should be possible.