Improvre error-reporting

src/main/scala/com/github/kmizu/scomb/SCombinator.scala

@@ -454,7 +454,7 @@ abstract class SCombinator[R] {self =>
       val substring = current(index)
       literal.findPrefixOf(substring) match {
         case Some(prefix) => Success(prefix, index + prefix.length)
-        case None => Failure(s"expected:`${literal}`", index)
+        case None => Failure(s"expected:`${literal}` actual: `${current(index)(0)}`", index)
       }
     }
   }
@@ -477,7 +477,7 @@ abstract class SCombinator[R] {self =>
     } else if(current(index).startsWith(literal)) {
       Success(literal, index + literal.length)
     } else {
-      Failure(s"expected:`${literal}`", index)
+      Failure(s"expected:`${literal}` actual:`${current(index)(0)}`", index)
     }
   }
 

src/test/scala/com/github/kmizu/scomb/JsonSpec.scala

@@ -147,7 +147,7 @@ class JsonSpec extends FunSpec with DiagrammedAssertions {
     it("cannot parse incorrect array") {
       val failure = parse("[1, 2, ]").asInstanceOf[Result.Failure]
       assert(Location(1, 6) == failure.location)
-      assert("""expected:`]` in <rbracket>""" == failure.message)
+      assert("""expected:`]` actual:`,` in <rbracket>""" == failure.message)
     }
   }
 }

src/test/scala/com/github/kmizu/scomb/RegularExpressionSpec.scala

@@ -70,7 +70,7 @@ class RegularExpressionSpec extends FunSpec with DiagrammedAssertions {
       input = "(1|9)*"
       assert(parse(input) == Result.Success(Repeat(Choice(Value('1'), Value('9')))))
       input = "*"
-      assert(parse(input) == Result.Failure(Location(1, 1), "expected:`\\`"))
+      assert(parse(input) == Result.Failure(Location(1, 1), "expected:`\\` actual:`*`"))
     }
   }
 }