Brought lexer up to date

lexer/test-common.go

@@ -30,11 +30,11 @@ func testStringErr (
 	correct     ...Token,
 ) {
 	testError := func (err error) bool {
-		got := err.(*errors.Error)
-		gotMessage := got.Message
-		gotLine    := got.Line
-		gotRow     := got.Position.Row
-		gotStart   := got.Position.Start
+		got := err.(errors.Error)
+		gotMessage := got.Error()
+		gotLine    := got.Position().Line
+		gotRow     := got.Position().Row
+		gotStart   := got.Position().Start
 		correct :=
 			gotMessage == errMessage &&
 			gotLine    == errLine    &&
@@ -42,28 +42,24 @@ func testStringErr (
 			gotStart   == errStart
 		if !correct {
 			test.Log("errors do not match")
-			test.Log("got:\n"     + got.Format())
-			test.Log("correct:\n" + (&errors.Error {
-				Position: errors.Position {
+			test.Log("got:\n"     + errors.Format(got))
+			test.Log("correct:\n" + errors.Format(errors.Errorf (
+				errors.Position {
 					File:  "input.fspl",
 					Line:  errLine,
 					Row:   errRow,
 					Start: errStart,
 					End:   errStart,
 				},
-				Message: errMessage,
-			}).Format())
+				errMessage,
+			)))
 			test.Fail()
 		}
 		return correct
 	}
 
 	printUnexpectedErr := func (err error) {
-		if err, ok := err.(*errors.Error); ok {
-			test.Log("lexer returned error:\n", err.Format())
-		} else {
-			test.Log("lexer returned error:", err)
-		}
+		test.Log("lexer returned error:\n" + errors.Format(err))
 	}
 
 	reader := strings.NewReader(input)