fixing issue#402
merge my partial work on fixing io
minor refactoring: hide empty constructors of KList and KSequence
fixing #146: incorrect compilation of ListBuiltin
resolved merging conflicts
reverted back trivial changes that remove trailing whitespaces
reverted unnecessary changes
Merge pull request #502 from yilongli/fixing-issue146

Fixing issue146 in unified-builtins2
Merge pull request #501 from yilongli/unified-builtins2

fixing #402 in branch Unified builtins2
conflict resolve