fixed a bug where error messages were being swallowed.
added L4.
added in some error handling
fixed a bug in showing let statements in L3AST
renamed changeExtension to changeExt, fixed a minor bug in getDir on files in the current directory.
minor refactoring
renamed changeExtension to changeExt, fixed a minor bug in getDir on files in the current directory.
lots of refactoring
removed oops