DOC
a simple stack
a simple unit test for stack
basic calculator that is able to print its state
binary operators
negation operator
copy operator
use exceptions instead of printing error messages
delete operator
formatting
cleaner way of printing stack; make clear how stack.toString works
raise an error if the calculator can't interpret a token
implement the exit command
the top most element of a stack is now always printed as left-most element and is at index 0
read and write commands
simplify
allow blocks on stacks
test if block is pushed to data stack correctly
operator apply
test w with invalid argument on data stack