ToDo: Fix Me
- Python 3.3 or higher
pyvenv /PATH/TO/pstone
source /PATH/TO/pstone/bin/activate
primary : "(" expr ")" | NUMBER | IDENTIFIER | STRING
factor : "-" primary | primary
expr : factor { OP factor }
block : "{" [ statement ] {(";" | EOL) [ statement ]} "}"
simple : expr
statement : "if" expr block [ "else" block ]
| "while" expr block
| simple
program : [ statement ] (";" | EOL)