A Compiler for PL/0
<prog> → program <id>；<block>
<block> → [<condecl>][<vardecl>][<proc>]<body>
<condecl> → const <const>{,<const>};
<const> → <id>:=<integer>
<vardecl> → var <id>{,<id>};
<proc> → procedure <id>（[<id>{,<id>}]）;<block>{;<proc>}
<body> → begin <statement>{;<statement>}end
<statement> → <id> := <exp>
|if <lexp> then <statement>[else <statement>]
|while <lexp> do <statement>
|call <id>（[<exp>{,<exp>}]）
|<body>
|read (<id>{，<id>})
|write (<exp>{,<exp>})
<lexp> → <exp> <lop> <exp>|odd <exp>
<exp> → [+|-]<term>{<aop><term>}
<term> → <factor>{<mop><factor>}
<factor>→<id>|<integer>|(<exp>)
<lop> → =|<>|<|<=|>|>=
<aop> → +|-
<mop> → *|/
<id> → l{l|d} （ps：l for letters）
<integer> → d{d}
lexical.py: lexical analyzer
parser.py: grammer analyzer, semantic analyzer combined with code generater.It's also the main procedure
Pcodes.py: class for PseudoCode and class for its table
symbols.py: class for symbol and class for symbol table