Program ::= Global Functions
;

Global ::= GLOBAL Var_decls END
        | /* empty */
;

Functions ::= Def_fun Functions
            | Def_fun
;

Def_fun ::= FUNCTION ID LPAR Par_decls RPAR COLON TypeDenoter Statements END
          | FUNCTION ID LPAR RPAR COLON TypeDenoter Statements END
;

Par_decls ::= ID COLON TypeDenoter COMMA Par_decls
            | ID COLON TypeDenoter
;

Var_decls ::= Var_decls SEMI ID COLON TypeDenoter Var_init_value  
            | ID COLON TypeDenoter Var_init_value
;

Var_init_value ::= ASSIGN Expr
                | /* empty */
;

TypeDenoter ::= NIL | INT | BOOL | FLOAT | STRING
      | BLPAR TypeDenoter BRPAR
      | LPAR Types RPAR ARROW TypeDenoter
      | LPAR RPAR ARROW TypeDenoter
;

Types ::= TypeDenoter COMMA Types
        | TypeDenoter
;

Statements ::= Stat SEMI Statements
            | Stat
;

Stat ::= NOP
      | WHILE Expr DO Statements END
      | IF Expr THEN Statements END
      | IF Expr THEN Statements ELSE Statements END
      | FOR ID ASSIGN Expr COMMA Expr DO Statements END
      | LOCAL Var_decls SEMI Statements END
      | ID ASSIGN Expr
      | Expr SLPAR Expr SRPAR ASSIGN Expr
      | ID LPAR Exprs RPAR
      | ID LPAR RPAR
      | Vars READ
      | Exprs WRITE
      | RETURN Expr
      | error
;

Vars ::= ID COMMA Vars
      | ID
;

Exprs ::= Expr COMMA Exprs
        | Expr
;

Expr ::=  NIL 
      | TRUE 
      | FALSE 
      | INT_CONST 
      | FLOAT_CONST 
      | STRING_CONST 
      | BLPAR BRPAR COLON TypeDenoter 
      | ID 
      | Expr SLPAR Expr SRPAR 
      | ID LPAR Exprs RPAR
      | ID LPAR RPAR
      | Expr PLUS Expr 
      | Expr MINUS Expr 
      | Expr TIMES Expr 
      | Expr DIV Expr 
      | Expr AND Expr 
      | Expr OR Expr 
      | Expr GT Expr 
      | Expr GE Expr 
      | Expr LT Expr 
      | Expr LE Expr 
      | Expr EQ Expr 
      | Expr NE Expr 
      | MINUS Expr 
      | NOT Expr 
      | SHARP Expr
        
;