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BNF is used in compiler design process. The diagram below summarizes the program writing method in Pascal.
<prog> ::= PROGRAM <prog-name> <element> BEGIN <statement list> END. <prog-name> ::= <ident> <ident> ::= <letter> | <letter><digit> <element> ::= VAR <dec-list> : <type> | CONST <dec-list> = <type> <dec-list> ::= <declaration> | <ident-list> : <type> <declaration> ::= <ident-list> : <type> <type> ::= INTEGER | STRING | REAL <ident-list> ::= ident | <ident-list> <statement list> ::= <statement> | <statement list> ; <statement> <statement> ::= <assign> | <input st> | <output st> | <defined loop> | <indefined loop> <assign> ::= <ident> := <expression> <expression> ::= <term> | <expression> + <term> | <expression> - <term> <condition statement> ::= IF <comparison> THEN <body> | IF <comparison> THEN <body> ELSE <body> <term> ::= <factor> | <term> * <factor> | <term> DIV <factor> <factor> ::= <ident> | int | ( <expression> ) <input st> ::= READ ( <ident-list> ) <output st> ::= WRITE ( <ident-list> ) <defined loop> ::= FOR <ident> := <expression> TO <expression> DO <body> <indefined loop> ::= WHILE <comparison> DO <body> | REPEAT <body> UNTIL <comparison> <comparison> ::= <expression> <relation> <expression> <relation> ::= = | < | <= | >= | <> <body> ::= <statement> | BEGIN <statement-list> END <letter> ::= a | b | ... | z | A | B | ... | Z <digit> ::= 0 | 1 | 2 | 3 | ... | 9 <procedure> ::= PROCEDURE <proc-name>(<dec-list>) VAR <dec-list> BEGIN <statement list> END <proc-name> ::= <ident> <function> ::= FUNCTION <func-name>(<dec-list>):<type> VAR <dec-list> BEGIN <statement list> END <func-name> ::= <ident>
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