Pascal’s Backus Naur Form (BNF)
BNF is used in compiler design process. This diagram 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>