Consider the following BNF grammar: EXP ::= EXP + TERM | EXP - TERM | TERM TERM

Question

Consider the following BNF grammar:

EXP    ::= EXP + TERM   | EXP - TERM    | TERM

       TERM   ::= TERM * FACTOR | TERM / FACTOR | FACTOR

       FACTOR ::= ( EXP ) | DIGIT

       DIGIT ::= 0 | 1 | 2 | 3

Write a recursive descent recognizer pseudocode with:
- Ask the user for an input stream.
        - Report "legal" or "errors found", not both.
        - Assume the input stream is the token stream.
        - Assume the input stream terminates with a $.
        - Assume there is no white space.
        - Use a form to collect input and return the output.
        - Test your recognizer with illegal and legal strings.
        - Give a brief description of this recognizer for the user on how to use and what method that it based on.

Explanation / Answer

procedure exp() term() if token == ‘+’ match(‘+’) term() elseif token == ‘-‘ match(‘-‘) term() else break procedure term() factor() if token == ‘*’ match(‘*’) factor() elseif token == ‘/’ match(‘/’) factor() else break procedure factor() if token == ‘(‘ match(‘(‘) exp() match(‘)’) else digit() procedure digit() if token == ‘0’ match(‘0’) elseif token == ‘1’ match(‘1’) elseif token == ‘2’ match(‘2’) else match(‘3’) match(t) if token == t advancetokenpointer else error

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