Consider the following BNF grammar that describes some of the \"technical electi

Question

 Consider the following BNF grammar that describes    some of the "technical elective" courses allowed by the CS degree    plan.     <tech-electives> -> <tech-courses>    <tech-courses> -> <tech-course> | <tech-course> <tech-courses>    <tech-course> -> CS4390 | CS4371 | CS4373                      | CS4330 | CS4317 | CS4339 | CS4342     You need to take at least five technical elective courses. However,    no more than two courses of CS4390 (Special Topics), CS4371    (Independent Studies) and CS4373 (Internship) in any combination    can count for technical electives.         CS4390 CS4330 CS4317 CS4339 CS4342 -- ok: one special course    CS4390 CS4390 CS4317 CS4339 CS4342 -- ok: two    CS4390 CS4371 CS4317 CS4339 CS4342 -- ok: two    CS4390 CS4390 CS4390 CS4330 CS4317 CS4339 -- ok: why?    CS4390 CS4330 CS4317               -- not okay: < five    CS4390 CS4390 CS4373 CS4330 CS4342 -- not okay: three      Extend the given BNF grammar to an attribute grammar to    specify the above rules. 

Explanation / Answer

The Backus-Naur Form is a way of defining syntax. It consists of

• a set of terminal symbols
• a set of non-terminal symbols
• a set of production rules of the form

LHS = RHS.

LHS-> left hand side , RHS -> Right hand side.

The meaning of the production rule is that the non-terminal on the left hand side may be replaced by the expression on the right hand side.

According to the production rule, we can also right the above expression as follow

<tech-electives> ::= <tech-courses>
<tech-courses> ::=<tech-course> | <tech-course> <tech-courses>
<tech-course> ::= CS4390 | CS4371 | CS4373
| CS4330 | CS4317 | CS4339 | CS4342
<case-statement> ::=case <select five tech-course> of <course-list> | {; <course-list>} end

<select five tech-course> ::= if((CS4390<=2) and (CS4371) and (CS4373))
<course-list>::=<one special-courses> |<two-course> | <two-courses> |<Why particular-courses> |<Less than five-courses> |<Three-courses>
<one special-courses> :: = 'CS4390' | 'CS4330' | 'CS4317' | 'CS4339' | 'CS4342'
<two-course>:: = 'CS4390' | 'CS4390' | 'CS4317' | 'CS4339' | 'CS4342'
<two-courses>:: = 'CS4390' | 'CS4371' | 'CS4317' | 'CS4339' | 'CS4342'
<Why particular-courses>:: = 'CS4390' | 'CS4390' | 'CS4390' | 'CS4330' | 'CS4317'| 'CS4339'
<Less than five-courses>:: = 'CS4390' | 'CS4330' | 'CS4317'
<Three-courses>:: = 'CS4390' | 'CS4390' | 'CS4373' | 'CS4330' | 'CS4342'

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