This should take no longer than 25 minutes and is simply intended to probe whether you have understood the material in the prac questions. YOU MAY NOT USE YOUR TEXTBOOK, NOTES OR A COMPUTER. Answer on the question sheet (3 sides). You may write in pencil if you like.
1. You were expecting this one, I bet! What are your name (surname) and student number? [1]
2. Part of the grammar for the extended Parva language you met in the practical might have been expressed as follows:
PRODUCTIONS
Parva = "void" "main" "(" ")" Block .
Block = "{" { Statement } "}" .
Statement = ( Block | WhileStatement | IfStatement | RepeatStatement
| ReadStatement | WriteStatement | Assignment
| ReturnStatement | EmptyStatement
| ConstDeclaration | VarDeclarations
).
IfStatement = "if" "(" Condition ")" Statement
{ "elseif" "(" Condition ")" Statement }
[ "else" Statement ] .
WhileStatement = "while" "(" Condition ")" Statement .
RepeatStatement = "repeat" { Statement } "until" "(" Condition ")" ";" .
What (if anything) would be the effect of replacing the productions as follows? [6]
Parva = "void" "main" "(" ")" Block .
Block = "{" { Declaration | Statement } "}" .
Declaration = ConstDeclaration | VarDeclarations .
Statement = ( WhileStatement | IfStatement | RepeatStatement
| ReadStatement | WriteStatement | Assignment
| ReturnStatement | EmptyStatement
).
IfStatement = "if" "(" Condition ")" Block
{ "elseif" "(" Condition ")" Block }
[ "else" Block ] .
WhileStatement = "while" "(" Condition ")" Block .
RepeatStatement = "repeat" Block "until" "(" Condition ")" ";" .
3. Show how one might specify a numeric literal in Cocol, allowing for the possibility of numbers of any of the following forms [4]
123 1.23 1. .23 1.2E12 1.2E-12 1E6 1E-6 .234E6 .234E-6
CHARACTERS
digit = "0123456789" .
TOKENS
number =
4. Develop a Cocol grammar for describing a list of Boolean expressions, like those you should remember from Boolean Algebra courses you may have taken. In this context, allow your Boolean expressions to be terminated with an = operator, and to include parentheses, single-letter variables, the constants FALSE and TRUE (sometimes written as 0 and 1), and the operators AND (written either as AND or "&&" or as a "dot", or simply omitted), OR (written either as OR or as "||" or as a "plus") and NOT, written either as a prefix NOT or as a suffix apostrophe. So some examples of Boolean expressions might be
a AND B OR (C OR NOT D) = a . b + (c + d') = a b + (c + d') =
NOT (a OR b) AND TRUE = (a + b)' . 1 = (a + b)' AND 1 =
b AND NOT C AND D = b . c' . d = b c' d =
Note that there is a precedence ordering among Boolean operators - parentheses take precedence over NOT, which takes precedence over AND, which takes precedence over OR. [8]
COMPILER Bool $CN
CHARACTERS
letter = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" .
TOKENS
variable = letter .
IGNORE CHR(0) .. CHR(31)
PRODUCTIONS
Bool = { Expression "=" } EOF .
Expression =
END Bool.
5. The PRODUCTIONS sections in your grammar should have made use of the EBNF "meta brackets" { } and [ ] in the production rules. How would you rewrite the PRODUCTIONS section without making any use of parentheses ( ) or of either of the { } or [ ] form of meta brackets? [6]
Hint: use right recursive productions, and assume that Cocol has a way of representing the empty string e.