Download CS 401/501 Exam: Token vs Lexeme, Regex, BNF Grammar, Parser, Attribute Grammar and more Exams Programming Languages in PDF only on Docsity! CS 401/501 EXAM #1 SAMPLE QUESTIONS WITH SOLUTIONS 1. Explain the difference between a token and a lexeme. (5%) The lowest-level syntactic units are called lexemes. Lexemes are partitioned into groups (identifiers, keywords, operators, separators, literals). Each lexeme group is represented by a token. 2. For each regular expression below provide a brief description what kind of lexemes are going to match with a pattern and provide some examples of lexemes (at least 3). [pr]?ink [a-z][a-z0-9]* [1-9][0-9][0-9] /\*[^\*]+\*/ ([a-c][0-9])+ (10%) Keywords: pink, rink, ink Identifiers, which consist of letters (only alphabetic characters) and digits with the restrictions that it must begin with a letter: b counter i20 3-digit numbers with the restriction that first digit is not 0: 100 999 123 Multiline comment: /* abc */ /* this is comment */ /* */ Sequence of letters a-c and digits: a1 b0c3 c9c8c7b6 3. Write a BNF grammar for a language, in which programs always start with the keyword “print” followed by arithmetic expression (+ or -). The later is optionally followed by a declaration part, starting with the keyword “where” and a list of pairs “id=num” which are separated with “,”. Few examples: print 10 print a+10 where a=1 print a+b-c where a=2, b=4, c=21 (20%) P ::= print E D E ::= E + T | E - T | T T ::= ( E ) | num | id D ::= where F | ε F ::= id = num G G ::= , F | ε 4. Perform left factoring on the production B ::= spring A | spring num C (5%) B ::= spring BB BB ::= A | num C 5. Write a recursive descent parser for the following LL(1) grammar. Assume the existence of a scanning procedure GET_TOKEN which sets a global string variable TOKEN to the token type of the next token. P ::= D begin S end D ::= var V V::= T V | ε T ::= int id ; | real id ; S ::= id := num S | ε Draw a parse tree for the sentence: var int i; int j; begin end (25+5%) procedure main GET_TOKEN call P if TOKEN <> EOF then ERROR endif end procedure P call D if TOKEN=begin then GET_TOKEN else ERROR endif call S if TOKEN=end the GET_TOKEN else ERROR endif end procedure D if TOKEN=var then GET_TOKEN else ERROR endif call V end procedure V if TOKEN=int || TOKEN=real then call T call V endif end procedure T if TOKEN=int then GET_TOKEN if TOKEN=id then GET_TOKEN else ERROR endif if TOKEN=; then GET_TOKEN else ERROR endif else if TOKEN=real then GET_TOKEN if TOKEN=id then GET_TOKEN else ERROR endif
