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CS 442/542

CS 442/542. Parsing Part 2. Quiz 6 Problems and definitions. Definitions Regular Expression, NFA, DFA, CGF, First Set, Follow Set, First + Problems

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CS 442/542

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  1. CS 442/542 Parsing Part 2

  2. Quiz 6 Problems and definitions • Definitions • Regular Expression, NFA, DFA, CGF, First Set, Follow Set, First+ • Problems • Create RE to specify a language, build NFA from RE, build DFA from NFA using the subset construction, build a minimized DFA from a DFA, create and RE that specifies the strings recognized by a DFA. Write simple lex/C code segments

  3. First Set • For any grammar symbol α, First(α) is the set of terminals that can appear at the start of a sentence derived from α

  4. Follow Set • For any nonterminal α, Follow(α) is the set of terminals that can occur immediately α in a sentence

  5. First+ • First+(A ->β ) = { t | if ε ∉ First(β) then t ∈First(β) else t ∈First(β) U Follow(A)} • Also called the Predict set • Note this definition includes ε in the First+ set some definitions exclude it and in the way this set will be used in the algorithm to build the LL(1) parse table ε will not be important

  6. Build First Set

  7. Build the First Sets for the Following Grammar 1. S -> B 2. B -> B1 B2 3. B2 -> OR B1 B2 4. B2 -> ε 5. B1 -> B3 B4 6. B4 -> AND B3 B4 7. B4 -> ε 8. B3 -> VAR

  8. Build Follow Sets

  9. Build LL(1) Parse Table

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