Top-down Parsing (ASU Ch 4.4) Predictive Parsers (ASU 4.4 ...

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First and Follow Sets (ASU Ch 4.4) • first(X) – if X is T first(X) is { X } – if X ¤ in P first(X) += ¤ (¤ = empty) – if X is NT and X Y 1 Y 2 Y 3 …Y n in P • first(X) += a if a in first(Y i ) and ¤ in first(Y 1 ) … first(Y i-1 ) – i.e. Y 1 Y 2 Y 3 …Y i-1 ¤ – if ¤ in first(Y 1 ) … first(Y k ) first(X) += ¤ – first(X) += first(Y 1 ) if not Y 1 ¤ – first(X) += first(Y 2 ) if Y 1 ¤ and not Y 2 ¤ – and so on ... – continued on next slide 8 14/10/2014 DFR - CC - TDP
First and Follow Sets (ASU Ch 4.4) • first(X) continued (the implications of ¤) – for any string X 1 X 2 X 3 … X n • first( X 1 X 2 X 3 … X n ) += non ¤ symbols in first( X 1 ) • if ¤ in first( X 1 ) – first( X 1 X 2 X 3 … X n ) += non ¤ symbols in first( X 2 ) • if ¤ in first( X 1 ) and ¤ in first( X 2 ) – first( X 1 X 2 X 3 … X n ) += non ¤ symbols in first( X 3 ) – and so on • if ¤ in first( X i ) i = 1..n, first( X 1 X 2 X 3 … X n ) += ¤ 9 14/10/2014 DFR - CC - TDP
Page 1 and 2: Top-down Parsing (ASU Ch 4.4) • P
Page 3 and 4: Transition Diagrams (ASU pp183-185)
Page 5 and 6: Recursive Descent example L ::= E {
Page 7: Non Recursive Predictive Parser (NR
Page 11 and 12: First and Follow Sets (ASU Ch 4.4)
Page 13 and 14: Parsing Table M (ASU Fig 4.15 p188)
Page 15 and 16: Constructing the Parsing Table: Det
Page 17 and 18: Non Recursive Parsing Algorithm (AS
Page 19 and 20: Properties of LL(1) Grammars (ASU C

Top-down Parsing (ASU Ch 4.4) Predictive Parsers (ASU 4.4 ...

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