QuickReview
sourcecodepartsofspeechwords
Scanner
code
specificationsScannerand
Generatortables
Previousclass:
→ Thescanneristhefirststageinthefrontend
→ Specificationscanbeexpressedusingregularexpressions
→ BuildtablesandcodefromaDFA
Goal
• Wewillshowhowtoconstructafinitestateautomatonto
recognizeanyRE
• ThisLecture
→ ConvertREtoannondeterministicfiniteautomaton(NFA)
Requiresε-transitionstocombineregularsubexpressions
→ ConvertanNFAtoadeterministicfiniteautomaton(DFA)
UseSubsetconstruction
NextLecture
→ Minimizethenumberofstates
Hopcroftstateminimizationalgorithm
→ Generatethescannercode
Additionalcodecanbeinserted
MoreRegularExpressions
• Allstringsof1sand0sendingina1
(0|1)*1
• Allstringsoverlowercaseletterswherethevowels(a,e,i,o,u)
occurexactlyonce,inascendingorder
Cons→(b|c|d|f|g|h|j|k|l|m|n|p|q|r|s|t|v|)
******
ConsaConseConsiConsoConsuCons
• Allstringsof1sand0sthatdonotcontainthree0sinarow:
MoreRegularExpressions
• Allstringsof1sand0sendingina1
(0|1)*1
• Allstringsoverlowercaseletterswherethevowels(a,e,i,o,u)
occurexactlyonce,inascendingorder
Cons→(b|c|d|f|g|h|j|k|l|m|n|p|q|r|s|t|v|)
******
ConsaConseConsiConsoConsuCons
• Allstringsof1sand0sthatdonotcontainthree0sinarow:
***
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