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1 def nullable (r: Rexp) : Boolean = r match { |
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2 case NULL => false |
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3 case EMPTY => true |
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4 case CHAR(_) => false |
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5 case ALT(r1, r2) => nullable(r1) || nullable(r2) |
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6 case SEQ(r1, r2) => nullable(r1) && nullable(r2) |
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7 case STAR(_) => true |
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8 } |