7
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1 |
def deriv (r: Rexp, c: Char) : Rexp = r match {
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2 |
case NULL => NULL
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3 |
case EMPTY => NULL
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4 |
case CHAR(d) => if (c == d) EMPTY else NULL
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5 |
case ALT(r1, r2) => ALT(deriv(r1, c), deriv(r2, c))
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6 |
case SEQ(r1, r2) =>
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7 |
if (nullable(r1)) ALT(SEQ(deriv(r1, c), r2), deriv(r2, c))
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8 |
else SEQ(deriv(r1, c), r2)
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9 |
case STAR(r) => SEQ(deriv(r, c), STAR(r))
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10 |
}
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11 |
|