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Christian Urban <christian dot urban at kcl dot ac dot uk>
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changeset
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1 |
def der (r: Rexp, c: Char) : Rexp = r match {
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7
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case NULL => NULL
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case EMPTY => NULL
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case CHAR(d) => if (c == d) EMPTY else NULL
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117
Christian Urban <christian dot urban at kcl dot ac dot uk>
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changeset
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case ALT(r1, r2) => ALT(der(r1, c), der(r2, c))
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case SEQ(r1, r2) =>
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117
Christian Urban <christian dot urban at kcl dot ac dot uk>
diff
changeset
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7 |
if (nullable(r1)) ALT(SEQ(der(r1, c), r2), der(r2, c))
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Christian Urban <christian dot urban at kcl dot ac dot uk>
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changeset
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8 |
else SEQ(der(r1, c), r2)
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Christian Urban <christian dot urban at kcl dot ac dot uk>
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changeset
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9 |
case STAR(r) => SEQ(der(r, c), STAR(r))
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7
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}
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117
Christian Urban <christian dot urban at kcl dot ac dot uk>
diff
changeset
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12 |
def ders (s: List[Char], r: Rexp) : Rexp = s match {
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Christian Urban <christian dot urban at kcl dot ac dot uk>
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changeset
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13 |
case Nil => r
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Christian Urban <christian dot urban at kcl dot ac dot uk>
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changeset
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14 |
case c::s => ders(s, der(c, r))
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Christian Urban <christian dot urban at kcl dot ac dot uk>
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changeset
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}
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Christian Urban <christian dot urban at kcl dot ac dot uk>
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changeset
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16 |
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