| author | Christian Urban <christian dot urban at kcl dot ac dot uk> |
| Fri, 27 Sep 2013 15:43:25 +0100 | |
| changeset 116 | 010ae7288327 |
| parent 93 | 4794759139ea |
| child 117 | 25999de692b2 |
| permissions | -rw-r--r-- |
| 7 | 1 |
def deriv (r: Rexp, c: Char) : Rexp = r match {
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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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case ALT(r1, r2) => ALT(deriv(r1, c), deriv(r2, c)) |
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case SEQ(r1, r2) => |
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if (nullable(r1)) ALT(SEQ(deriv(r1, c), r2), deriv(r2, c)) |
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else SEQ(deriv(r1, c), r2) |
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case STAR(r) => SEQ(deriv(r, c), STAR(r)) |
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} |
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