10 case class CHAR(c: Char) extends Rexp |
10 case class CHAR(c: Char) extends Rexp |
11 case class ALTs(rs: List[Rexp]) extends Rexp // alternatives |
11 case class ALTs(rs: List[Rexp]) extends Rexp // alternatives |
12 case class SEQ(r1: Rexp, r2: Rexp) extends Rexp // sequence |
12 case class SEQ(r1: Rexp, r2: Rexp) extends Rexp // sequence |
13 case class STAR(r: Rexp) extends Rexp // star |
13 case class STAR(r: Rexp) extends Rexp // star |
14 |
14 |
15 import scala.language.implicitConversions |
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16 import scala.language.reflectiveCalls |
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17 |
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18 def charlist2rexp(s: List[Char]): Rexp = s match { |
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19 case Nil => ONE |
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20 case c::Nil => CHAR(c) |
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21 case c::s => SEQ(CHAR(c), charlist2rexp(s)) |
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22 } |
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23 implicit def string2rexp(s: String): Rexp = charlist2rexp(s.toList) |
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24 |
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25 |
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26 // "a|b" |
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27 ALT(CHAR('a'), CHAR('b')) |
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28 |
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29 val reg : Rexp = "a" | "b" // CHAR('a') |
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30 |
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31 // some convenience for typing regular expressions |
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32 |
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33 //the usual binary choice can be defined in terms of ALTs |
15 //the usual binary choice can be defined in terms of ALTs |
34 def ALT(r1: Rexp, r2: Rexp) = ALTs(List(r1, r2)) |
16 def ALT(r1: Rexp, r2: Rexp) = ALTs(List(r1, r2)) |
35 |
17 |
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18 |
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19 // some convenience for typing regular expressions |
36 |
20 |
37 import scala.language.implicitConversions |
21 import scala.language.implicitConversions |
38 import scala.language.reflectiveCalls |
22 import scala.language.reflectiveCalls |
39 |
23 |
40 def charlist2rexp(s: List[Char]): Rexp = s match { |
24 def charlist2rexp(s: List[Char]): Rexp = s match { |
41 case Nil => ONE |
25 case Nil => ONE |
42 case c::Nil => CHAR(c) |
26 case c::Nil => CHAR(c) |
43 case c::s => SEQ(CHAR(c), charlist2rexp(s)) |
27 case c::s => SEQ(CHAR(c), charlist2rexp(s)) |
44 } |
28 } |
45 implicit def string2rexp(s: String): Rexp = charlist2rexp(s.toList) |
29 implicit def string2rexp(s: String): Rexp = charlist2rexp(s.toList) |
46 |
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47 |
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48 |
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49 |
30 |
50 implicit def RexpOps (r: Rexp) = new { |
31 implicit def RexpOps (r: Rexp) = new { |
51 def | (s: Rexp) = ALT(r, s) |
32 def | (s: Rexp) = ALT(r, s) |
52 def % = STAR(r) |
33 def % = STAR(r) |
53 def ~ (s: Rexp) = SEQ(r, s) |
34 def ~ (s: Rexp) = SEQ(r, s) |
58 def | (r: String) = ALT(s, r) |
39 def | (r: String) = ALT(s, r) |
59 def % = STAR(s) |
40 def % = STAR(s) |
60 def ~ (r: Rexp) = SEQ(s, r) |
41 def ~ (r: Rexp) = SEQ(s, r) |
61 def ~ (r: String) = SEQ(s, r) |
42 def ~ (r: String) = SEQ(s, r) |
62 } |
43 } |
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44 |
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45 |
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46 // ALT(CHAR('a'), CHAR('b')) |
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47 // val reg : Rexp = "a" | "b" |
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48 |
63 |
49 |
64 // (1) Complete the function nullable according to |
50 // (1) Complete the function nullable according to |
65 // the definition given in the coursework; this |
51 // the definition given in the coursework; this |
66 // function checks whether a regular expression |
52 // function checks whether a regular expression |
67 // can match the empty string and Returns a boolean |
53 // can match the empty string and Returns a boolean |