8 |
8 |
9 // Note, in the lectures I did not show the type bound |
9 // Note, in the lectures I did not show the type bound |
10 // using is: I => Seq[_], which means that the input |
10 // using is: I => Seq[_], which means that the input |
11 // type 'I' needs to be a sequence. |
11 // type 'I' needs to be a sequence. |
12 |
12 |
13 abstract class Parser[I, T](using is: I => Seq[_]) { |
13 type IsSeq[I] = I => Seq[_] |
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14 |
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15 abstract class Parser[I, T](using is: IsSeq[I]) { |
14 def parse(in: I): Set[(T, I)] |
16 def parse(in: I): Set[(T, I)] |
15 |
17 |
16 def parse_all(in: I) : Set[T] = |
18 def parse_all(in: I) : Set[T] = |
17 for ((hd, tl) <- parse(in); |
19 for ((hd, tl) <- parse(in); |
18 if is(tl).isEmpty) yield hd |
20 if is(tl).isEmpty) yield hd |
19 } |
21 } |
20 |
22 |
21 // parser combinators |
23 // parser combinators |
22 |
24 |
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25 |
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26 |
23 // alternative parser |
27 // alternative parser |
24 class AltParser[I, T](p: => Parser[I, T], |
28 class AltParser[I : IsSeq, T](p: => Parser[I, T], |
25 q: => Parser[I, T])(using I => Seq[_]) extends Parser[I, T] { |
29 q: => Parser[I, T]) extends Parser[I, T] { |
26 def parse(in: I) = p.parse(in) ++ q.parse(in) |
30 def parse(in: I) = p.parse(in) ++ q.parse(in) |
27 } |
31 } |
28 |
32 |
29 // sequence parser |
33 // sequence parser |
30 class SeqParser[I, T, S](p: => Parser[I, T], |
34 class SeqParser[I: IsSeq, T, S](p: => Parser[I, T], |
31 q: => Parser[I, S])(using I => Seq[_]) extends Parser[I, (T, S)] { |
35 q: => Parser[I, S]) extends Parser[I, (T, S)] { |
32 def parse(in: I) = |
36 def parse(in: I) = |
33 for ((hd1, tl1) <- p.parse(in); |
37 for ((hd1, tl1) <- p.parse(in); |
34 (hd2, tl2) <- q.parse(tl1)) yield ((hd1, hd2), tl2) |
38 (hd2, tl2) <- q.parse(tl1)) yield ((hd1, hd2), tl2) |
35 } |
39 } |
36 |
40 |
37 // map parser |
41 // map parser |
38 class MapParser[I, T, S](p: => Parser[I, T], |
42 class MapParser[I : IsSeq, T, S](p: => Parser[I, T], |
39 f: T => S)(using I => Seq[_]) extends Parser[I, S] { |
43 f: T => S) extends Parser[I, S] { |
40 def parse(in: I) = for ((hd, tl) <- p.parse(in)) yield (f(hd), tl) |
44 def parse(in: I) = for ((hd, tl) <- p.parse(in)) yield (f(hd), tl) |
41 } |
45 } |
42 |
46 |
43 |
47 |
44 |
48 |
84 |
88 |
85 |
89 |
86 (p"else").parse("elsethen") |
90 (p"else").parse("elsethen") |
87 |
91 |
88 // more convenient syntax for parser combinators |
92 // more convenient syntax for parser combinators |
89 extension [I, T](p: Parser[I, T])(using I => Seq[_]) { |
93 extension [I: IsSeq, T](p: Parser[I, T]) { |
90 def ||(q : => Parser[I, T]) = new AltParser[I, T](p, q) |
94 def ||(q : => Parser[I, T]) = new AltParser[I, T](p, q) |
91 def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q) |
95 def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q) |
92 def map[S](f: => T => S) = new MapParser[I, T, S](p, f) |
96 def map[S](f: => T => S) = new MapParser[I, T, S](p, f) |
93 } |
97 } |
94 |
98 |