1 import scala.language.implicitConversions |
|
2 import scala.language.reflectiveCalls |
|
3 |
|
4 // more convenience for the semantic actions later on |
|
5 case class ~[+A, +B](_1: A, _2: B) |
|
6 |
|
7 |
|
8 /* Note, in the lectures I did not show the implicit type consraint |
|
9 * I => Seq[_], which means that the input type 'I' needs to be |
|
10 * a sequence. */ |
|
11 |
|
12 type IsSeq[A] = A => Seq[_] |
|
13 |
|
14 abstract class Parser[I : IsSeq, T] { |
|
15 def parse(ts: I): Set[(T, I)] |
|
16 |
|
17 def parse_all(ts: I) : Set[T] = |
|
18 for ((head, tail) <- parse(ts); |
|
19 if tail.isEmpty) yield head |
|
20 } |
|
21 |
|
22 |
|
23 class SeqParser[I : IsSeq, T, S](p: => Parser[I, T], |
|
24 q: => Parser[I, S]) extends Parser[I, ~[T, S]] { |
|
25 def parse(sb: I) = |
|
26 for ((head1, tail1) <- p.parse(sb); |
|
27 (head2, tail2) <- q.parse(tail1)) yield (new ~(head1, head2), tail2) |
|
28 } |
|
29 |
|
30 class AltParser[I : IsSeq, T](p: => Parser[I, T], |
|
31 q: => Parser[I, T]) extends Parser[I, T] { |
|
32 def parse(sb: I) = p.parse(sb) ++ q.parse(sb) |
|
33 } |
|
34 |
|
35 class FunParser[I : IsSeq, T, S](p: => Parser[I, T], |
|
36 f: T => S) extends Parser[I, S] { |
|
37 def parse(sb: I) = |
|
38 for ((head, tail) <- p.parse(sb)) yield (f(head), tail) |
|
39 } |
|
40 |
|
41 // atomic parsers for characters, numbers and strings |
|
42 case class CharParser(c: Char) extends Parser[String, Char] { |
|
43 def parse(sb: String) = |
|
44 if (sb != "" && sb.head == c) Set((c, sb.tail)) else Set() |
|
45 } |
|
46 |
|
47 import scala.util.matching.Regex |
|
48 case class RegexParser(reg: Regex) extends Parser[String, String] { |
|
49 def parse(sb: String) = reg.findPrefixMatchOf(sb) match { |
|
50 case None => Set() |
|
51 case Some(m) => Set((m.matched, m.after.toString)) |
|
52 } |
|
53 } |
|
54 |
|
55 val NumParser = RegexParser("[0-9]+".r) |
|
56 def StringParser(s: String) = RegexParser(Regex.quote(s).r) |
|
57 |
|
58 // NumParserInt2 transforms a "string integer" into an Int; |
|
59 // needs new, because FunParser is not a case class |
|
60 |
|
61 val NumParserInt2 = new FunParser(NumParser, (s: String) => s.toInt) |
|
62 |
|
63 |
|
64 // convenience |
|
65 implicit def string2parser(s: String) = StringParser(s) |
|
66 implicit def char2parser(c: Char) = CharParser(c) |
|
67 |
|
68 implicit def ParserOps[I : IsSeq, T](p: Parser[I, T]) = new { |
|
69 def ||(q : => Parser[I, T]) = new AltParser[I, T](p, q) |
|
70 def ==>[S] (f: => T => S) = new FunParser[I, T, S](p, f) |
|
71 def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q) |
|
72 } |
|
73 |
|
74 implicit def StringOps(s: String) = new { |
|
75 def ||(q : => Parser[String, String]) = new AltParser[String, String](s, q) |
|
76 def ||(r: String) = new AltParser[String, String](s, r) |
|
77 def ==>[S] (f: => String => S) = new FunParser[String, String, S](s, f) |
|
78 def ~[S](q : => Parser[String, S]) = |
|
79 new SeqParser[String, String, S](s, q) |
|
80 def ~(r: String) = |
|
81 new SeqParser[String, String, String](s, r) |
|
82 } |
|
83 |
|
84 // NumParserInt can now be written as |
|
85 val NumParserInt = NumParser ==> (s => s.toInt) |
|
86 |
|
87 |
|
88 lazy val Pal : Parser[String, String] = |
|
89 (("a" ~ Pal ~ "a") ==> { case x ~ y ~ z => x + y + z } || |
|
90 ("b" ~ Pal ~ "b") ==> { case x ~ y ~ z => x + y + z } || "a" || "b" || "") |
|
91 |
|
92 Pal.parse_all("abaaaba") |
|
93 Pal.parse("abaaaba") |
|
94 |
|
95 println("Palindrome: " + Pal.parse_all("abaaaba")) |
|
96 |
|
97 // well-nested parentheses parser (transforms '(' -> '{' , ')' -> '}' ) |
|
98 lazy val P : Parser[String, String] = |
|
99 "(" ~ P ~ ")" ~ P ==> { case _ ~ x ~ _ ~ y => "{" + x + "}" + y } || "" |
|
100 |
|
101 P.parse_all("(((()()))())") |
|
102 P.parse_all("(((()()))()))") |
|
103 P.parse_all(")(") |
|
104 P.parse_all("()") |
|
105 |
|
106 // Arithmetic Expressions (Terms and Factors) |
|
107 |
|
108 lazy val E: Parser[String, Int] = |
|
109 (T ~ "+" ~ E) ==> { case x ~ _ ~ z => x + z } || |
|
110 (T ~ "-" ~ E) ==> { case x ~ _ ~ z => x - z } || T |
|
111 lazy val T: Parser[String, Int] = |
|
112 (F ~ "*" ~ T) ==> { case x ~ _ ~ z => x * z } || F |
|
113 lazy val F: Parser[String, Int] = |
|
114 ("(" ~ E ~ ")") ==> { case _ ~ y ~ _ => y } || NumParserInt |
|
115 |
|
116 /* same parser but producing a string |
|
117 lazy val E: Parser[String, String] = |
|
118 (T ~ "+" ~ E) ==> { case x ~ y ~ z => "(" + x + ")+(" + z + ")"} || T |
|
119 lazy val T: Parser[String, String] = |
|
120 (F ~ "*" ~ T) ==> { case x ~ y ~ z => "(" + x + ")*("+ z + ")"} || F |
|
121 lazy val F: Parser[String, String] = |
|
122 ("(" ~ E ~ ")") ==> { case x ~ y ~ z => y } || NumParser |
|
123 */ |
|
124 |
|
125 println(E.parse_all("1+3+4")) |
|
126 println(E.parse("1+3+4")) |
|
127 println(E.parse_all("4*2+3")) |
|
128 println(E.parse_all("4*(2+3)")) |
|
129 println(E.parse_all("(4)*((2+3))")) |
|
130 println(E.parse_all("4/2+3")) |
|
131 println(E.parse("1 + 2 * 3")) |
|
132 println(E.parse_all("(1+2)+3")) |
|
133 println(E.parse_all("1+2+3")) |
|
134 |
|
135 |
|
136 |
|
137 // no left-recursion allowed, otherwise will loop |
|
138 lazy val EL: Parser[String, Int] = |
|
139 (EL ~ "+" ~ EL ==> { case x ~ y ~ z => x + z} || |
|
140 EL ~ "*" ~ EL ==> { case x ~ y ~ z => x * z} || |
|
141 "(" ~ EL ~ ")" ==> { case x ~ y ~ z => y} || |
|
142 NumParserInt) |
|
143 |
|
144 //println(EL.parse_all("1+2+3")) |
|
145 |
|
146 |
|
147 |
|
148 |
|
149 // non-ambiguous vs ambiguous grammars |
|
150 |
|
151 // ambiguous |
|
152 lazy val S : Parser[String, String] = |
|
153 ("1" ~ S ~ S) ==> { case x ~ y ~ z => x + y + z } || "" |
|
154 |
|
155 S.parse("1" * 10) |
|
156 |
|
157 // non-ambiguous |
|
158 lazy val U : Parser[String, String] = |
|
159 ("1" ~ U) ==> { case x ~ y => x + y } || "" |
|
160 |
|
161 U.parse("1" * 25) |
|
162 |
|
163 U.parse("11") |
|
164 U.parse("11111") |
|
165 U.parse("11011") |
|
166 |
|
167 U.parse_all("1" * 100) |
|
168 U.parse_all("1" * 100 + "0") |
|
169 |
|
170 lazy val UCount : Parser[String, Int] = |
|
171 ("1" ~ UCount) ==> { case x ~ y => y + 1 } || "" ==> { x => 0 } |
|
172 |
|
173 UCount.parse("11111") |
|
174 UCount.parse_all("11111") |
|
175 |
|
176 |
|
177 |
|
178 // Single Character parser |
|
179 lazy val One : Parser[String, String] = "1" |
|
180 lazy val Two : Parser[String, String] = "2" |
|
181 |
|
182 One.parse("1") |
|
183 One.parse("111") |
|
184 |
|
185 (One ~ One).parse("111") |
|
186 (One ~ One ~ One).parse("111") |
|
187 (One ~ One ~ One ~ One).parse("1111") |
|
188 |
|
189 (One || Two).parse("111") |
|
190 |
|
191 |
|
192 |
|
193 // a problem with the arithmetic expression parser -> gets |
|
194 // slow with deeply nested parentheses |
|
195 println("Runtime problem") |
|
196 E.parse("1") |
|
197 E.parse("(1)") |
|
198 E.parse("((1))") |
|
199 E.parse("(((1)))") |
|
200 E.parse("((((1))))") |
|
201 E.parse("((((((1))))))") |
|
202 E.parse("(((((((1)))))))") |
|
203 E.parse("((((((((1)))))))") |
|