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author | Gilles Dubochet <gilles.dubochet@epfl.ch> | 2005-12-16 18:44:33 +0000 |
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committer | Gilles Dubochet <gilles.dubochet@epfl.ch> | 2005-12-16 18:44:33 +0000 |
commit | 53a3cc7b17f4cf97075b7e71720777fd84109696 (patch) | |
tree | 0cc784e0b47ea49cc151a136d19f20bfa8ee2197 /docs/examples/parsers1.scala | |
parent | df50e05006b43b007c2587549030d24b5c154398 (diff) | |
download | scala-53a3cc7b17f4cf97075b7e71720777fd84109696.tar.gz scala-53a3cc7b17f4cf97075b7e71720777fd84109696.tar.bz2 scala-53a3cc7b17f4cf97075b7e71720777fd84109696.zip |
Created proper 'docs' folder for new layout.
Diffstat (limited to 'docs/examples/parsers1.scala')
-rw-r--r-- | docs/examples/parsers1.scala | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/docs/examples/parsers1.scala b/docs/examples/parsers1.scala new file mode 100644 index 0000000000..143f354049 --- /dev/null +++ b/docs/examples/parsers1.scala @@ -0,0 +1,118 @@ +package examples; + +object parsers1 { + + abstract class Parsers { + + type inputType; + + abstract class Parser { + + type Result = Option[inputType]; + + def apply(in: inputType): Result; + + /*** p &&& q applies first p, and if that succeeds, then q + */ + def &&& (q: => Parser) = new Parser { + def apply(in: inputType): Result = Parser.this.apply(in) match { + case None => None + case Some(in1) => q(in1) + } + } + + /*** p ||| q applies first p, and, if that fails, then q. + */ + def ||| (q: => Parser) = new Parser { + def apply(in: inputType): Result = Parser.this.apply(in) match { + case None => q(in) + case s => s + } + } + } + + val empty = new Parser { + def apply(in: inputType): Result = Some(in) + } + + val fail = new Parser { + def apply(in: inputType): Result = None + } + + def opt(p: Parser): Parser = p ||| empty; // p? = (p | <empty>) + def rep(p: Parser): Parser = opt(rep1(p)); // p* = [p+] + def rep1(p: Parser): Parser = p &&& rep(p); // p+ = p p* + } + + abstract class ListParsers extends Parsers { + def chr(p: char => boolean): Parser; + def chr(c: char): Parser = chr(d: char => d == c); + + def letter : Parser = chr(Character.isLetter); + def digit : Parser = chr(Character.isDigit); + + def ident : Parser = letter &&& rep(letter ||| digit); + def number : Parser = digit &&& rep(digit); + def list : Parser = chr('(') &&& listElems &&& chr(')'); + def listElems : Parser = expr &&& (chr(',') &&& listElems ||| empty); + def expr : Parser = ident ||| number ||| list; + } + + abstract class ExprParsers extends Parsers { + def chr(p: char => boolean): Parser; + def chr(c: char): Parser = chr(d: char => d == c); + + def digit : Parser = chr(Character.isDigit); + def number : Parser = digit &&& rep(digit); + def summand : Parser = number ||| chr('(') &&& expr &&& chr(')'); + def expr : Parser = summand &&& rep(chr('+') &&& summand) + } + + class ParseString(s: String) extends Parsers { + type inputType = int; + val input = 0; + def chr(p: char => boolean) = new Parser { + def apply(in: int): Parser#Result = + if (in < s.length() && p(s charAt in)) Some(in + 1); + else None; + } + } + + object TestList { + + def main(args: Array[String]): unit = + if (args.length == 1) { + val ps = new ListParsers with ParseString(args(0)); + ps.expr(ps.input) match { + case Some(n) => + Console.println("parsed: " + args(0).substring(0, n)); + case None => + Console.println("nothing parsed"); + } + } + else + Console.println("usage: java examples.TestList <expr-string>"); + } + + object TestExpr { + + def main(args: Array[String]): unit = + if (args.length == 1) { + val ps = new ExprParsers with ParseString(args(0)); + ps.expr(ps.input) match { + case Some(n) => + Console.println("parsed: " + args(0).substring(0, n)); + case None => + Console.println("nothing parsed"); + } + } + else + Console.println("usage: java examples.TestExpr <expr-string>"); + } + + def main(args: Array[String]): Unit = { + TestList.main(Array("(a,b,(1,2))")); + TestExpr.main(Array("2+3+(4+1)")) + } + +} |