- class 'Parsers' is used by parsers1.scala and...

- class 'Parsers' is used by parsers1.scala and typeinf.scala.

1 files changed, 118 insertions, 0 deletions

diff --git a/sources/examples/Parsers.scala b/sources/examples/Parsers.scala
new file mode 100644
index 0000000000..582ad5b1f9
--- /dev/null
+++ b/sources/examples/Parsers.scala
@@ -0,0 +1,118 @@
+package examples;
+
+object parsers {
+
+abstract class Parsers {
+
+  type intype;
+
+  abstract class Parser {
+
+    type Result = Option[intype];
+
+    def apply(in: intype): Result;
+
+    /*** p &&& q applies first p, and if that succeeds, then q
+     */
+    def &&& (def q: Parser) = new Parser {
+      def apply(in: intype): 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 ||| (def q: Parser) = new Parser {
+      def apply(in: intype): Result = Parser.this.apply(in) match {
+        case None => q(in)
+        case s => s
+      }
+    }
+  }
+
+  val empty = new Parser {
+    def apply(in: intype): Result = Some(in)
+  }
+
+  val fail = new Parser {
+    def apply(in: intype): 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 intype = 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)"))
+  }
+
+}