# HG changeset patch
# User Christian Urban <christian dot urban at kcl dot ac dot uk>
# Date 1462530801 -3600
# Node ID 6b0a1976f89a9cc6872712c35e6f2578b8bed301
# Parent  1b2b9000be88a9611a87d0c0cd789e4e19cfc9f1
added parser for regexes

diff -r 1b2b9000be88 -r 6b0a1976f89a progs/scala/tests.scala
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/scala/tests.scala	Fri May 06 11:33:21 2016 +0100
@@ -0,0 +1,83 @@
+import scala.language.implicitConversions    
+import scala.language.reflectiveCalls
+import scala.annotation.tailrec   
+import scala.io.Source
+import scala.util.parsing.combinator._
+
+abstract class Rexp 
+case object ZERO extends Rexp 
+case object ONE extends Rexp
+case class CHAR(c: Char) extends Rexp {
+  override def toString = c.toString 
+}
+case class ALT(r1: Rexp, r2: Rexp) extends Rexp {
+  override def toString = "(" + r1.toString + "|" + r2.toString + ")" 
+}
+case class SEQ(r1: Rexp, r2: Rexp) extends Rexp {
+  override def toString = "(" + r1.toString + r2.toString +")"
+} 
+case class STAR(r: Rexp) extends Rexp 
+case class RECD(x: String, r: Rexp) extends Rexp
+
+case class Parser(s: String) {
+  var i = 0
+  
+  def peek() = s(i)
+  def eat(c: Char) = 
+    if (c == s(i)) i = i + 1 else throw new Exception("Expected " + c + " got " + s(i))
+  def next() = { i = i + 1; s(i - 1) }
+  def more() = s.length - i > 0
+
+  def Regex() : Rexp = {
+    val t = Term();
+    if (more() && peek() == '|') {
+      eat ('|') ;
+      val r = Regex();
+      ALT(t, r) 
+    } 
+    else t
+  }
+
+  def Term() : Rexp = {
+    var f : Rexp = if (more() && peek() != ')' && peek() != '|') Factor() else ZERO;
+    while (more() && peek() != ')' && peek() != '|') {
+      var nextf = Factor();
+      f = SEQ(f, nextf) ;
+    }
+
+    f
+  }
+
+  def Factor() : Rexp = {
+    var b = Base();
+    while (more() && peek() == '*') {
+      eat('*') ;
+      b = STAR(b) ;
+    }
+
+    b
+  }
+
+  def Base() : Rexp = {
+    peek() match {
+      case '(' => { eat('(') ; val r = Regex(); eat(')') ; r }
+      case _ => CHAR(next())
+    }
+  }
+}
+
+println(Parser("a|(bc)*").Regex())
+
+
+def process(line: String) : String = {
+  val s = line.split("\\t+")(1)
+  s + ":   " + Parser(s).Regex().toString
+}
+
+
+val filename = "../tests/forced-assoc.txt"
+val filelines : List[String] = Source.fromFile(filename).getLines.toList
+
+
+filelines.foreach((s: String) => println(process(s)))
+