diff -r e66bd5c563eb -r b5b5583a3a08 progs/parser1.scala
--- a/progs/parser1.scala	Mon Jul 27 11:02:48 2020 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,88 +0,0 @@
-// A naive bottom-up parser with backtracking
-//
-// Needs:
-//   :load matcher.scala
-
-// some regular expressions
-val DIGIT = RANGE("0123456789")
-val NONZERODIGIT = RANGE("123456789")
-
-val NUMBER = ALT(SEQ(NONZERODIGIT, STAR(DIGIT)), "0")
-val LPAREN = CHAR('(')
-val RPAREN = CHAR(')')
-val WHITESPACE = PLUS(RANGE(" \n"))
-val OPS = RANGE("+-*")
-
-// for classifying the strings that have been recognised
-
-abstract class Token
-case object T_WHITESPACE extends Token
-case object T_NUM extends Token
-case class T_OP(s: String) extends Token
-case object T_LPAREN extends Token
-case object T_RPAREN extends Token
-case class NT(s: String) extends Token
-
-// lexing rules for arithmetic expressions
-val lexing_rules: List[Rule[Token]]= 
-  List((NUMBER, (s) => T_NUM),
-       (WHITESPACE, (s) => T_WHITESPACE),
-       (LPAREN, (s) => T_LPAREN),
-       (RPAREN, (s) => T_RPAREN),
-       (OPS, (s) => T_OP(s.mkString)))
-
-// the tokenizer
-val Tok = Tokenizer(lexing_rules, List(T_WHITESPACE))
-
-type Grammar = List[(String, List[Token])]
-
-// grammar for arithmetic expressions
-val grammar = 
-  List ("F" -> List(T_NUM),
-        "E" -> List(T_NUM),
-        "E" -> List(NT("E"), T_OP("+"), NT("E")),
-        "E" -> List(NT("E"), T_OP("-"), NT("E")),
-        "E" -> List(NT("E"), T_OP("*"), NT("E")),    
-        "E" -> List(T_LPAREN, NT("E"), T_RPAREN))
-
-
-def chop[A](ts1: List[A], prefix: List[A], ts2: List[A]) : Option[(List[A], List[A])] = 
-  ts1 match {
-    case Nil => None
-    case t::ts => 
-      if (ts1.startsWith(prefix)) Some(ts2.reverse, ts1.drop(prefix.length))
-      else chop(ts, prefix, t::ts2)
-  }
-
-// examples for chop 
-chop(List(1,2,3,4,5,6,7,8,9), List(4,5), Nil)  
-chop(List(1,2,3,4,5,6,7,8,9), List(3,5), Nil)  
-
-def replace[A](ts: List[A], out: List[A], in: List [A]) = 
-  chop(ts, out, Nil) match {
-    case None => None
-    case Some((before, after)) => Some(before ::: in ::: after)
-  }  
-
-def parse(g: Grammar, ts: List[Token]) : Boolean = {
-  println(ts)
-  if (ts == List(NT("E"))) true
-  else {
-    val tss = for ((lhs, rhs) <- g) yield replace(ts, rhs, List(NT(lhs)))
-    tss.flatten.exists(parse(g, _))
-  }
-}
- 
-def parser(g: Grammar, s: String) = {
-  println("\n")
-  parse(g, Tok.fromString(s))
-}
-  
-
-
-parser(grammar, "2 + 3 *    4 +       1")
-parser(grammar, "(2 + 3) * (4 + 1)")
-parser(grammar, "(2 + 3) * 4 (4 + 1)")
-
-
-