diff -r 47f86885d481 -r e85600529ca5 while.scala
--- a/while.scala	Sun Dec 23 00:38:56 2012 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,231 +0,0 @@
-// A parser and evaluator for teh while language
-// 
-import matcher._
-import parser._
-
-
-// some regular expressions
-val SYM = RANGE("ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz_")
-val DIGIT = RANGE("0123456789")
-val ID = SEQ(SYM, STAR(ALT(SYM, DIGIT))) 
-val NUM = PLUS(DIGIT)
-val KEYWORD = ALTS("skip", "while", "do", "if", "then", "else", "true", "false") 
-val SEMI: Rexp = ";"
-val OP: Rexp = ALTS(":=", "=", "-", "+", "*", "!=", "<", ">")
-val WHITESPACE = PLUS(RANGE(" \n"))
-val RPAREN: Rexp = ")"
-val LPAREN: Rexp = "("
-val BEGIN: Rexp = "{"
-val END: Rexp = "}"
-
-// tokens for classifying the strings that have been recognised
-abstract class Token
-case object T_WHITESPACE extends Token
-case object T_SEMI extends Token
-case object T_LPAREN extends Token
-case object T_RPAREN extends Token
-case object T_BEGIN extends Token
-case object T_END extends Token
-case class T_ID(s: String) extends Token
-case class T_OP(s: String) extends Token
-case class T_NUM(s: String) extends Token
-case class T_KWD(s: String) extends Token
-
-val lexing_rules: List[(Rexp, List[Char] => Token)] = 
-  List((KEYWORD, (s) => T_KWD(s.mkString)),
-       (ID, (s) => T_ID(s.mkString)),
-       (OP, (s) => T_OP(s.mkString)),
-       (NUM, (s) => T_NUM(s.mkString)),
-       (SEMI, (s) => T_SEMI),
-       (LPAREN, (s) => T_LPAREN),
-       (RPAREN, (s) => T_RPAREN),
-       (BEGIN, (s) => T_BEGIN),
-       (END, (s) => T_END),
-       (WHITESPACE, (s) => T_WHITESPACE))
-
-// the tokenizer
-val Tok = Tokenizer(lexing_rules, List(T_WHITESPACE))
-
-// the abstract syntax trees
-abstract class Stmt
-abstract class AExp
-abstract class BExp 
-type Block = List[Stmt]
-case object Skip extends Stmt
-case class If(a: BExp, bl1: Block, bl2: Block) extends Stmt
-case class While(b: BExp, bl: Block) extends Stmt
-case class Assign(s: String, a: AExp) extends Stmt
-
-case class Var(s: String) extends AExp
-case class Num(i: Int) extends AExp
-case class Aop(o: String, a1: AExp, a2: AExp) extends AExp
-
-case object True extends BExp
-case object False extends BExp
-case class Bop(o: String, a1: AExp, a2: AExp) extends BExp
-
-// atomic parsers
-case class TokParser(tok: Token) extends Parser[List[Token], Token] {
-  def parse(ts: List[Token]) = ts match {
-    case t::ts if (t == tok) => Set((t, ts)) 
-    case _ => Set ()
-  }
-}
-implicit def token2tparser(t: Token) = TokParser(t)
-
-case object NumParser extends Parser[List[Token], Int] {
-  def parse(ts: List[Token]) = ts match {
-    case T_NUM(s)::ts => Set((s.toInt, ts)) 
-    case _ => Set ()
-  }
-}
-
-case object IdParser extends Parser[List[Token], String] {
-  def parse(ts: List[Token]) = ts match {
-    case T_ID(s)::ts => Set((s, ts)) 
-    case _ => Set ()
-  }
-}
-
-
-// arithmetic expressions
-lazy val AExp: Parser[List[Token], AExp] = 
-  (T ~ T_OP("+") ~ AExp) ==> { case ((x, y), z) => Aop("+", x, z): AExp } ||
-  (T ~ T_OP("-") ~ AExp) ==> { case ((x, y), z) => Aop("-", x, z): AExp } || T  
-lazy val T: Parser[List[Token], AExp] = 
-  (F ~ T_OP("*") ~ T) ==> { case ((x, y), z) => Aop("*", x, z): AExp } || F
-lazy val F: Parser[List[Token], AExp] = 
-  (T_LPAREN ~> AExp <~ T_RPAREN) || 
-  IdParser ==> Var || 
-  NumParser ==> Num
-
-// boolean expressions
-lazy val BExp: Parser[List[Token], BExp] = 
-  (AExp ~ T_OP("=") ~ AExp) ==> { case ((x, y), z) => Bop("=", x, z): BExp } || 
-  (AExp ~ T_OP("!=") ~ AExp) ==> { case ((x, y), z) => Bop("!=", x, z): BExp } || 
-  (AExp ~ T_OP("<") ~ AExp) ==> { case ((x, y), z) => Bop("<", x, z): BExp } || 
-  (AExp ~ T_OP(">") ~ AExp) ==> { case ((x, y), z) => Bop(">", x, z): BExp } || 
-  (T_KWD("true") ==> ((_) => True)) || 
-  (T_KWD("false") ==> ((_) => False: BExp))
-
-lazy val Stmt: Parser[List[Token], Stmt] =
-  (T_KWD("skip") ==> ((_) => Skip: Stmt)) ||
-  (IdParser ~ T_OP(":=") ~ AExp) ==> { case ((x, y), z) => Assign(x, z): Stmt } ||
-  (T_KWD("if") ~ BExp ~ T_KWD("then") ~ Block ~ T_KWD("else") ~ Block) ==>
-    { case (((((x,y),z),u),v),w) => If(y, u, w): Stmt } ||
-  (T_KWD("while") ~ BExp ~ T_KWD("do") ~ Block) ==> { case (((x, y), z), w) => While(y, w) } 
- 
-lazy val Stmts: Parser[List[Token], Block] =
-  (Stmt ~ T_SEMI ~ Stmts) ==> { case ((x, y), z) => x :: z : Block } ||
-  (Stmt ==> ((s) => List(s) : Block))
-
-lazy val Block: Parser[List[Token], Block] =
-  (T_BEGIN ~> Stmts <~ T_END) || 
-  (Stmt ==> ((s) => List(s)))
-
-
-// examples
-val p1 = "x := 5"
-val p1_toks = Tok.fromString(p1) 
-val p1_ast = Block.parse_all(p1_toks)
-println(p1_toks)
-println(p1_ast)
-
-val p1a = "{ x := 5; y := 8}"
-val p1a_toks = Tok.fromString(p1a) 
-val p1a_ast = Block.parse_all(p1a_toks)
-println(p1a_ast)
-
-val p2 = "5 = 6"
-val p2_toks = Tok.fromString(p2) 
-val p2_ast = BExp.parse_all(p2_toks)
-println(p2_ast)
-
-val p2a = "true"
-val p2a_toks = Tok.fromString(p2a) 
-val p2a_ast = BExp.parse_all(p2a_toks)
-println(p2a_ast)
-
-val p3 = "if true then skip else skip"
-val p3_toks = Tok.fromString(p3) 
-val p3_ast = Stmt.parse_all(p3_toks)
-println(p3_ast)
-
-val p3a = "if true then x := 5 else x := 10"
-val p3a_toks = Tok.fromString(p3a) 
-val p3a_ast = Stmt.parse_all(p3a_toks)
-println(p3a_ast)
-
-val p3b = "if false then x := 5 else x := 10"
-val p3b_toks = Tok.fromString(p3b) 
-val p3b_ast = Stmt.parse_all(p3b_toks)
-println(p3b_ast)
-
-// multiplication
-val p4 = """{ x := 5;
-              y := 4;
-              r := 0;
-              while y > 0 do {
-                 r := r + x;
-                 y := y - 1
-              } 
-            }"""
-val p4_toks = Tok.fromString(p4) 
-val p4_ast = Block.parse_all(p4_toks)
-println(p4_ast)
-
-val p5 = """
- n := 9;
- minus1 := 0;
- minus2 := 1;
- temp := 0;
- while n > 0 do  {
-   temp := minus2;
-   minus2 := minus1 + minus2;
-   minus1 := temp;
-   n := n - 1
- };
- fib_res := minus2
-"""
-val p5_toks = Tok.fromString(p5) 
-val p5_ast = Stmts.parse_all(p5_toks)
-
-// interpreter
-type Env = Map[String, Int]
-
-def eval_bexp(b: BExp, env: Env) : Boolean = b match {
-  case True => true
-  case False => false
-  case Bop("=", a1, a2) => eval_aexp(a1, env) == eval_aexp(a2, env)
-  case Bop("!=", a1, a2) => !(eval_aexp(a1, env) == eval_aexp(a2, env))
-  case Bop(">", a1, a2) => eval_aexp(a1, env) > eval_aexp(a2, env)
-  case Bop("<", a1, a2) => eval_aexp(a1, env) < eval_aexp(a2, env)
-}
-
-def eval_aexp(a: AExp, env : Env) : Int = a match {
-  case Num(i) => i
-  case Var(s) => env(s)
-  case Aop("+", a1, a2) => eval_aexp(a1, env) + eval_aexp(a2, env)
-  case Aop("-", a1, a2) => eval_aexp(a1, env) - eval_aexp(a2, env)
-  case Aop("*", a1, a2) => eval_aexp(a1, env) * eval_aexp(a2, env)
-}
-
-def eval_stmt(s: Stmt, env: Env) : Env = s match {
-  case Skip => env
-  case Assign(x, a) => env + (x -> eval_aexp(a, env))
-  case If(b, bl1, bl2) => if (eval_bexp(b, env)) eval_bl(bl1, env) else eval_bl(bl2, env) 
-  case While(b, bl) => 
-    if (eval_bexp(b, env)) eval_stmt(While(b, bl), eval_bl(bl, env))
-    else env
-}
-
-def eval_bl(bl: Block, env: Env) : Env = bl match {
-  case Nil => env
-  case s::bl => eval_bl(bl, eval_stmt(s, env))
-}
-
-//examples
-println(eval_stmt(p3a_ast.head, Map.empty))
-println(eval_stmt(p3b_ast.head, Map.empty))
-println(eval_bl(p4_ast.head, Map.empty))
-println(eval_bl(p5_ast.head, Map.empty))