diff -r 8f85d1f61663 -r 898c25a4e399 while1.scala --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/while1.scala Fri Nov 23 21:21:27 2012 +0000 @@ -0,0 +1,174 @@ +// A parser and evaluator for teh while language +// +//:load matcher.scala +//:load parser3.scala + +// 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", "print") +val SEMI: Rexp = ";" +val OP: Rexp = ALTS(":=", "=", "-", "+", "*", "!", "<", ">") +val WHITESPACE = PLUS(RANGE(" \n")) +val RPAREN: Rexp = ")" +val LPAREN: Rexp = "(" +val BEGIN: Rexp = "{" +val END: Rexp = "}" +val COMMENT = SEQS("/*", NOT(SEQS(STAR(ALLC), "*/", STAR(ALLC))), "*/") + +// tokens for classifying the strings that have been recognised +abstract class Token +case object T_WHITESPACE extends Token +case object T_COMMENT 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[Rule[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), + (COMMENT, (s) => T_COMMENT)) + +// the tokenizer +val Tok = Tokenizer(lexing_rules, List(T_WHITESPACE, T_COMMENT)) + +// 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 Print(s: String) 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) } || + (T_KWD("print") ~ IdParser) ==> { case (x, y) => Print(y) } + +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))) + +// 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 + case Print(x) => { println(env(x)); env } +} + +def eval_bl(bl: Block, env: Env) : Env = bl match { + case Nil => env + case s::bl => eval_bl(bl, eval_stmt(s, env)) +} + +def eval_prog(name: String) : Env = { + val tks = Tok.fromFile(name) + val ast = Stmts.parse_all(tks).head + eval_bl(ast, Map.empty) +} + + +//examples + +eval_prog("fib.while")