diff -r c7bdd7eac4cb -r 022e2cb1668d progs/c.scala --- a/progs/c.scala Sat Jul 04 16:58:12 2020 +0100 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,253 +0,0 @@ -// A parser and interpreter for the While language -// - -import scala.language.implicitConversions -import scala.language.reflectiveCalls -import scala.collection.immutable._ - -// more convenience for the semantic actions later on -case class ~[+A, +B](_1: A, _2: B) - - -type IsSeq[A] = A => Seq[_] - -abstract class Parser[I : IsSeq, T] { - def parse(ts: I): Set[(T, I)] - - def parse_all(ts: I) : Set[T] = - for ((head, tail) <- parse(ts); if tail.isEmpty) yield head -} - - - - -class SeqParser[I : IsSeq, T, S](p: => Parser[I, T], q: => Parser[I, S]) extends Parser[I, ~[T, S]] { - def parse(sb: I) = - for ((head1, tail1) <- p.parse(sb); - (head2, tail2) <- q.parse(tail1)) yield (new ~(head1, head2), tail2) -} - -class AltParser[I : IsSeq, T](p: => Parser[I, T], q: => Parser[I, T]) extends Parser[I, T] { - def parse(sb: I) = p.parse(sb) ++ q.parse(sb) -} - -class MapParser[I : IsSeq, T, S](p: => Parser[I, T], f: T => S) extends Parser[I, S] { - def parse(sb: I) = - for ((head, tail) <- p.parse(sb)) yield (f(head), tail) -} - -case class StrParser(s: String) extends Parser[String, String] { - def parse(sb: String) = { - val (prefix, suffix) = sb.splitAt(s.length) - if (prefix == s) Set((prefix, suffix)) else Set() - } -} - -case object NumParser extends Parser[String, Int] { - val reg = "[0-9]+".r - def parse(sb: String) = reg.findPrefixOf(sb) match { - case None => Set() - case Some(s) => { - val (head, tail) = sb.splitAt(s.length) - Set((head.toInt, tail)) - } - } -} - - -implicit def parser_interpolation(sc: StringContext) = new { - def p(args: Any*) = StrParser(sc.s(args:_*)) -} - -// this string interpolation allows us to write -// things like the following for a StrParser -// -// p"<_some_string_>" -// -// instead of StrParser(<_some_string_>) - - -implicit def ParserOps[I : IsSeq, T](p: Parser[I, T]) = new { - def ||(q : => Parser[I, T]) = new AltParser[I, T](p, q) - def ~[S](q : => Parser[I, S]) = new SeqParser[I, T, S](p, q) - def map[S](f: => T => S) = new MapParser[I, T, S](p, f) -} - -// these implicits allow us to use infic notation for -// sequences and alternatives; we also can write map -// for a parser - - -// the abstract syntax trees for the WHILE language -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 Write(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 -case class And(b1: BExp, b2: BExp) extends BExp -case class Or(b1: BExp, b2: BExp) extends BExp - -case object IdParser extends Parser[String, String] { - val reg = "[a-z][a-z,0-9]*".r - def parse(sb: String) = reg.findPrefixOf(sb) match { - case None => Set() - case Some(s) => Set(sb.splitAt(s.length)) - } -} - -// arithmetic expressions -lazy val AExp: Parser[String, AExp] = - (Te ~ p"+" ~ AExp).map[AExp]{ case x ~ _ ~ z => Aop("+", x, z) } || - (Te ~ p"-" ~ AExp).map[AExp]{ case x ~ _ ~ z => Aop("-", x, z) } || Te -lazy val Te: Parser[String, AExp] = - (Fa ~ p"*" ~ Te).map[AExp]{ case x ~ _ ~ z => Aop("*", x, z) } || - (Fa ~ p"/" ~ Te).map[AExp]{ case x ~ _ ~ z => Aop("/", x, z) } || Fa -lazy val Fa: Parser[String, AExp] = - (p"(" ~ AExp ~ p")").map{ case _ ~ y ~ _ => y } || - IdParser.map(Var) || - NumParser.map(Num) - -// boolean expressions with some simple nesting -lazy val BExp: Parser[String, BExp] = - (AExp ~ p"==" ~ AExp).map { case x ~ _ ~ z => Bop("==", x, z): BExp } || - (AExp ~ p"!=" ~ AExp).map { case x ~ _ ~ z => Bop("!=", x, z): BExp } || - (AExp ~ p"<" ~ AExp).map { case x ~ _ ~ z => Bop("<", x, z): BExp } || - (AExp ~ p">" ~ AExp).map { case x ~ _ ~ z => Bop(">", x, z): BExp } || - (p"(" ~ BExp ~ p")" ~ p"&&" ~ BExp).map { case _ ~ y ~ _ ~ _ ~ v => And(y, v): BExp } || - (p"(" ~ BExp ~ p")" ~ p"||" ~ BExp).map { case _ ~ y ~ _ ~ _ ~ v => Or(y, v): BExp } || - (p"true".map { _ => True: BExp }) || - (p"false".map { _ => False: BExp }) || - (p"(" ~ BExp ~ p")").map { case _ ~ x ~ _ => x } - -// statement / statements -lazy val Stmt: Parser[String, Stmt] = - ((p"skip".map {_ => Skip: Stmt}) || - (IdParser ~ p":=" ~ AExp).map { case x ~ _ ~ z => Assign(x, z): Stmt } || - (p"write(" ~ IdParser ~ p")").map { case _ ~ y ~ _ => Write(y): Stmt } || - (p"if" ~ BExp ~ p"then" ~ Block ~ p"else" ~ Block) - .map{ case _ ~ y ~ _ ~ u ~ _ ~ w => If(y, u, w): Stmt } || - (p"while" ~ BExp ~ p"do" ~ Block).map { case _ ~ y ~ _ ~ w => While(y, w) }) - -lazy val Stmts: Parser[String, Block] = - (Stmt ~ p";" ~ Stmts).map { case x ~ _ ~ z => x :: z : Block } || - (Stmt.map { s => List(s) : Block}) - -// blocks (enclosed in curly braces) -lazy val Block: Parser[String, Block] = - ((p"{" ~ Stmts ~ p"}").map{ case _ ~ y ~ _ => y } || - (Stmt.map(s => List(s)))) - - -Stmts.parse_all("x2:=5+3;") -Block.parse_all("{x:=5;y:=8}") -Block.parse_all("if(false)then{x:=5}else{x:=10}") - -val fib = """n := 10; - minus1 := 0; - minus2 := 1; - temp := 0; - while (n > 0) do { - temp := minus2; - minus2 := minus1 + minus2; - minus1 := temp; - n := n - 1 - }; - result := minus2""".replaceAll("\\s+", "") - -Stmts.parse_all(fib) - - -// an interpreter for the WHILE language -type Env = Map[String, Int] - -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) - case Aop("/", a1, a2) => eval_aexp(a1, env) / eval_aexp(a2, env) -} - -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) - case And(b1, b2) => eval_bexp(b1, env) && eval_bexp(b2, env) - case Or(b1, b2) => eval_bexp(b1, env) || eval_bexp(b2, 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 Write(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(bl: Block) : Env = eval_bl(bl, Map()) - -// parse + evaluate fib program; then lookup what is -// stored under the variable result -println(eval(Stmts.parse_all(fib).head)("result")) - - -// more examles - -// calculate and print all factors bigger -// than 1 and smaller than n -println("Factors") - -val factors = - """n := 12; - f := 2; - while (f < n / 2 + 1) do { - if ((n / f) * f == n) then { write(f) } else { skip }; - f := f + 1 - }""".replaceAll("\\s+", "") - -eval(Stmts.parse_all(factors).head) - -// calculate all prime numbers up to a number -println("Primes") - -val primes = - """end := 100; - n := 2; - while (n < end) do { - f := 2; - tmp := 0; - while ((f < n / 2 + 1) && (tmp == 0)) do { - if ((n / f) * f == n) then { tmp := 1 } else { skip }; - f := f + 1 - }; - if (tmp == 0) then { write(n) } else { skip }; - n := n + 1 - }""".replaceAll("\\s+", "") - -eval(Stmts.parse_all(primes).head)