--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/fun/fun_parser.scala Sat Jul 04 22:12:18 2020 +0100
@@ -0,0 +1,199 @@
+// A parser for the Fun language
+//================================
+//
+// call with
+//
+// scala fun_parser.scala fact.tks
+//
+// scala fun_parser.scala defs.tks
+//
+// this will generate a .prs file that can be deserialised back
+// into a list of declarations
+
+object Fun_Parser {
+
+import scala.language.implicitConversions
+import scala.language.reflectiveCalls
+import scala.util._
+import java.io._
+
+abstract class Token extends Serializable
+case object T_SEMI extends Token
+case object T_COMMA extends Token
+case object T_LPAREN extends Token
+case object T_RPAREN extends Token
+case class T_ID(s: String) extends Token
+case class T_OP(s: String) extends Token
+case class T_NUM(n: Int) extends Token
+case class T_KWD(s: String) extends Token
+
+
+// Parser combinators
+// type parameter I needs to be of Seq-type
+//
+abstract class Parser[I, T](implicit ev: I => Seq[_]) {
+ def parse(ts: I): Set[(T, I)]
+
+ def parse_single(ts: I) : T =
+ parse(ts).partition(_._2.isEmpty) match {
+ case (good, _) if !good.isEmpty => good.head._1
+ case (_, err) => {
+ println (s"Parse Error\n${err.minBy(_._2.length)}") ; sys.exit(-1) }
+ }
+}
+
+// convenience for writing grammar rules
+case class ~[+A, +B](_1: A, _2: B)
+
+class SeqParser[I, T, S](p: => Parser[I, T],
+ q: => Parser[I, S])(implicit ev: I => Seq[_]) 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, T](p: => Parser[I, T],
+ q: => Parser[I, T])(implicit ev: I => Seq[_]) extends Parser[I, T] {
+ def parse(sb: I) = p.parse(sb) ++ q.parse(sb)
+}
+
+class FunParser[I, T, S](p: => Parser[I, T],
+ f: T => S)(implicit ev: I => Seq[_]) extends Parser[I, S] {
+ def parse(sb: I) =
+ for ((head, tail) <- p.parse(sb)) yield (f(head), tail)
+}
+
+// convenient combinators
+implicit def ParserOps[I, T](p: Parser[I, T])(implicit ev: I => Seq[_]) = new {
+ def || (q : => Parser[I, T]) = new AltParser[I, T](p, q)
+ def ==>[S] (f: => T => S) = new FunParser[I, T, S](p, f)
+ def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q)
+}
+
+def ListParser[I, T, S](p: => Parser[I, T],
+ q: => Parser[I, S])(implicit ev: I => Seq[_]): Parser[I, List[T]] = {
+ (p ~ q ~ ListParser(p, q)) ==> { case x ~ _ ~ z => x :: z : List[T] } ||
+ (p ==> ((s) => List(s)))
+}
+
+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)
+
+implicit def TokOps(t: Token) = new {
+ def || (q : => Parser[List[Token], Token]) = new AltParser[List[Token], Token](t, q)
+ def ==>[S] (f: => Token => S) = new FunParser[List[Token], Token, S](t, f)
+ def ~[S](q : => Parser[List[Token], S]) = new SeqParser[List[Token], Token, S](t, q)
+}
+
+case object NumParser extends Parser[List[Token], Int] {
+ def parse(ts: List[Token]) = ts match {
+ case T_NUM(n)::ts => Set((n, 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 ()
+ }
+}
+
+
+
+// Abstract syntax trees for the Fun language
+abstract class Exp extends Serializable
+abstract class BExp extends Serializable
+abstract class Decl extends Serializable
+
+case class Def(name: String, args: List[String], body: Exp) extends Decl
+case class Main(e: Exp) extends Decl
+
+case class Call(name: String, args: List[Exp]) extends Exp
+case class If(a: BExp, e1: Exp, e2: Exp) extends Exp
+case class Write(e: Exp) extends Exp
+case class Var(s: String) extends Exp
+case class Num(i: Int) extends Exp
+case class Aop(o: String, a1: Exp, a2: Exp) extends Exp
+case class Sequence(e1: Exp, e2: Exp) extends Exp
+case class Bop(o: String, a1: Exp, a2: Exp) extends BExp
+
+
+
+// Grammar Rules for the Fun language
+
+// arithmetic expressions
+lazy val Exp: Parser[List[Token], Exp] =
+ (T_KWD("if") ~ BExp ~ T_KWD("then") ~ Exp ~ T_KWD("else") ~ Exp) ==>
+ { case _ ~ x ~ _ ~ y ~ _ ~ z => If(x, y, z): Exp } ||
+ (M ~ T_SEMI ~ Exp) ==> { case x ~ _ ~ y => Sequence(x, y): Exp } || M
+lazy val M: Parser[List[Token], Exp] =
+ (T_KWD("write") ~ L) ==> { case _ ~ y => Write(y): Exp } || L
+lazy val L: Parser[List[Token], Exp] =
+ (T ~ T_OP("+") ~ Exp) ==> { case x ~ _ ~ z => Aop("+", x, z): Exp } ||
+ (T ~ T_OP("-") ~ Exp) ==> { case x ~ _ ~ z => Aop("-", x, z): Exp } || T
+lazy val T: Parser[List[Token], Exp] =
+ (F ~ T_OP("*") ~ T) ==> { case x ~ _ ~ z => Aop("*", x, z): Exp } ||
+ (F ~ T_OP("/") ~ T) ==> { case x ~ _ ~ z => Aop("/", x, z): Exp } ||
+ (F ~ T_OP("%") ~ T) ==> { case x ~ _ ~ z => Aop("%", x, z): Exp } || F
+lazy val F: Parser[List[Token], Exp] =
+ (IdParser ~ T_LPAREN ~ ListParser(Exp, T_COMMA) ~ T_RPAREN) ==>
+ { case x ~ _ ~ z ~ _ => Call(x, z): Exp } ||
+ (T_LPAREN ~ Exp ~ T_RPAREN) ==> { case _ ~ y ~ _ => y: Exp } ||
+ IdParser ==> { case x => Var(x): Exp } ||
+ NumParser ==> { case x => Num(x): Exp }
+
+// boolean expressions
+lazy val BExp: Parser[List[Token], BExp] =
+ (Exp ~ T_OP("==") ~ Exp) ==> { case x ~ _ ~ z => Bop("==", x, z): BExp } ||
+ (Exp ~ T_OP("!=") ~ Exp) ==> { case x ~ _ ~ z => Bop("!=", x, z): BExp } ||
+ (Exp ~ T_OP("<") ~ Exp) ==> { case x ~ _ ~ z => Bop("<", x, z): BExp } ||
+ (Exp ~ T_OP(">") ~ Exp) ==> { case x ~ _ ~ z => Bop("<", z, x): BExp } ||
+ (Exp ~ T_OP("<=") ~ Exp) ==> { case x ~ _ ~ z => Bop("<=", x, z): BExp } ||
+ (Exp ~ T_OP("=>") ~ Exp) ==> { case x ~ _ ~ z => Bop("<=", z, x): BExp }
+
+lazy val Defn: Parser[List[Token], Decl] =
+ (T_KWD("def") ~ IdParser ~ T_LPAREN ~ ListParser(IdParser, T_COMMA) ~ T_RPAREN ~ T_OP("=") ~ Exp) ==>
+ { case _ ~ y ~ _ ~ w ~ _ ~ _ ~ r => Def(y, w, r): Decl }
+
+lazy val Prog: Parser[List[Token], List[Decl]] =
+ (Defn ~ T_SEMI ~ Prog) ==> { case x ~ _ ~ z => x :: z : List[Decl] } ||
+ (Exp ==> ((s) => List(Main(s)) : List[Decl]))
+
+
+
+// Reading tokens and Writing parse trees
+
+def serialise[T](fname: String, data: T) = {
+ import scala.util.Using
+ Using(new ObjectOutputStream(new FileOutputStream(fname))) {
+ out => out.writeObject(data)
+ }
+}
+
+def deserialise[T](fname: String) : Try[T] = {
+ import scala.util.Using
+ Using(new ObjectInputStream(new FileInputStream(fname))) {
+ in => in.readObject.asInstanceOf[T]
+ }
+}
+
+
+def main(args: Array[String]) : Unit= {
+ val fname = args(0)
+ val pname = fname.stripSuffix(".tks") ++ ".prs"
+ val tks = deserialise[List[Token]](fname).getOrElse(Nil)
+ serialise(pname, Prog.parse_single(tks))
+
+ // testing whether read-back is working
+ //val ptree = deserialise[List[Decl]](pname).get
+ //println(s"Reading back from ${pname}:\n${ptree.mkString("\n")}")
+}
+
+}