1 // CW3

     2 

     3 import $file.lexer

     4 import lexer._ 

     5 

     6 

     7 case class ~[+A, +B](_1: A, _2: B)

     8 type IsSeq[A] = A => Seq[_]

     9 

    10 abstract class Parser[I : IsSeq, T] {

    11   def parse(ts: I): Set[(T, I)]

    12 

    13   def parse_all(ts: I) : Set[T] =

    14     for ((head, tail) <- parse(ts); if tail.isEmpty) yield head

    15 }

    16 

    17 class SeqParser[I : IsSeq, T, S](p: => Parser[I, T], q: => Parser[I, S]) extends Parser[I, ~[T, S]] {

    18   def parse(sb: I) = 

    19     for ((head1, tail1) <- p.parse(sb); 

    20          (head2, tail2) <- q.parse(tail1)) yield (new ~(head1, head2), tail2)

    21 }

    22 

    23 class AltParser[I : IsSeq, T](p: => Parser[I, T], q: => Parser[I, T]) extends Parser[I, T] {

    24   def parse(sb: I) = p.parse(sb) ++ q.parse(sb)   

    25 }

    26 

    27 class FunParser[I : IsSeq, T, S](p: => Parser[I, T], f: T => S) extends Parser[I, S] {

    28   def parse(sb: I) = 

    29     for ((head, tail) <- p.parse(sb)) yield (f(head), tail)

    30 }

    31 

    32 // New parser that takes as input a list of tokens

    33 case class TokenListParser(ts: List[Token]) extends Parser[List[Token], List[Token]] {

    34     def parse(tsb: List[Token]) = {

    35         val (prefix, suffix) = tsb.splitAt(ts.length)

    36         if (prefix == ts) Set((prefix, suffix)) else Set()

    37     }

    38 }

    39 

    40 // Implicit definitions to go from a token 

    41 // or a list of tokens to a TokenListParser

    42 implicit def token2parser(t: Token) = TokenListParser(List(t))

    43 implicit def tokenList2parser(ts: List[Token]) = TokenListParser(ts)

    44 

    45 implicit def ParserOps[I : IsSeq, T](p: Parser[I, T]) = new {

    46   def || (q : => Parser[I, T]) = new AltParser[I, T](p, q)

    47   def ==>[S] (f: => T => S) = new FunParser[I, T, S](p, f)

    48   def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q)

    49 }

    50 

    51 implicit def TokenOps(t: Token) = new {

    52     def || (q : => Parser[List[Token], List[Token]]) = new AltParser[List[Token], List[Token]](List(t), q)

    53     def || (qs : List[Token]) = new AltParser[List[Token], List[Token]](List(t), qs)

    54     def ==>[S] (f: => List[Token] => S) = new FunParser[List[Token], List[Token], S](List(t), f)

    55     def ~[S](q : => Parser[List[Token], S]) =

    56         new SeqParser[List[Token], List[Token], S](List(t), q)

    57     def ~ (qs : List[Token]) =

    58         new SeqParser[List[Token], List[Token], List[Token]](List(t), qs)

    59 }

    60 

    61 implicit def TokenListOps(ts: List[Token]) = new {

    62     def || (q : => Parser[List[Token], List[Token]]) = new AltParser[List[Token], List[Token]](ts, q)

    63     def || (qs : List[Token]) = new AltParser[List[Token], List[Token]](ts, qs)

    64     def ==>[S] (f: => List[Token] => S) = new FunParser[List[Token], List[Token], S](ts, f)

    65     def ~[S](q : => Parser[List[Token], S]) =

    66         new SeqParser[List[Token], List[Token], S](ts, q)

    67     def ~ (qs : List[Token]) =

    68         new SeqParser[List[Token], List[Token], List[Token]](ts, qs)

    69 }

    70 

    71 // Abstract Syntax Trees

    72 abstract class Stmt

    73 abstract class AExp

    74 abstract class BExp

    75 

    76 type Block = List[Stmt]

    77 

    78 case object Skip extends Stmt

    79 case class If(a: BExp, bl1: Block, bl2: Block) extends Stmt

    80 case class While(b: BExp, bl: Block) extends Stmt

    81 case class Assign(s: String, a: AExp) extends Stmt

    82 case class Read(s: String) extends Stmt

    83 case class WriteId(s: String) extends Stmt  // for printing values of variables

    84 case class WriteString(s: String) extends Stmt  // for printing words

    85 case class For(counter: String, lower: AExp, upper: AExp, code: Block) extends Stmt

    86 

    87 

    88 case class Var(s: String) extends AExp

    89 case class Num(i: Int) extends AExp

    90 case class Aop(o: String, a1: AExp, a2: AExp) extends AExp

    91 

    92 case object True extends BExp

    93 case object False extends BExp

    94 case class Bop(o: String, a1: AExp, a2: AExp) extends BExp

    95 case class And(b1: BExp, b2: BExp) extends BExp

    96 case class Or(b1: BExp, b2: BExp) extends BExp

    97 

    98 case class IdParser() extends Parser[List[Token], String] {

    99     def parse(tsb: List[Token]) = tsb match {

   100         case T_ID(id) :: rest => Set((id, rest))

   101         case _ => Set()

   102     }

   103 }

   104 

   105 case class NumParser() extends Parser[List[Token], Int] {

   106     def parse(tsb: List[Token]) = tsb match {

   107         case T_NUM(n) :: rest => Set((n, rest))

   108         case _ => Set()

   109     }

   110 }

   111 

   112 case class StringParser() extends Parser[List[Token], String] {

   113     def parse(tsb: List[Token]) = tsb match {

   114         case T_STRING(s) :: rest => Set((s, rest))

   115         case _ => Set()

   116     }

   117 }

   118 

   119 // WHILE Language Parsing

   120 lazy val AExp: Parser[List[Token], AExp] = 

   121   (Te ~ T_OP("+") ~ AExp) ==> { case x ~ _ ~ z => Aop("+", x, z): AExp } ||

   122   (Te ~ T_OP("-") ~ AExp) ==> { case x ~ _ ~ z => Aop("-", x, z): AExp } || Te

   123 lazy val Te: Parser[List[Token], AExp] = 

   124   (Fa ~ T_OP("*") ~ Te) ==> { case x ~ _ ~ z => Aop("*", x, z): AExp } || 

   125   (Fa ~ T_OP("/") ~ Te) ==> { case x ~ _ ~ z => Aop("/", x, z): AExp } || 

   126   (Fa ~ T_OP("%") ~ Te) ==> { case x ~ _ ~ z => Aop("%", x, z): AExp } || Fa  

   127 lazy val Fa: Parser[List[Token], AExp] = 

   128    (T_PAREN("(") ~ AExp ~ T_PAREN(")")) ==> { case _ ~ y ~ _ => y } || 

   129    IdParser() ==> Var  || 

   130    NumParser() ==> Num

   131 

   132 lazy val BExp: Parser[List[Token], BExp] = 

   133    (AExp ~ T_OP("==") ~ AExp) ==> { case x ~ _ ~ z => Bop("==", x, z): BExp } || 

   134    (AExp ~ T_OP("!=") ~ AExp) ==> { case x ~ _ ~ z => Bop("!=", x, z): BExp } || 

   135    (AExp ~ T_OP("<") ~ AExp) ==> { case x ~ _ ~ z => Bop("<", x, z): BExp } || 

   136    (AExp ~ T_OP(">") ~ AExp) ==> { case x ~ _ ~ z => Bop(">", x, z): BExp } ||

   137    (T_PAREN("(") ~ BExp ~ List(T_PAREN(")"), T_OP("&&")) ~ BExp) ==> { case _ ~ y ~ _ ~ v => And(y, v): BExp } ||

   138    (T_PAREN("(") ~ BExp ~ List(T_PAREN(")"), T_OP("||")) ~ BExp) ==> { case _ ~ y ~ _ ~ v => Or(y, v): BExp } ||

   139    (T_KEYWORD("true") ==> (_ => True: BExp )) || 

   140    (T_KEYWORD("false") ==> (_ => False: BExp )) ||

   141    (T_PAREN("(") ~ BExp ~ T_PAREN(")")) ==> { case _ ~ x ~ _ => x }

   142 

   143 lazy val Stmt: Parser[List[Token], Stmt] =

   144     T_KEYWORD("skip") ==> (_ => Skip: Stmt) ||

   145     (IdParser() ~ T_OP(":=") ~ AExp) ==> { case id ~ _ ~ z => Assign(id, z): Stmt } ||

   146     (T_KEYWORD("if") ~ BExp ~ T_KEYWORD("then") ~ Block ~ T_KEYWORD("else") ~ Block) ==> { case _ ~ y ~ _ ~ u ~ _ ~ w => If(y, u, w): Stmt } ||

   147     (T_KEYWORD("while") ~ BExp ~ T_KEYWORD("do") ~ Block) ==> { case _ ~ y ~ _ ~ w => While(y, w) : Stmt } ||

   148     (T_KEYWORD("read") ~ IdParser()) ==> { case _ ~ id => Read(id): Stmt} ||

   149     (T_KEYWORD("write") ~ IdParser()) ==> { case _ ~ id => WriteId(id): Stmt} ||

   150     (T_KEYWORD("write") ~ StringParser()) ==> { case _ ~ s => WriteString(s): Stmt} ||

   151     (T_KEYWORD("for") ~ IdParser() ~ T_OP(":=") ~ AExp ~ T_KEYWORD("upto") ~ AExp ~ T_KEYWORD("do") ~ Block) ==> {

   152       case _ ~ id ~ _ ~ lower ~ _ ~ upper ~ _ ~ blck => For(id, lower, upper, blck): Stmt

   153     }

   154 

   155 lazy val Stmts: Parser[List[Token], Block] =

   156     (Stmt ~ T_SEMI ~ Stmts) ==> { case x ~ _ ~ z => x :: z : Block } ||

   157     (Stmt ==> (s => List(s) : Block))

   158 

   159 lazy val Block: Parser[List[Token], Block] =

   160     (T_PAREN("{") ~ Stmts ~ T_PAREN("}")) ==> { case x ~ y ~ z => y} ||

   161     (Stmt ==> (s => List(s)))

   162