CODEWITHSUNDEEP
scalaparsing
David
David

Reputation: 165

scala parse wont return correct result

I am working on scala and I am trying to make this parser:

<expr> ::= <num>
     | (cond (<expr> <expr>) ...) # multi-armed conditional
     | (cond (<expr> <expr>) ... (else <expr>)) # multi-armed conditional w/ else

this is my code for this part:

  case SList(List(SSym(cond),SList(List(a,b)))) => CondExt(parse(SList(List.apply(a,b))))

when I run this code I get this error:

Status: CompilationFailure
solution.scala:53: error: type mismatch;
 found   : ExprExt
 required: List[(ExprExt, ExprExt)]
      case SList(List(SSym(cond),SList(List(a,b)))) => CondExt(parse(SList(List.apply(a,b))))

How is this error fixed I tried several other different ways:

  case SList(List(SSym(cond),SList(List((a,b)),SList(List((c,d)))))) =>  CondExt(SList(List(parse(a),parse(b))))

and for this I get this error:
Status: CompilationFailure
solution.scala:54: error: wrong number of arguments for <none>: (list: List[Library.SExpr])Library.SList
      case SList(List(SSym(cond),SList(List((a,b)),SList(List((c,d)))))) =>  CondExt(SList(List(parse(a),parse(b))))
                                      ^
solution.scala:54: error: not found: value a
      case SList(List(SSym(cond),SList(List((a,b)),SList(List((c,d)))))) =>  CondExt(SList(List(parse(a),parse(b))))

How can someone point me to my mistake that I am doing.

Extra Info:

case class CondExt(cs: List[(ExprExt, ExprExt)]) extends ExprExt
case class CondEExt(cs: List[(ExprExt, ExprExt)], e: ExprExt) extends ExprExt

sealed abstract class SExpr
case class SNum(n : Int) extends SExpr
case class SSym(s : String) extends SExpr
case class SList(l  : List[SExpr]) extends SExpr


object Parser {
  def parse(str: String): ExprExt = parse(Reader.read(str))

  def parse(sexpr: SExpr): ExprExt = {
  }
}

Upvotes: 1

Views: 542

Answers (1)

resueman
resueman

Reputation: 10623

The problem is here:

CondExt(parse(SList(List.apply(a,b))))

The parse(SList(...)) calls parse(arg:SExpr):ExprExt. This tries to call CondExt(arg:ExprExt), But CondExt only has an apply method defined for an argument of type List[(ExprExt, ExprExt)].

You either need to make CondExt take ExprExts, make parse return a List[(ExprExt, ExprExt)], or do something else to make the types match.

Upvotes: 1

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