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Re: [scala] implementation hiding

by nuttycom :: Rate this Message:

This does not hide the type of MSequitor, but:

trait MBrace[C[X] <: MBrace[C,X],A] {
def nest( a : A ) : C[A]
def flatten[T <: C[C[A]]]( bsq : T ) : C[A]
}

// a monad that is a Seq
trait MBraceSeq[C[X] <: MBrace[C,X] with Seq[X],A] extends MBrace[C,A]

trait MSequitor[A] extends Seq[A] with MBrace[MSequitor,A]

object MBraceSequitor {
// one of the simplest witnesses of monad i can find
private case class MSequitorImpl[A]( a_ : A* ) extends MSequitor[A] {
override def nest( a : A ) = new MSequitorImpl[A]( a )
override def flatten[T <: MSequitor[MSequitor[A]]]( bsq : T ) :
MSequitor[A] = {
(new MSequitorImpl[A]( ) /: bsq)( {
( acc : MSequitor[A], e : MSequitor[A] ) => new
MSequitorImpl[A]( acc ++ e : _* )
} )
}
override def length = a_.length
override def elements = a_.elements
override def apply( n : Int ) = a_.apply( n )
}
}

// a statement of the instance relation
class MBraceSequitor[A] extends MBraceSeq[MSequitor,A] {
import MBraceSequitor._
val empty : MSequitor[A] = new MSequitorImpl[A]( )
override def nest( a : A ) = empty.nest( a )
override def flatten[T <: MSequitor[MSequitor[A]]]( bsq : T )
: MSequitor[A] = empty.flatten( bsq )
}

Kris

On Fri, Jun 26, 2009 at 12:47 PM, Meredith
Gregory<lgreg.meredith@...> wrote:

> All,
>
> Am i being stupid or is it impossible in the code below to construct a
> natural way to hide the concrete case class?
>
> Best wishes,
>
> --greg
>
> trait MBrace[C[X] <: MBrace[C,X],A] {
> def nest( a : A ) : C[A]
> def flatten[T <: C[C[A]]]( bsq : T ) : C[A]
> }
>
> // a monad that is a Seq
> trait MBraceSeq[C[X] <: MBrace[C,X] with Seq[X],A] extends MBrace[C,A]
>
> // one of the simplest witnesses of monad i can find
> case class MSequitor[A]( a_ : A* ) extends Seq[A] with MBrace[MSequitor,A] {
> override def nest( a : A ) = new MSequitor[A]( a )
> override def flatten[T <: MSequitor[MSequitor[A]]]( bsq : T ) :
> MSequitor[A] = {
>     (new MSequitor[A]( ) /: bsq)( {
>       ( acc : MSequitor[A], e : MSequitor[A] ) => ( acc ++ e
> ).asInstanceOf[MSequitor[A]]
>     } )
> }
> override def length = a_.length
> override def elements = a_.elements
> override def apply( n : Int ) = a_.apply( n )
> }
>
> // a statement of the instance relation
> class MBraceSequitor[A] extends MBraceSeq[MSequitor,A] {
> val empty : MSequitor[A] = new MSequitor[A]( )
> override def nest( a : A ) = empty.nest( a )
> override def flatten[T <: MSequitor[MSequitor[A]]]( bsq : T )
> : MSequitor[A] = empty.flatten( bsq )
> }
>
> --
> L.G. Meredith
> Managing Partner
> Biosimilarity LLC
> 1219 NW 83rd St
> Seattle, WA 98117
>
> +1 206.650.3740
>
> http://biosimilarity.blogspot.com
>

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