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Pure functional JDBC layer for Scala.

There is a newer version: 0.4.3

package doobie.free

import scalaz.{ Catchable, Free => F, Kleisli, Monad, ~>, \/ }
import scalaz.concurrent.Task

import doobie.util.capture._

object kleislitrans {

  /** 
   * Typeclass for algebras that have an instance of our default Kleisli interpreter. This allows us
   * to do arbitrary lifting rather than hard-coding each case.
   */
  trait KleisliTrans[Op[_]] { mod =>

    /** The carrier type for this interpreter; J for JDBC type. */
    type J

    /** Free monad over the free functor of `Op`. */
    type OpIO[A] = F[Op, A]

    /** 
     * Natural transformation from `Op` to `Kleisli` for the given `M`, consuming a `J`. 
     * @group Algebra
     */
    def interpK[M[_]: Monad: Catchable: Capture]: Op ~> Kleisli[M, J, ?]

    /** 
     * Natural transformation from `OpIO` to `Kleisli` for the given `M`, consuming a `J`. 
     * @group Algebra
     */
    def transK[M[_]: Monad: Catchable: Capture]: OpIO ~> Kleisli[M, J, ?] =
      new (OpIO ~> Kleisli[M, J, ?]) {
        def apply[A](ma: OpIO[A]): Kleisli[M, J, A] =
          ma.foldMap[Kleisli[M, J, ?]](interpK[M])
      }

    /** 
     * Natural transformation from `OpIO` to `M`, given a `J`. 
     * @group Algebra
     */
    def trans[M[_]: Monad: Catchable: Capture](c: J): OpIO ~> M =
     new (OpIO ~> M) {
       def apply[A](ma: OpIO[A]): M[A] = 
         transK[M].apply(ma).run(c)
     }

  }

  object KleisliTrans {
    type Aux[O[_], J0] = KleisliTrans[O] { type J = J0 }
  }

}