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Diffstat (limited to 'docs/examples/tcpoly/monads/Monads.scala')
-rw-r--r-- | docs/examples/tcpoly/monads/Monads.scala | 69 |
1 files changed, 0 insertions, 69 deletions
diff --git a/docs/examples/tcpoly/monads/Monads.scala b/docs/examples/tcpoly/monads/Monads.scala deleted file mode 100644 index b6e3d5b9a8..0000000000 --- a/docs/examples/tcpoly/monads/Monads.scala +++ /dev/null @@ -1,69 +0,0 @@ -package examples.tcpoly.monad; - -trait Monads { - /** - * class Monad m where - * (>>=) :: m a -> (a -> m b) -> m b - * return :: a -> m a - * - * MonadTC encodes the above Haskell type class, - * an instance of MonadTC corresponds to a method dictionary. - * (see http://lampwww.epfl.ch/~odersky/talks/wg2.8-boston06.pdf) - * - * Note that the identity (`this') of the method dictionary does not really correspond - * to the instance of m[x] (`self') that is `wrapped': e.g., unit does not use `self' (which - * corresponds to the argument of the implicit conversion that encodes an instance of this type class) - */ - // Option =:= [x] => Option[x] <: [x] => Any -// trait MonadTC[m <: [x] => Any, a] { - // MonadTC[m[x], a] x is a type parameter too -- should not write e.g., m[Int] here - trait MonadTC[m[x], a] { - def unit[a](orig: a): m[a] - - // >>='s first argument comes from the implicit definition constructing this "method dictionary" - def >>=[b](fun: a => m[b]): m[b] - } -} - -/** - * instance Monad Maybe where - * (Just x) >>= k = k x - * Nothing >>= _ = Nothing - */ -trait OptionMonad extends Monads { - // this implicit method encodes the Monad type class instance for Option - implicit def OptionInstOfMonad[a](self: Option[a]): MonadTC[Option, a] - = new MonadTC[Option, a] { - def unit[a](orig: a) = Some(orig) - def >>=[b](fun: a => Option[b]): Option[b] = self match { - case Some(x) => fun(x) - case None => None - } - } -} - -object main extends OptionMonad with Application { - Console.println(Some("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa") >>= (x => Some(x.length))) -} - - -/* -trait MonadTC[m[x], a] requires m[x] { - def unit[a](orig: a): m[a] - - // >>='s first argument comes from the implicit definition constructing this "method dictionary" - def >>=[b](fun: a => m[b]): m[b] -} - -abstract class OptionIsMonad[t[x] <: Option[x], a] implicit extends MonadTC[t, a] { - def unit[a](orig: a) = Some(orig) // TODO: problematic.. is a meta-member: not invoked on this -} - -class SomeIsMonad[a] extends OptionIsMonad[Some, a] { - def >>=[b](fun: a => Option[b]): Option[b] = fun(x) -} - -class NoneIsMonad[a] extends OptionIsMonad[None, a] { - def >>=[b](fun: a => Option[b]): Option[b] = None -} -*/ |