distributed-process- Cloud Haskell: Erlang-style concurrency in Haskell

Safe HaskellNone



Reimplementation of Dynamic that supports dynBind

We don't have access to the internal representation of Dynamic, otherwise we would not have to redefine it completely. Note that we use this only internally, so the incompatibility with our Dynamic from the standard Dynamic is not important.



fromDyn :: Typeable a => Dynamic -> a -> aSource

fromDynamic :: forall a. Typeable a => Dynamic -> Maybe aSource

dynBind :: TyCon -> (forall a b. m a -> (a -> m b) -> m b) -> Dynamic -> Dynamic -> Maybe DynamicSource

dynBind' :: TyCon -> (forall a b. m a -> (a -> m b) -> m b) -> Dynamic -> Dynamic -> DynamicSource

dynKleisli :: TyCon -> (forall a b c. (a -> m b) -> (b -> m c) -> a -> m c) -> Dynamic -> Dynamic -> Maybe DynamicSource

Dynamically typed Kleisli composition

unsafeCoerce# :: a -> b

The function unsafeCoerce# allows you to side-step the typechecker entirely. That is, it allows you to coerce any type into any other type. If you use this function, you had better get it right, otherwise segmentation faults await. It is generally used when you want to write a program that you know is well-typed, but where Haskell's type system is not expressive enough to prove that it is well typed.

The following uses of unsafeCoerce# are supposed to work (i.e. not lead to spurious compile-time or run-time crashes):

  • Casting any lifted type to Any
  • Casting Any back to the real type
  • Casting an unboxed type to another unboxed type of the same size (but not coercions between floating-point and integral types)
  • Casting between two types that have the same runtime representation. One case is when the two types differ only in "phantom" type parameters, for example Ptr Int to Ptr Float, or [Int] to [Float] when the list is known to be empty. Also, a newtype of a type T has the same representation at runtime as T.

Other uses of unsafeCoerce# are undefined. In particular, you should not use unsafeCoerce# to cast a T to an algebraic data type D, unless T is also an algebraic data type. For example, do not cast Int->Int to Bool, even if you later cast that Bool back to Int->Int before applying it. The reasons have to do with GHC's internal representation details (for the congnoscenti, data values can be entered but function closures cannot). If you want a safe type to cast things to, use Any, which is not an algebraic data type.