Control.Monad.Primitive

Class of monads which can perform primitive state-transformer actions.

RealWorld is deeply magical. It is primitive, but it is not unlifted (hence ptrArg). We never manipulate values of type RealWorld; it's only used in the type system, to parameterise State#.

Execute a primitive operation with no result.

Class of primitive monads for state-transformer actions.

Unlike PrimMonad, this typeclass requires that the Monad be fully expressed as a state transformer, therefore disallowing other monad transformers on top of the base IO or ST.

PrimMonad's state token type can be annoying to handle in constraints. This typeclass lets users (visually) notice PrimState equality constraints less, by witnessing that s ~ PrimState m.

PrimBase's state token type can be annoying to handle in constraints. This typeclass lets users (visually) notice PrimState equality constraints less, by witnessing that s ~ PrimState m.

Lifts a PrimBase into another PrimMonad with the same underlying state token type.

Convert a PrimBase to another monad with the same state token.

Convert a PrimBase with a RealWorld state token to IO

Convert a PrimBase to ST

Convert an IO action to a PrimMonad.

Convert an ST action to a PrimMonad.

Convert a PrimBase to another monad with a possibly different state token. This operation is highly unsafe!

Convert any PrimBase to IO. This operation is highly unsafe!

Convert any PrimBase to ST with an arbitrary state token. This operation is highly unsafe!

Convert an IO action to any PrimMonad. This operation is highly unsafe!

Convert an ST action with an arbitrary state token to any PrimMonad. This operation is highly unsafe!

See unsafeInlineIO. This function is not recommended for the same reasons.

Generally, do not use this function. It is the same as accursedUnutterablePerformIO from bytestring and is well behaved under narrow conditions. See the documentation of that function to get an idea of when this is sound. In most cases GHC.IO.Unsafe.unsafeDupablePerformIO should be preferred.

See unsafeInlineIO. This function is not recommended for the same reasons. Prefer runST when s is free.

Ensure that the value is considered alive by the garbage collection. Warning: GHC has optimization passes that can erase touch if it is certain that an exception is thrown afterward. Prefer keepAlive.

Variant of touch that keeps a value of an unlifted type (e.g. MutableByteArray#) alive.

Keep value x alive until computation k completes. Warning: This primop exists for completeness, but it is difficult to use correctly. Prefer keepAliveUnlifted if the value to keep alive is simply a wrapper around an unlifted type (e.g. ByteArray).

Variant of keepAlive in which the value kept alive is of an unlifted boxed type.

Create an action to force a value; generalizes evaluate