This package provides Haskell data serialisation independent of evaluation,
by accessing the Haskell heap using foreign primitive operations.
Any Haskell data structure apart from mutable data structures (
TVars) can be serialised and later deserialised during the same run,
or loaded into a new run, of the same program (the same executable file).
The library provides operations to
serialize Haskell heap data,
trySerializeWith :: a -> Int -> IO (Serialized a) -- Int is maximum buffer size to use trySerialize :: a -> IO (Serialized a) -- uses default (maximum) buffer size deserialize :: Serialized a -> IO a
The data type
Serialized a is an opaque representation of serialised
Haskell data (it contains a
A phantom type
a ensures type safety within the same program run.
a can be polymorphic (at compile time, that is) when
is not used apart from being argument to
When data are externalised (written to disk or communicated over the
network) using the provided instances of
a needs to be monomorphic because they require
The instances for
read . show == id.
Packman serialisation is orthogonal to evaluation, heap data are serialised in their current state of evaluation, they might be entirely unevaluated (a thunk) or only partially evaluated (containing thunks). Therefore, there can be cases where a mutable data structure is captured by a thunk, and lead to serialisation failures (typically related to lazy I/O).
The serialisation routine will throw a
PackException if an error occurs
inside the C code which accesses the Haskell heap, if a mutable data
structure is serialised, or if the serialised data is too large.
In presence of concurrent threads, another thread might be evaluating
data referred to by the data to be serialised. In this case, the calling
thread will block on the ongoing evaluation and continue when evaluated
data is available.
Internally, there is a
P_BLACKHOLE to signal the
condition, but it is hidden inside the core library