| Safe Haskell | Trustworthy |
|---|---|
| Language | Haskell98 |
Data.Columbia.Utils
Description
Some utility functions. The reader strategies maintain the invariant that the stream is seeked to the beginning of a data entity, so that it is safe to use 'readData'/'writeData'/'seekTo' etc. The writer strategies maintain the invariant that the writer is seeked at the word that should receive the address of the data entity that is written. This allows the writer to write eagerly the address and so be tail recursive in some cases.
Think of a columbia file as just a transactional log that is continually being written to; transactions are able to reference other transactions by address, thus constructing data structures; a single address, called the root node address, at the beginning of the file determines the file's nominal mutable state. To keep the file from getting too large, it is garbage collected periodically; calls to the collector have to be programmed to happen manually at a time convenient for your application.
Please be aware that while you *can* write new addresses over old in the file, this is not compatible with the locking scheme, which is predicated on the assumption that all writing happens to the root block address and appending to the end of the file; in other words it is predicated on all data being immutable except the root block address. In order to do that, you will have to use your own locking scheme to make that work.
- rwProxy :: Proxy (PairCtx RWCtx NoCtx)
- readFileWrapper :: (MonadError e m, MonadIO m) => FilePath -> ReaderT (SeekableStream m Word8) m t -> m t
- writeFileWrapper :: (MonadError e m, MonadIO m) => FilePath -> ReaderT (SeekableWriter m Word8) m t -> m t
- nFields :: Monad m => (Word8, ConIndex, Int) -> ReaderT * (SeekableStream m Word8) m Int
Documentation
readFileWrapper :: (MonadError e m, MonadIO m) => FilePath -> ReaderT (SeekableStream m Word8) m t -> m t Source #
Opens a file for reading, under appropriate locks; seeks to the beginning of the data; runs the procedure. For common use, set m := IO.
writeFileWrapper :: (MonadError e m, MonadIO m) => FilePath -> ReaderT (SeekableWriter m Word8) m t -> m t Source #
Opens a file for writing, under appropriate locks; seeks to the beginning of the data; runs the procedure; accepts from the procedure an address to write as the new root node address.