This package offers small filesystem effects for polysemy, such as:
data FSExist m a where DoesFileExist :: Path b File -> FSExist m Bool DoesDirExist :: Path b Dir -> FSExist m Bool
It should be noted that these are very weak semantic abstractions, as it does
not provide a way to speak to the filesystem as a whole, and therefore is
somewhat unsuitable for mocking. These effects exist primarily to give
interpreters a way to be precise in the type of filesystem operations they use,
and should be treated in the same way as
Embed IO in that regard. However, if
you need a quick fix - then using this directly in application code is a slight
improvement over using
Embed IO directly.
Using these as very low level compilation units allows you to inject debugging everywhere you use a filesystem operation. For example, using co-log-polysemy we can do this:
data FileExists where FileExists :: Path b File -> FileExists FileNotExists :: Path b File -> FileExists data DirExists where DirExists :: Path b Dir -> DirExists DirNotExists :: Path b Dir -> DirExists logFileExists :: Members '[FSExist, Log FileExists] r => Sem r a -> Sem r a logFileExists = intercept \case DoesFileExist x -> do z <- doesFileExist x case z of True -> log $ FileExists x False -> log $ FileNotExists x return z DoesDirExist x -> doesDirExist x logDirExists :: Members '[FSExist, Log DirExists] r => Sem r a -> Sem r a logDirExists = intercept \case DoesDirExist x -> do z <- doesDirExist x case z of True -> log $ DirExists x False -> log $ DirNotExists x return z DoesFileExist x -> doesFileExist x
For a look at a unified version of filesystem operations, check out polysemy-fskvstore
Changelog for polysemy-fs
- Small filesystem effects for polysemy.