pathtype- Type-safe replacement for System.FilePath etc

Safe HaskellSafe



This module provides type-safe access to filepath manipulations.

It is designed to be imported instead of System.FilePath. (It is intended to provide versions of functions from that module which have equivalent functionality but are more typesafe). System.Path.Directory is a companion module providing a type-safe alternative to System.Directory.

The heart of this module is the Path ar fd abstract type which represents file and directory paths. The idea is that there are two phantom type parameters - the first should be Abs or Rel, and the second File or Dir. A number of type synonyms are provided for common types:

type AbsFile     = Path Abs File
type RelFile     = Path Rel File
type AbsDir      = Path Abs Dir
type RelDir      = Path Rel Dir

type AbsPath  fd = Path Abs fd
type RelPath  fd = Path Rel fd
type FilePath ar = Path ar File
type DirPath  ar = Path ar Dir

The type of the combine (aka </>) function gives the idea:

(</>) :: DirPath ar -> RelPath fd -> Path ar fd

Together this enables us to give more meaningful types to a lot of the functions, and (hopefully) catch a bunch more errors at compile time.

Overloaded string literals are supported, so with the OverloadedStrings extension enabled, you can:

f :: FilePath ar
f = "tmp" </> "someFile" <.> "ext"

If you don't want to use OverloadedStrings, you can use the construction fns:

f :: FilePath ar
f = asDirPath "tmp" </> asFilePath "someFile" <.> "ext"


f :: FilePath ar
f = asPath "tmp" </> asPath "someFile" <.> "ext"

or just...

f :: FilePath ar
f = asPath "tmp/someFile.ext"

One point to note is that whether one of these is interpreted as an absolute or a relative path depends on the type at which it is used:

*System.Path> f :: AbsFile
*System.Path> f :: RelFile

You will typically want to import as follows:

import Prelude hiding (FilePath)
import System.Path
import System.Path.Directory
import System.Path.IO

The basic API (and properties satisfied) are heavily influenced by Neil Mitchell's System.FilePath module.

Ben Moseley - (c) 2009-2010