pathtype-0.7.0.1: pathtype.cabal
Name: pathtype
Version: 0.7.0.1
Synopsis: Type-safe replacement for System.FilePath etc
Description:
This package provides type-safe access to filepath manipulations.
.
"System.Path" is designed to be used 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 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.
.
You can use the construction functions as follows:
.
> f :: Path.RelFile
> f = relDir "tmp" </> relFile "someFile" <.> "ext"
.
or...
.
> f :: Path.RelFile
> f = dirPath "tmp" </> filePath "someFile" <.> "ext"
.
or...
.
> f :: Path.RelFile
> f = path "tmp" </> path "someFile" <.> "ext"
.
or just...
.
> f :: Path.RelFile
> f = relFile "tmp/someFile.ext"
.
The first and the last implementations force the most specific types
and thus should be prefered.
.
Overloaded string literals are no longer supported,
since this extension is intended for alternative text storage types.
It would also decrease the type safety
if you could omit the path type and let the compiler guess its type.
.
You will typically want to import as follows:
.
> import qualified System.Path.Directory as Dir
> import qualified System.Path.IO as PathIO
> import qualified System.Path as Path
> import System.Path ((</>))
.
"System.Path.Generic" provides all functions with the OS as type parameter.
"System.Path.Posix" and "System.Path.Windows"
offers only path constructors and destructors
fixed to the corresponding operating system.
"System.Path" exports either "System.Path.Posix" or "System.Path.Windows"
depending on the host system
and additionally the manipulation functions from "System.Path.Generic".
This mix should be appropriate for the average use
and should free the user from writing type annotations.
.
The basic API (and properties satisfied) are heavily influenced
by Neil Mitchell's "System.FilePath" module.
.
.
Some notes on how to choose proper type parameters:
.
The @ar@ and the @fd@ type parameters have quite different meaning.
The types @Abs@ and @Rel@ refer to a property of the path,
whereas the type @File@ and @Dir@ refers to a property of a disk object.
You can decide whether a path is absolute or relative
by just watching (the beginning of) the path string.
In contrast to that, you have to access the disk
in order to check the existence and type of an disk object.
Even more, the disk object might change at any time,
e.g. the user might delete a file and create a directory of the same name,
or the disk object might not exist,
and the purpose of the path is to create an according file or directory.
That's why even if you have a path of type @FilePath ar@,
every function accessing the file must check
that the refered object exists and is a file.
Conversely, there is not much sense in checking the disk object type
and then chosing the path accordingly.
Instead, you must choose the path type according
to what type of disk object your application needs.
The reality check must be performed
and is performed by the standard functions
for every access to the object.
If an disk object is not of the type required by the path type
then this is a runtime exception that must be handled at runtime
but it is not a programming error.
.
Sometimes you have to change the type of a path
as an intermediate step to construct a path for an object of different type.
E.g. you may convert the path \"pkg\" from @DirPath@ to @FilePath@
because in the next step you like to extend it to \"pkg.tar.gz\".
This is valid use of the @Path@ type.
E.g. the function @dropExtensions@
reduces the @FilePath@ \"pkg.tar.gz\" to the new @FilePath@ \"pkg\"
although no-one expects that there is or will be a file with name \"pkg\".
Thus, if a function has a @FilePath@ parameter
then there is no warranty that it accesses the according file
and does not touch related disk objects.
It may well be that the function derives other file and directory names
from the path and accesses them.
That is, a @FilePath@ or @DirPath@ parameter
is mainly for documentation purposes
but it cannot prevent you seriously from any damage.
.
How to cope with user input?
You may get a path from the user, e.g. as command-line argument.
It might be either absolute or relative
and it might refer to an actual file or directory or
to something yet non-existing.
In most cases it will not be important
whether the path is absolute or relative,
thus you should choose the @AbsOrRel@ type parameter.
If somewhere in the program an @Abs@ path is needed
then you can assert that the path is actually absolutized somewhere
e.g. by @dynamicMakeAbsolute@.
If you prevent usage of @genericMakeAbsolute@
then you avoid to absolutize a path that is already absolutized.
.
The choice of the @fd@ type parameter follows a different reasoning:
Often you have a clear idea of
whether the user must pass a file or directory path.
The rule is: Just give the path the type you expect
but do not perform any checking
(unless you want to warn the user earlier about imminent danger).
The disk object type must checked for every access to the object, anyway,
so there is no point in checking it immediately.
With your choice of the @fd@ parameter
you just document its intended use.
.
It might be that the path is only a base name
used to construct other directory and file names.
E.g. for an Audacity project named @music@
you have to create the directory @music_data@ and the file @music.aup@.
In this case we recommend to give @music@ the type @FilePath@.
This type warrants that there is at least one final path component
in contrast to a directory path that might be empty.
You can easily convert a file path to a directory path
using @Path.dirFromFile@.
The reverse conversion is partial.
.
.
Some notes on file system links:
.
This package does not explicitly handle file system links.
We treat a file path containing links like any other file path.
The same holds for directory paths.
A link is handled like any other path component.
.
.
Some notes on drive-relative paths on Windows:
.
We use the @Rel@ type for paths that can be relative to any directory.
We use the @Abs@ type for all other paths,
i.e. for paths with explicit locations or
with restrictions on the set of locations.
Windows has a notion of drives and
maintains a current directory for every drive.
E.g. the path @\"c:text.txt\"@ refers to the current directory of drive @C@.
Since it cannot be freely combined with other directories
we treat this path like an absolute path.
This is consistent with the behaviour of the @filepath@ package.
E.g. @filepath@ evaluates all of the expressions
@\"\\\\abs\" \<\/\> \"c:driverel\"@, @\"c:\\\\abs\" \<\/\> \"c:driverel\"@,
@\"d:\\\\abs\" \<\/\> \"c:driverel\"@ to @\"c:driverel\"@.
In our package you would have to use @genericMakeAbsolute@
but we recommend to avoid its use.
.
Related packages:
.
* @path@: Provides a wrapper type around 'FilePath'
and maps to functions from @filepath@ package.
This warrants consistency with @filepath@ functions.
Requires Template Haskell.
.
* @data-filepath@:
Requires 'Typeable' and Template Haskell.
Stability: experimental
License: BSD3
Category: System
License-file: LICENSE
Author: Ben Moseley, Ben Millwood, Henning Thielemann
Maintainer: haskell@henning-thielemann.de, ben@moseley.name
HomePage: http://hub.darcs.net/thielema/pathtype/
Build-Type: Simple
Cabal-Version: >=1.8
Extra-Source-Files:
CHANGELOG
test/TestTemplate.hs
posix/System/Path/Host.hs
windows/System/Path/Host.hs
directory/pre-1.2/System/Path/ModificationTime.hs
directory/post-incl-1.2/System/Path/ModificationTime.hs
Source-Repository head
Type: darcs
Location: http://hub.darcs.net/thielema/pathtype/
Source-Repository this
Tag: 0.7.0.1
Type: darcs
Location: http://hub.darcs.net/thielema/pathtype/
Flag old-time
Description: Build with directory < 1.2 and old-time
Default: True
Flag buildTools
Description: Build tool for updating test module
Default: True
Library
Build-Depends:
utility-ht >=0.0.11 && <0.1,
QuickCheck >= 2.1.0.1 && < 3,
deepseq >= 1.3 && <1.5,
time >= 1.0 && < 2,
transformers >=0.3 && <0.5,
tagged >=0.7 && <0.9,
base >= 4 && < 5
If flag(old-time)
Build-Depends: directory >= 1 && < 1.2, old-time >= 1.0 && < 2
Hs-Source-Dirs: directory/pre-1.2
Else
Build-Depends: directory >= 1.2 && < 2
Hs-Source-Dirs: directory/post-incl-1.2
Hs-Source-Dirs: src
If os(windows)
Hs-Source-Dirs: windows
Else
Hs-Source-Dirs: posix
Exposed-Modules:
System.Path
System.Path.Generic
System.Path.Directory
System.Path.IO
System.Path.Posix
System.Path.Windows
Other-Modules:
System.Path.Host
System.Path.Internal
System.Path.RegularExpression
System.Path.ModificationTime
GHC-Options: -Wall -fwarn-tabs -fwarn-incomplete-record-updates -fwarn-unused-do-bind
Test-Suite test
Type: exitcode-stdio-1.0
Main-Is: Test.hs
Other-Modules: TestResult
Hs-Source-Dirs: test
Build-Depends:
pathtype,
random >=1.0 && <1.2,
base
GHC-Options: -Wall -fwarn-tabs -fwarn-incomplete-record-updates -fwarn-unused-do-bind
Executable create-pathtype-test
If flag(buildTools)
Build-Depends:
utility-ht >=0.0.12 && <0.1,
base
Else
Buildable: False
Main-Is: CreateTest.hs
Hs-Source-Dirs: tool
GHC-Options: -Wall -fwarn-tabs -fwarn-incomplete-record-updates -fwarn-unused-do-bind