Add function with_wd

Author: tarleb

README.md

@@ -213,7 +213,6 @@ Returns:
 
 -   The result(s) of the call to `callback`
 
-
 ### with\_tmpdir
 
 `with_tmpdir ([parent_dir,] templ, callback)`
@@ -239,6 +238,28 @@ Returns:
 
 -   The result of the call to `callback`.
 
+### with\_wd
+
+`with_wd (directory, callback)`
+
+Run an action within a different directory. This function will
+change the working directory to `directory`, execute `callback`,
+then switch back to the original working directory, even if an
+error occurs while running the callback action.
+
+Parameters:
+
+`directory`
+:   Directory in which the given `callback` should be executed
+    (string)
+
+`callback`
+:   Action to execute in the given directory (function)
+
+Returns:
+
+-   The result(s) of the call to `callback`
+
 
 License
 -------

src/Foreign/Lua/Module/System.hs

@@ -32,6 +32,7 @@ module Foreign.Lua.Module.System (
   , tmpdirname
   , with_env
   , with_tmpdir
+  , with_wd
   )
 where
 
@@ -73,6 +74,7 @@ pushModule = do
   addFunction "tmpdirname" tmpdirname
   addFunction "with_env" with_env
   addFunction "with_tmpdir" with_tmpdir
+  addFunction "with_wd" with_wd
   return 1
 
 -- | Add the @system@ module under the given name to the table of
@@ -162,6 +164,17 @@ setenv name value = ioToLua (Env.setEnv name value)
 tmpdirname :: Lua FilePath
 tmpdirname = ioToLua Directory.getTemporaryDirectory
 
+-- | Run an action in a different directory, then restore the old
+-- working directory.
+with_wd :: FilePath -> Callback -> Lua NumResults
+with_wd fp callback =
+  bracket (Lua.liftIO Directory.getCurrentDirectory)
+          (Lua.liftIO . Directory.setCurrentDirectory)
+          $ \_ -> do
+              Lua.liftIO (Directory.setCurrentDirectory fp)
+              callback `invokeWithFilePath` fp
+
+
 -- | Run an action, then restore the old environment variable values.
 with_env :: Map.Map String String -> Callback -> Lua NumResults
 with_env environment callback =

test/system-module-tests.lua

@@ -110,3 +110,15 @@ assert(in_tmpdir(create_then_count_files) == 1, 'Number of files should be 1')
 system.setenv('TESTING', token)
 assert(system.getenv 'TESTING' == token,
        'setting and getting env var is inconsistent')
+
+-- with_wd
+local cwd = system.getwd()
+function check_wd (path)
+  assert(path == system.getwd(), "current path is given as arg")
+  assert(path ~= cwd, "current path has changed from original")
+end
+
+system.with_tmpdir(
+  'wd-test',
+  function (path) return system.with_wd(path, check_wd) end
+)