Add environment variable functions

Add functions `getenv`, `setenv`, and `env`.

Author: tarleb

README.md

@@ -48,6 +48,34 @@ Returns:
 
 - The current working directory (string).
 
+### env {#system-env}
+
+`env ()`
+
+Retrieve the entire environment.
+
+Returns:
+
+- A table mapping environment variables names to their string value
+  (table).
+
+### getenv {#system-getenv}
+
+`getenv (var)`
+
+Return the value of the environment variable `var`, or `nil` if there
+is no such value.
+
+Parameters:
+
+`var`:
+:   name of the environment variable (string)
+
+Returns:
+
+- value of the variable, or nil if the variable is not defined (string
+  or nil).
+
 ### ls {#system-ls}
 
 `ls ([directory])`
@@ -59,7 +87,7 @@ Parameters:
 `directory`:
 :   Path of the directory whose contents should be listed (string).
     Defaults to `.`.
-    
+
 Returns:
 
 - A table of all entries in `directory` without the special entries (`.`
@@ -71,6 +99,20 @@ Returns:
 
 An alias for [`currentdir`](#system-currentdir)
 
+### setenv {#system-setenv}
+
+`setenv (var, value)`
+
+Set the specified environment variable to a new value.
+
+Parameters:
+
+`var`:
+:   name of the environment variable (string).
+
+`value`:
+:   new value (string).
+
 ### tmpdirname {#system-tmpdirname}
 
 `tmpdirname ()`
@@ -91,7 +133,7 @@ The operation may fail if the operating system has no notion of
 temporary directory.
 
 The function doesn't verify whether the path exists.
-    
+
 Returns:
 
 - The current directory for temporary files (string).
@@ -116,7 +158,7 @@ Parameters:
 `callback`:
 :   Function which takes the name of the temporary directory as its
     first argument (function).
-    
+
 Returns:
 
 -   The result of the call to `callback`.

src/Foreign/Lua/Module/System.hs

@@ -25,6 +25,7 @@ import System.IO.Error (IOError, isDoesNotExistError)
 
 import qualified Foreign.Lua as Lua
 import qualified System.Directory as Directory
+import qualified System.Environment as Env
 import qualified System.IO.Temp as Temp
 
 -- | Pushes the @text@ module to the lua stack.
@@ -33,8 +34,11 @@ pushModule = do
   Lua.newtable
   addFunction "chdir" chdir
   addFunction "currentdir" currentdir
+  addFunction "env" env
+  addFunction "getenv" getenv
   addFunction "ls" ls
   addFunction "pwd" currentdir
+  addFunction "setenv" setenv
   addFunction "tmpdirname" tmpdirname
   addFunction "with_tmpdir" with_tmpdir
   return 1
@@ -135,6 +139,23 @@ chdir fp = ioToLua $ Directory.setCurrentDirectory fp
 currentdir :: Lua FilePath
 currentdir = ioToLua Directory.getCurrentDirectory
 
+-- | Retrieve the entire environment
+env :: Lua NumResults
+env = do
+  kvs <- ioToLua Env.getEnvironment
+  let addValue (k, v) = Lua.push k *> Lua.push v *> Lua.rawset (-3)
+  Lua.newtable
+  mapM_ addValue kvs
+  return (NumResults 1)
+
+-- | Returns the value of an environment variable
+getenv :: String -> Lua (Optional String)
+getenv name = ioToLua (Optional <$> Env.lookupEnv name)
+
+-- | Set the specified environment variable to a new value.
+setenv :: String -> String -> Lua ()
+setenv name value = ioToLua (Env.setEnv name value)
+
 -- | Convert a System IO operation to a Lua operation.
 ioToLua :: IO a -> Lua a
 ioToLua action = do

test/system-module-tests.lua

@@ -19,6 +19,9 @@ assert(system.with_tmpdir('foo', write_read_token) == token)
 -- tmpdirname
 assert(type(system.tmpdirname()) == 'string', "tmpdirname should return a string")
 
+-- env
+assert(type(system.env()) == 'table')
+
 -- ls
 assert(type(system.ls('.')) == 'table')
 assert(#system.ls('.') == #system.ls())
@@ -52,3 +55,7 @@ function create_then_count_files ()
 end
 
 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')