src/Elm/Utils.hs · elk

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elk/src/Elm/Utils.hs

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1{-# OPTIONS_GHC -Wall #-}

2{-# LANGUAGE FlexibleContexts #-}

3module Elm.Utils ((|>), (<|), getAsset, run, unwrappedRun, CommandError(..)) where

5import Control.Monad.Error (MonadError, MonadIO, liftIO, throwError)

6import System.Directory (doesFileExist)

7import System.Environment (getEnv)

8import System.Exit (ExitCode(ExitSuccess, ExitFailure))

9import System.FilePath ((</>))

10import System.IO.Error (tryIOError)

11import System.Process (readProcessWithExitCode)

14{-| Forward function application `x |> f == f x`. This function is useful

15for avoiding parenthesis and writing code in a more natural way.

16-}

17(|>) :: a -> (a -> b) -> b

18x |> f = f x

21{-| Backward function application `f <| x == f x`. This function is useful for

22avoiding parenthesis.

23-}

24(<|) :: (a -> b) -> a -> b

25f <| x = f x

28infixr 0 <|

29infixl 0 |>

32-- RUN EXECUTABLES

34data CommandError

35 = MissingExe String

36 | CommandFailed String String

39{-| Run a command, throw an error if the command is not found or if something

40goes wrong.

41-}

42run :: (MonadError String m, MonadIO m) => String -> [String] -> m String

43run command args =

44 do result <- liftIO (unwrappedRun command args)

45 case result of

46 Right out -> return out

47 Left err ->

48 throwError (context (message err))

49 where

50 context msg =

51 "failure when running:" ++ concatMap (' ':) (command:args) ++ "\n" ++ msg

53 message err =

54 case err of

55 CommandFailed stderr stdout ->

56 stdout ++ stderr

57 MissingExe msg ->

58 msg

61unwrappedRun :: String -> [String] -> IO (Either CommandError String)

62unwrappedRun command args =

63 do (exitCode, stdout, stderr) <- readProcessWithExitCode command args ""

64 return $

65 case exitCode of

66 ExitSuccess -> Right stdout

67 ExitFailure code

68 | code == 127 -> Left (missingExe command) -- UNIX

69 | code == 9009 -> Left (missingExe command) -- Windows

70 | otherwise -> Left (CommandFailed stdout stderr)

73missingExe :: String -> CommandError

74missingExe command =

75 MissingExe $

76 "Could not find command '" ++ command ++ "'. Do you have it installed?\n\

77 \ Can it be run from anywhere? Is it on your PATH?"

81-- GET STATIC ASSETS

83{-| Get the absolute path to a data file. If you install with cabal it will look

84-}

85getAsset :: String -> (FilePath -> IO FilePath) -> FilePath -> IO FilePath

86getAsset project getDataFileName name =

87 do path <- getDataFileName name

88 exists <- doesFileExist path

89 if exists

90 then return path

91 else do

92 environment <- tryIOError (getEnv "ELM_HOME")

93 case environment of

94 Right env ->

95 return (env </> project </> name)

97 Left _ ->

98 fail (errorNotFound name)

100

101errorNotFound :: FilePath -> String

102errorNotFound name =

103 unlines

104 [ "Unable to find the ELM_HOME environment variable when searching"

105 , "for the " ++ name ++ " file."

106 , ""

107 , "If you installed Elm Platform with the Mac or Windows installer, it looks like"

108 , "ELM_HOME was not set automatically. Look up how to set environment variables"

109 , "on your platform and set ELM_HOME to the directory that contains Elm's static"