Slightly higher level wrapper for creating GHCi-like REPL monads that are composable with normal MTL transformers. Mostly exists because I got tired of implementing the same interface for simple shells over and over and decided to canonize the giant pile of hacks that I use to make Haskeline work.
See Documentation for more detailed usage.
This release adds two parameters to the ReplOpts constructor and evalRepl function.
finalisermultilineCommand
The finaliser function is a function run when the Repl monad is is exited.
-- | Decide whether to exit the REPL or not
data ExitDecision
= Continue -- | Keep the REPL open
| Exit -- | Close the REPL and exitFor example:
final :: Repl ExitDecision
final = do
liftIO $ putStrLn "Goodbye!"
return ExitThe multilineCommand argument takes a command which invokes a multiline edit
mode in which the user can paste/enter text across multiple lines terminating
with a Ctrl-D / EOF. This can be used in conjunction with a customBanner
function to indicate the entry mode.
customBanner :: MultiLine -> Repl String
customBanner SingleLine = pure ">>> "
customBanner MultiLine = pure "| "See Multiline for a complete example.
The underlying haskeline library that provides readline support had a breaking
API change in 0.8.0.0 which removed the bespoke
System.Console.Haskeline.MonadException module in favour of using the
exceptions package. This is a much better design and I strongly encourage
upgrading. To migrate simply add the following bounds to your Cabal file.
build-depends:
repline >= 0.3.0.0
haskeline >= 0.8.0.0You may also need to add the following to your stack.yaml file if using Stack.
resolver: lts-15.0
packages:
- .
extra-deps:
- haskeline-0.8.0.0
- repline-0.3.0.0type Repl a = HaskelineT IO a
-- Evaluation : handle each line user inputs
cmd :: String -> Repl ()
cmd input = liftIO $ print input
-- Tab Completion: return a completion for partial words entered
completer :: Monad m => WordCompleter m
completer n = do
let names = ["kirk", "spock", "mccoy"]
return $ filter (isPrefixOf n) names
-- Commands
help :: [String] -> Repl ()
help args = liftIO $ print $ "Help: " ++ show args
say :: [String] -> Repl ()
say args = do
_ <- liftIO $ system $ "cowsay" ++ " " ++ (unwords args)
return ()
options :: [(String, [String] -> Repl ())]
options = [
("help", help) -- :help
, ("say", say) -- :say
]
ini :: Repl ()
ini = liftIO $ putStrLn "Welcome!"
repl :: IO ()
repl = evalRepl (pure ">>> ") cmd options Nothing (Word completer) iniTrying it out:
$ stack repl Simple.hs
Prelude> main
Welcome!
>>> <TAB>
kirk spock mccoy
>>> k<TAB>
kirk
>>> spam
"spam"
>>> :say Hello Haskell
_______________
< Hello Haskell >
---------------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||Quite often tab completion is dependent on the internal state of the Repl so we'd like to query state of the
interpreter for tab completions based on actions performed themselves within the Repl, this is modeleted
naturally as a monad transformer stack with StateT on top of HaskelineT.
type IState = Set.Set String
type Repl a = HaskelineT (StateT IState IO) a
-- Evaluation
cmd :: String -> Repl ()
cmd input = modify $ \s -> Set.insert input s
-- Completion
comp :: (Monad m, MonadState IState m) => WordCompleter m
comp n = do
ns <- get
return $ filter (isPrefixOf n) (Set.toList ns)
-- Commands
help :: [String] -> Repl ()
help args = liftIO $ print $ "Help!" ++ show args
puts :: [String] -> Repl ()
puts args = modify $ \s -> Set.union s (Set.fromList args)
opts :: [(String, [String] -> Repl ())]
opts = [
("help", help) -- :help
, ("puts", puts) -- :puts
]
ini :: Repl ()
ini = return ()
-- Tab completion inside of StateT
repl :: IO ()
repl = flip evalStateT Set.empty
$ evalRepl (pure ">>> ") cmd opts Nothing (Word comp) iniJust as GHCi will provide different tab completion for kind-level vs type-level symbols based on which prefix
the user has entered, we can also set up a provide this as a first-level construct using a Prefix tab
completer which takes care of the string matching behind the API.
type Repl a = HaskelineT IO a
-- Evaluation
cmd :: String -> Repl ()
cmd input = liftIO $ print input
-- Prefix tab completeter
defaultMatcher :: MonadIO m => [(String, CompletionFunc m)]
defaultMatcher = [
(":file" , fileCompleter)
, (":holiday" , listCompleter ["christmas", "thanksgiving", "festivus"])
]
-- Default tab completer
byWord :: Monad m => WordCompleter m
byWord n = do
let names = ["picard", "riker", "data", ":file", ":holiday"]
return $ filter (isPrefixOf n) names
files :: [String] -> Repl ()
files args = liftIO $ do
contents <- readFile (unwords args)
putStrLn contents
holidays :: [String] -> Repl ()
holidays [] = liftIO $ putStrLn "Enter a holiday."
holidays xs = liftIO $ do
putStrLn $ "Happy " ++ unwords xs ++ "!"
opts :: [(String, [String] -> Repl ())]
opts = [
("file", files)
, ("holiday", holidays)
]
init :: Repl ()
init = return ()
repl :: IO ()
repl = evalRepl (pure ">>> ") cmd opts Nothing (Prefix (wordCompleter byWord) defaultMatcher) initTrying it out:
$ stack repl examples/Prefix.hs
Prelude> main
>>> :file <TAB>
sample1.txt sample2.txt
>>> :file sample1.txt
>>> :holiday <TAB>
christmas thanksgiving festivusCopyright (c) 2014-2020, Stephen Diehl Released under the MIT License
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