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https://github.com/sdiehl/repline

Haskeline wrapper for GHCi-like REPL interfaces
https://github.com/sdiehl/repline

command-line haskell haskell-library readline repl

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Haskeline wrapper for GHCi-like REPL interfaces

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Repline

-------



[![Build Status](https://travis-ci.org/sdiehl/repline.svg?branch=master)](https://travis-ci.org/sdiehl/repline)

[![Hackage](https://img.shields.io/hackage/v/repline.svg)](https://hackage.haskell.org/package/repline)



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](https://hackage.haskell.org/package/repline-0.4.0.0/docs/System-Console-Repline.html)

for more detailed usage.



Examples

--------



* [Simple](examples/Simple.hs)

* [Prefix](examples/Prefix.hs)

* [Stateful](examples/Stateful.hs)

* [Multiline](examples/Multiline.hs)



Migration from 0.3.x

--------------------



This release adds two parameters to the `ReplOpts` constructor and `evalRepl` function.



* `finaliser`

* `multilineCommand`



The `finaliser` function is a function run when the Repl monad is is exited.



```haskell

-- | Decide whether to exit the REPL or not

data ExitDecision

  = Continue -- | Keep the REPL open

  | Exit     -- | Close the REPL and exit

```



For example:



```haskell

final :: Repl ExitDecision

final = do

  liftIO $ putStrLn "Goodbye!"

  return Exit

```



The `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.



```haskell

customBanner :: MultiLine -> Repl String

customBanner SingleLine = pure ">>> "

customBanner MultiLine = pure "| "

```



See [Multiline](examples/Multiline.hs) for a complete example.



Migration from 0.2.x

--------------------



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.



```yaml

build-depends:

  repline   >= 0.3.0.0

  haskeline >= 0.8.0.0

```



You may also need to add the following to your `stack.yaml` file if using Stack.



```yaml

resolver: lts-15.0

packages:

  - .

extra-deps:

  - haskeline-0.8.0.0

  - repline-0.3.0.0

```



Usage

-----



```haskell

type 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) ini

```



Trying it out:



```haskell

$ stack repl Simple.hs

Prelude> main



Welcome!

>>> 

kirk spock mccoy



>>> k

kirk



>>> spam

"spam"



>>> :say Hello Haskell

 _______________

< Hello Haskell >

 ---------------

        \   ^__^

         \  (oo)\_______

            (__)\       )\/\

                ||----w |

                ||     ||

```



Stateful Tab Completion

-----------------------



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``.



```haskell

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) ini

```



Prefix Completion

-----------------



Just 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.



```haskell

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) init

```



Trying it out:



```haskell

$ stack repl examples/Prefix.hs

Prelude> main



>>> :file 

sample1.txt sample2.txt



>>> :file sample1.txt



>>> :holiday 

christmas thanksgiving festivus

```



License

-------



Copyright (c) 2014-2020, Stephen Diehl

Released under the MIT License