A Haskell client for kRPC
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KRPC Hors-Service

KRPC Hors-Service is a client for kRPC -- a mod for Kerbal Space Program -- written in Haskell. Please refer to the kRPC documentation for a detailed list of available RPC calls.

How to use

  • The simplest way to use this library is with Stack by adding the dependence to your project's stack.yaml file (replace vX.Y.Z by the release tag you want to use or a commit hash):

    # Local packages, usually specified by relative directory name
    - '.'
    - extra-dep: true
        git: git@github.com:cahu/krpc-hs
        commit: vX.Y.Z
  • Alternatively, you can clone the project in a directory of your choice and run these commands:

    ~/krpc-hs$ stack build

    You can use haddock to generate basic documentation, for instance:

    ~/krpc-hs$ stack haddock

    Tell stack where to find krpc-hs in your project's stack.yaml file:

    # Local packages, usually specified by relative directory name
    - '.'
    - '/home/user/krpc-hs'
  • If you don't want to use stack, then the usual cabal build should work with maybe some small tweaking of the .cabal file.


Complete working examples can be found in the examples folder.

Simple RPC

import KRPCHS
import KRPCHS.UI
import KRPCHS.SpaceCenter

main :: IO ()
main =
    -- Let's start by creating an RPCClient
    withRPCClient "Demo" "" "50000" $ \client -> do
        -- From here, you can run programs that live in an RPCContext
        runRPCProg client liftOffProgram
        runRPCProg client munTransferProgram
        runRPCProg client munLandingProgram

liftOffProgram :: RPCContext ()
liftOffProgram = do
	countDown 10          -- call another program
    ut <- getUT           -- get the date
    v  <- getActiveVessel -- get our current vessel
    ... do some other things

munTransferProgram :: RPCContext ()
munTransferProgram = do

munLandingProgram :: RPCContext ()
munLandingProgram = do

countDown :: Int -> RPCContext ()
countDown n = forM_ (reverse [ 1 .. n ]) $ \sec -> do
    void   $ message (T.pack $ show sec) 1 MessagePosition'TopCenter
    liftIO $ threadDelay 1000000

Using streams

import KRPCHS
import KRPCHS.SpaceCenter

main :: IO ()
main =
    withRPCClient    "Demo" "" "50000" $ \client ->
    withStreamClient client "" "50001" $ \streamClient ->
        runRPCProg client (exampleProg streamClient)

exampleProg :: StreamClient -> RPCContext ()
exampleProg streamClient = do
    utStream <- getUTStream
    forever $ do
        msg <- getStreamMessage streamClient
        when (messageHasResultFor utStream msg) $ do
            ut <- getStreamResult utStream msg
            liftIO $ putStrLn (show ut)


  • RPCContext is a ReaderT on top of IO and it derives MonadThrow, MonadCatch, MonadMask (from the exception module).
  • You should always check that a stream message has a result for the stream you are going to use with messageHasResultFor because there will be some delay between the moment you ask for a new stream and the moment you start receiving results. In the event you use getStreamResult on a message with no result for the specified stream, an exception will be thrown.