haste-compiler- Haskell To ECMAScript compiler

Safe HaskellNone



Wraps Haste.Concurrent to work with Haste.App. Task switching happens whenever a thread is blocked in an MVar, so things like polling an IORef in a loop will starve all other threads.

This will likely be the state of Haste concurrency until Javascript gains decent native concurrency support.



data MVar a

data MBox t a

An MBox is a read/write-only MVar, depending on its first type parameter. Used to communicate with server processes.

data Send

data Recv

type Inbox = MBox Recv

class Monad m => MonadConc m where

Any monad which supports concurrency.


liftConc :: CIO a -> m a

fork :: m () -> m ()


forkMany :: [Client ()] -> Client ()

Spawn several concurrent computations.

newMVar :: a -> Client (MVar a)

Create a new MVar with the specified contents.

newEmptyMVar :: Client (MVar a)

Create a new empty MVar.

takeMVar :: MVar a -> Client a

Read the value of an MVar. If the MVar is empty, takeMVar blocks until a value arrives. takeMVar empties the MVar.

putMVar :: MVar a -> a -> Client ()

Put a value into an MVar. If the MVar is full, putMVar will block until the MVar is empty.

peekMVar :: MVar a -> Client (Maybe a)

Read an MVar without affecting its contents. If the MVar is empty, peekMVar immediately returns Nothing.

readMVar :: MVar a -> Client a

Read an MVar then put it back. As Javascript is single threaded, this function is atomic. If this ever changes, this function will only be atomic as long as no other thread attempts to write to the MVar.

spawn :: MonadConc m => (Inbox a -> m ()) -> m (Outbox a)

Creates a generic process and returns a MBox which may be used to pass messages to it. While it is possible for a process created using spawn to transmit its inbox to someone else, this is a very bad idea; don't do it.

receive :: MonadConc m => Inbox a -> m a

Block until a message arrives in a mailbox, then return it.

statefully :: MonadConc m => st -> (st -> evt -> m (Maybe st)) -> m (Outbox evt)

Creates a generic stateful process. This process is a function taking a state and an event argument, returning an updated state or Nothing. statefully creates a MBox that is used to pass events to the process. Whenever a value is written to this MBox, that value is passed to the process function together with the function's current state. If the process function returns Nothing, the process terminates. If it returns a new state, the process again blocks on the event MBox, and will use the new state to any future calls to the server function.

(!) :: MonadConc m => Outbox a -> a -> m ()

Write a value to a MBox. Named after the Erlang message sending operator, as both are intended for passing messages to processes. This operation does not block until the message is delivered, but returns immediately.

(<!) :: MonadConc m => Outbox a -> m a -> m ()

Perform a Client computation, then write its return value to the given pipe. Mnemonic: the operator is a combination of <- and !. Just like (!), this operation is non-blocking.

forever :: Monad m => m a -> m b

forever act repeats the action infinitely.