From 831620c6ae0461228e0801de92dfc6671333a079 Mon Sep 17 00:00:00 2001
From: Ben Sima <ben@bsima.me>
Date: Fri, 27 Mar 2020 12:11:31 -0700
Subject: Refactor and remove custom operators

As much as I like these operators, I have to remove them because they
don't work as expected. Haskell doesn't allow you to have unary prefix
operators. I can't find a way around this, and it's not that important
anyway.
---
 Com/Simatime/Go.hs | 125 ++++++++++++++++++++---------------------------------
 1 file changed, 48 insertions(+), 77 deletions(-)

(limited to 'Com/Simatime')

diff --git a/Com/Simatime/Go.hs b/Com/Simatime/Go.hs
index 1b32230..0eef38d 100644
--- a/Com/Simatime/Go.hs
+++ b/Com/Simatime/Go.hs
@@ -1,100 +1,71 @@
--- based on
--- https://stackoverflow.com/questions/4522387/how-can-i-emulate-gos-channels-with-haskell
--- but this version encodes end-of-stream on the communication channel, as a Nothing
+{- | A Go-like EDSL to make working with concurrent in-process code a bit
+   easier to read.
 
+This module is expected to be imported qualified as `Go`.
+
+$example
+-}
+{-# LANGUAGE NoImplicitPrelude #-}
 module Com.Simatime.Go
-  ( chan
-  , readCh
-  , (-<-)
-  , writeCh
-  , (->-)
-  , go
+  (
+  -- * Running and forking
+    Go
+  , run
+  , fork
+  -- * Channels
+  , Channel
+  , chan
+  , read
+  , write
   )
 where
 
 import           Control.Concurrent             ( forkIO
                                                 , ThreadId
-                                                , threadDelay
                                                 )
 import           Control.Concurrent.STM.TChan   ( newTChan
                                                 , readTChan
                                                 , writeTChan
-                                                , isEmptyTChan
                                                 , TChan
                                                 )
-import           Control.Monad                  ( forM_ )
-import           GHC.Conc                       ( atomically )
-
--- | Make a new channel.
-chan :: _
-chan = atomically . newTChan
-
--- | Take from a channel.
-readCh :: TChan a -> IO a
-readCh = atomically . readTChan
-
--- | Alias for 'readCh'.
---
--- >>> c <- chan
--- >>> writeCh c "val"
--- >>> -<- c
--- "val"
---
--- I don't think this looks terrible with do-notation:
---
--- >>> c <- chan
--- >>> writeCh c "val"
--- >>> result <- -<- c
--- >>> print result
--- "val"
-(-<-) :: TChan a -> IO a
-(-<-) = readCh
-
--- | Write to a channel.
-writeCh :: TChan a -> a -> IO ()
-writeCh ch v = atomically $ writeTChan ch v
+import           GHC.Conc                       ( STM
+                                                , atomically
+                                                )
+import           Protolude                      ( IO()
+                                                , MonadIO(liftIO)
+                                                , flip
+                                                , (.)
+                                                )
+type Go = STM
+type Channel = TChan
 
--- | Alias for 'writeCh', but flipped to make it read better.
---
--- >>> c <- chan
--- >>> "val" ->- c
--- >>> readCh c
--- "val"
-(->-) :: TChan a -> a -> IO ()
-(->-) = flip writeCh
+-- | Runs a Go command in IO.
+run :: Go a -> IO a
+run = atomically
 
 -- | Starts a background process.
-go :: IO () -> IO ThreadId
-go = forkIO
+fork :: IO () -> IO ThreadId
+fork = forkIO
 
+-- | Make a new channel.
+chan :: Go (Channel a)
+chan = newTChan
 
-{- Example: (TODO: move to module-level docs)
+-- | Take from a channel. Blocks until a value is received.
+read :: Channel a -> Go a
+read = readTChan
 
--- can I just implement forM/Traversable over the channel?
-forRange :: TChan (Maybe a) -> (a -> IO b) -> IO [b]
-forRange ch fn = helper fn [] where
-  -- helper :: (a -> IO b) -> [b] -> IO [b]
-  helper fn acc = do
-    jv <- readCh ch
-    case jv of
-      Nothing -> return $ reverse acc
-      Just v  -> do
-        b <- fn v
-        helper fn (b : acc)
+-- | Write to a channel.
+write :: Channel a -> a -> Go ()
+write = writeTChan
 
-feedData :: (Num a, Enum a) => TChan (Maybe a) -> IO ()
-feedData ch = do
-  forM_ [1 .. 9999] (\x -> writeCh ch (Just x))
-  writeQ ch Nothing -- EOF value
+{- $example
 
-printData :: TChan (Maybe Int) -> IO ()
-printData c = do
-  forRange c (print :: Int -> IO ())
-  return ()
+A simple example from ghci:
 
-main :: IO ()
-main = do
-  ch <- chan
-  go $ feedData ch
-  printData ch
+>>> import qualified Com.Simatime.Go as Go
+>>> c <- Go.run Go.chan :: IO (Go.Channel Text)
+>>> Go.run $ Go.write c "test"
+>>> Go.run $ Go.read c
+"test"
 -}
-- 
cgit v1.2.3