From 80913aeed46fc607f057a77ffdd884b5db77a0bc Mon Sep 17 00:00:00 2001
From: Pavan Rikhi <pavan.rikhi@gmail.com>
Date: Thu, 9 Apr 2020 13:51:37 -0400
Subject: Add a HandleReader Plugin
This adds a new `HandleReader` plugin, which displays data from a
Haskell `Handle`. This is really only useful if you are running xmobar
from within another Haskell program, but lets you avoid the mechanics of
creating a named pipe with the proper file permissions.
Instead, you can use `System.Process.createPipe` to make a pair of read
& write Handles. If you pass the read handle to HandleReader, you can
use hPutStr on the write Handle to send data to xmobar from your
application code.
---
src/Xmobar/Plugins/HandleReader.hs | 70 ++++++++++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)
create mode 100644 src/Xmobar/Plugins/HandleReader.hs
(limited to 'src/Xmobar/Plugins')
diff --git a/src/Xmobar/Plugins/HandleReader.hs b/src/Xmobar/Plugins/HandleReader.hs
new file mode 100644
index 0000000..e1ee6a5
--- /dev/null
+++ b/src/Xmobar/Plugins/HandleReader.hs
@@ -0,0 +1,70 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module : Plugins.HandleReader
+-- Copyright : (c) Pavan Rikhi
+-- License : BSD-style (see LICENSE)
+--
+-- Maintainer : Pavan Rikhi <pavan.rikhi@gmail.com>
+-- Stability : unstable
+-- Portability : portable
+--
+-- A plugin for reading from 'Handle's
+--
+-----------------------------------------------------------------------------
+
+module Xmobar.Plugins.HandleReader
+ ( HandleReader(..)
+ )
+where
+
+import System.IO ( Handle
+ , hIsEOF
+ )
+
+import Xmobar.Run.Exec ( Exec(..) )
+import Xmobar.System.Utils ( hGetLineSafe )
+
+
+-- | A HandleReader displays any text received from a Handle.
+--
+-- This is only useful if you are running @xmobar@ from other Haskell code.
+-- You can create a pair of @(read, write)@ 'Handle's using
+-- 'System.Process.createPipe'. Pass the @read@ 'Handle' to HandleReader
+-- and write your desired output to the @write@ 'Handle'.
+--
+-- @
+-- (readHandle, writeHandle) <- 'System.Process.createPipe'
+-- xmobarProcess <- 'System.Posix.Process.forkProcess' $ 'Xmobar.xmobar' myConfig
+-- { commands =
+-- 'Xmobar.Run' ('HandleReader' readHandle "handle") : 'Xmobar.commands' myConfig
+-- }
+-- 'System.IO.hPutStr' writeHandle "Hello World"
+-- @
+data HandleReader
+ = HandleReader
+ Handle
+ -- ^ The Handle to read from.
+ String
+ -- ^ Alias for the HandleReader
+ deriving (Show)
+
+-- | WARNING: This Read instance will throw an exception if used! It is
+-- only implemented because it is required to use HandleReader with
+-- 'Xmobar.Run' in 'Xmobar.commands'.
+instance Read HandleReader where
+ -- | Throws an 'error'!
+ readsPrec = error "HandleReader: Read instance is stub"
+
+-- | Asynchronously read from the 'Handle'.
+instance Exec HandleReader where
+ -- | Read from the 'Handle' until it is closed.
+ start (HandleReader handle _) cb =
+ untilM (hIsEOF handle) $ hGetLineSafe handle >>= cb
+ -- | Use the 2nd argument to HandleReader as its alias.
+ alias (HandleReader _ a) = a
+
+-- Loop the action until predicateM returns True.
+untilM :: Monad m => m Bool -> m () -> m ()
+untilM predicateM action = do
+ predicate <- predicateM
+ if predicate then return () else action >> untilM predicateM action
--
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