create file if does not exist

src/App/Gui.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TemplateHaskell   #-}
 
 module Gui (runEditor) where
@@ -17,6 +18,10 @@ import qualified Graphics.Vty           as Vty
 import           Data.Text              (pack, singleton)
 import           Data.Text.Markup       (Markup, (@@))
 
+---- Files ----
+import           System.IO              (IOMode (..), hClose, hGetContents,
+                                         openFile)
+
 ---- Various ----
 import           Control.Monad.IO.Class (liftIO)
 import           Data.List
@@ -45,8 +50,19 @@ makeLenses ''HeditState
 
 runEditor :: FilePath -> IO ()
 runEditor f = do
-  content <- readFile f
+  handle  <- openFile f ReadWriteMode -- creates file if it does not exist
-  _       <- BrickMain.defaultMain theApp (initialState f content)
+  content <- hGetContents handle
+  {-
+     reads the content before closing the handle (non-lazy)
+     this is the version with the fewest "dependecies"
+     other options:
+     - ByteString.hGetContents: strict, fast
+         -> ByteString.Lazy for lazy, fast
+     - Text.IO.hGetContents: strict, needs 2x file size while reading in
+         -> filesize == 2xRAM = bad
+  -}
+  content `seq` hClose handle
+  BrickMain.defaultMain theApp (initialState f content)
   return ()
 
 theApp :: App HeditState Vty.Event Names