Using Haskell to put timestamp in filenames-CodePudding

Long story short: I am using XMonad and trying to put dynamic timestamps on screen-recordings.

I could have cheated and solved this by making it a bash script that easily lets you use changing timestamps, but I figured it was a good opportunity to dig into meat of Haskell.

The code I have tried to use:

import Data.Time
timeStamp = formatTime defaultTimeLocale "%Y-%m-%d—%H:%M:%S" <$> getCurrentTime

then in keybindings I have put

        , ("M-<Print>", spawn $ "giph -f 60 -y -s  ~/recordings/"    timeStamp    ".mp4")

which give me the error of

 • Couldn't match expected type ‘[Char]’ with actual type ‘IO String’

I figured this is related to Haskell not letting its variables change value, but I have no idea how to work around this or how to rewrite it so that I wouldn't need to work around it.

CodePudding user response：

With = you have just defined another function. Use <- to bind the result of a monadic action to a variable:

timeStamp <- formatTime defaultTimeLocale "%Y-%m-%d—%H:%M:%S" <$> getCurrentTime

-- ...

"~/recordings/"    timeStamp    ".mp4"

CodePudding user response：

In Haskell, you cannot "mix" IO with generic types. There are ways to get around this, though. For example, you could use the following to utilize an IO String as a generic String

myIOThing >>= \regular -> <do_something>

You can find more about it here https://wiki.haskell.org/How_to_get_rid_of_IO#Using_I.2FO_actions_more_directly