How to get the current time with GHCJS?

Question

How to get the current time with GHCJS? Should i try to access Date or use Haskell base libraries? Is there an utility function somewhere in the GHCJS base libraries?

The haskell libraries seem to work - any reason not to use them? — ondra, Dec 02 '15 at 21:32
I think that i did not find a way to use them. Would you write an answer here about your idea? I will try it and mark it as the correct answer if it will work — danza, Dec 04 '15 at 10:29

score 4 · Accepted Answer · answered Dec 04 '15 at 11:55

4

The Data.Time.Clock module seems to work well:

import Data.Time.Clock (getCurrentTime)
import Data.Time.Format -- Show instance
main = do
  now <- getCurrentTime
  print now

answered Dec 04 '15 at 11:55

ondra

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Yes, this works, and it is way cleaner, thanks! This introduces a dependency on `time` – danza Dec 07 '15 at 18:08

score 0 · Answer 2 · answered Nov 09 '15 at 17:09

The solution i found currently is quite ugly, but it works for me, so maybe it can save some time to somebody:

{-# LANGUAGE JavaScriptFFI #-}

import GHCJS.Types( JSVal )
import GHCJS.Prim( fromJSString )

foreign import javascript unsafe "Date.now()+''" dateNow :: IO (JSVal)

asInteger = read (fromJSString dateNow) :: Integer -- this happens in IO

The ugliness comes from not finding a JSInteger type in GHCJS, which would be needed in order to get the result of Date.now() which is a long integer. So i need to produce a string concatenating a string to the result of Date.now() in Javascript. At this point i could get a JSString as result, but that would not be an instance of Read so using read would not work. So i get a JSValue and convert it to String using fromJSString.

Eventually there might be a JSInteger in GHCJS, or JSString might become an instance of Read, so if you are reading this from the future try out something more elegant!

How to get the current time with GHCJS?

2 Answers2