How to convert list to JSVal?

Question

I'm trying to build JS FFI for some JS library to get it work with GHCJS and I need to convert list to single JSVal

listToJSVal :: PToJSVal a => [a] -> JSVal
listToJSVal = map pToJSVal

but get error

 Couldn't match type ‘[JSVal]’ with ‘JSVal’
    Expected type: [a] -> JSVal
      Actual type: [a] -> [JSVal]

obviously, I need concat function, but using mconcat gives

Could not deduce (Monoid JSVal) arising from a use of ‘mconcat’
    from the context (PToJSVal a)
      bound by the type signature for

Maybe, there is easier way how to do this conversion properly?

score 2 · Answer 1 · answered Aug 10 '16 at 20:05

Also you could convert it at hand:

{-# LANGUAGE QuasiQuotes #-}

import GHCJS.Marshal.Pure
import GHCJS.Types
import GHCJS.Foreign.QQ 
import GHCJS.Prim

listToJSVal :: PToJSVal a => [a] -> JSVal
listToJSVal xs = foldl push ar xs 
    where ar = [js'| [] |]
          push as x = [js'| { `as.push(`x); $r = `as } |]

printArray :: JSVal -> IO ()
printArray as = [js_| for(i = 0;i < `as.length;i++) { console.log(`as[i]) } |]

main = do 
     printArray $ listToJSVal ([1,2,3,4,5]::[Int])

score 1 · Answer 2 · answered Jun 16 '16 at 15:17

1

It appears that pToJSVal is only defined for base types.

For conversion of arbitrary values to JS, I would try the toJSVal and toJSValListOf functions defined in GHCJS/Marshal/Internal.hs (link)

answered Jun 16 '16 at 15:17

ErikR

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I tried those, but it use `IO`, but I have pure code and bringing IO will break all my pipeline – sigrlami Jun 16 '16 at 15:27
@Sigrlami this looks like an ok situation for unsafePerformIO ? – sclv Jul 11 '16 at 06:41

How to convert list to JSVal?

2 Answers2