Halogen: TypeError: eff is not a function

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#1

I’m building a small web app in Halogen and I just wrapped a little bit of Javascript to close a Bootstrap modal. Javascript:

exports.hide = modalId => {
    $('#'+modalId).modal("hide");
}

Purescript:

module App.Modal where

import Data.Unit (Unit)
import Effect (Effect)

foreign import hide :: String -> Effect Unit

Calling this in handleAction using H.liftEffect (hide foo) works - the modal closes. However, a few seconds after that, I get this error on the console:

Uncaught TypeError: eff is not a function
    at runSync (index.js:1613)
    at _run (index.js:1613)
    at index.js:1613
    at drain (index.js:1613)
    at Object.enqueue (index.js:1613)
    at Object.run (index.js:1613)
    at __do (index.js:1613)
    at index.js:1613
    at index.js:1613
    at mbEmit (index.js:1613)

I’m not sure if this is related to my code. It doesn’t happen if I don’t open/close the modal at all.

What does the error tell me? I don’t even have the word eff in my code. The traceback is to Data.Map.Internal. It’s really confusing me.

I can provide more sample code, but I cannot publish the whole repository.

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#2

Effects in PureScript are represented in the compiled JS as functions that take no parameters. Thus, you would have to change the definition of hide to this:

exports.hide = modalId => () => {
    $('#'+modalId).modal("hide");
}

See https://github.com/purescript/documentation/blob/4f6c0e3b8b6184329ab1e9f7ec3c0f5a5e27a393/guides/FFI-Tips.md#why-doesnt-my-effect-work-when-passed-to-a-normal-js-function.

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#3

Excellent, thank you. Indeed it works now!

1 Like