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ffipurescript

How to map a 0-argument JavaScript function in PureScript FFI

I am trying to import the following JavaScript function into PureScript using the FFI:

function getGreeting() {
  return "Hi, welcome to the show."
}

but I am not sure what the type should be. The closest I get to is something like:

foreign import getGreeting :: Unit -> String

I do want getGreeting to stay a function, and not convert it to a constant.

Is there a better way to write the type? I tried to see what PureScript does if I define a dummy function in PureScript itself with that type of signature:

var getGreeting = function (v) {
  return "Hi, welcome to the show.";
};

Is there a way to get rid of that v parameter that is not being used?

TIA

Solution

  • Unit -> String is a perfectly good type for that, or perhaps forall a. a -> String. The latter type may seem too permissive, but we know for sure that the a is unused thanks to parametricity, so that the function still must be constant.