Syntax for polymorphic record type alias

2
votes

Is there a way to define a type/alias representing a row polymorphic record?

So given this example

tester :: forall r. {val :: Int | r} -> Int
tester a =
  a.val

callTester = tester {val: 1, b: 2}

I want to define the record type as an alias. Something like

type Val = forall r. {val :: Int | r}

tester :: Val -> Int 
tester a =
  a.val

callTester = tester {val: 1, b: 2}

But that will not compile.

For larger records and more complex functions defining the types multiple times leads to quite a lot of noise. It would be nice to factor this out. e.g. fn :: a -> b -> a I have to define a twice

For non-polymorphic records its simple but I explicitly want to allow records with additional fields that are not know upfront.

Thanks

1
purescript

1 Answers

4
votes

Here is how I got it working for the example above. 

type Val r = {val :: Int | r}

tester :: forall a. Val a -> Int
tester v =
  v.a

callTester = tester {val: 1, b: 2}

So define a type, and have the forall on the functions using the type