Yes! Syntactically Purescript essentially automatically gives you lightweight lenses for records. E.g. myValue { field0 { subField0 { subSubField0 = 5 }}} S

Yes! Syntactically Purescript essentially automatically gives you lightweight lenses for records. E.g. myValue { field0 { subField0 { subSubField0 = 5 }}} Semantically... oh boy, row types (i.e. extensible product types) and polymorphic variants (i.e. extensible sum types) are fantastic! I'd go so far as to say as long as you give me `newtype`, I would be in favor of row types and polymorphic variants completely replacing `data` declarations. -- forall x here means that our record can have other fields resetName :: forall x. { name :: String | x } -> { name :: String | x } resetName itemWithName = itemWithName { name = "Default" } -- Notice how Person is just a type synonym! -- And there's no data constructor -- { name :: String, id :: Int } is a type, not just a constructor type Person = { name :: String, id :: Int } type Pet = { name :: String, owner :: Person } bob = { name : "Bob", id : 0 } doggy = { name : "Doggy", owner : bob } -- Look they both work! bobReset = resetName bob doggyReset = resetName doggy -- And no clashes, because records are a first class type declaration bob.name == "Bob" doggyReset.name == "Default" Purescript unfortunately doesn't have built-in polymorphic variants (you can derive them from row types with a bit of type-level hackery), so a bit of this is pseudo-Purescript (mainly the case declaration, functionally you can get the same thing, it just looks slightly different). newtype TextTooShort = ... newtype TextNotValidASCII = ... findFirst5CharWord :: forall e. String -> Either (TextTooShort + e) String asciiNumberRepresentation :: forall e. String -> Either (TextNotValidASCII + e) (Array Int) processString :: forall e. String -> Either (TextTooShort + TextNotValidASCII + e) (Array Int) -- No lifting or wrapping of intermediate errors required! -- All the types still unify! processString = findFirst5CharWord `andThen` asciiNumberRepresentation -- But you still get exhaustivity checking! displayString :: String -> String displayString input = case (processString input) of Left TextTooShort -> "You didn't give me enough text!" Left TextNotValidAscii -> "Whoops no ASCII rep exists!" Right arrayOfInts -> show arrayOfInts