purescript-justifill

This module provides three interesting functions: - fill Which adds Nothings to records with missing fields - justify Which turns non-Maybe values into Justs - and justifill which combines the two

Examples:

filled :: { name :: Maybe String, id :: Int }
filled = fill { id: 10 }
-- { name: Nothing, id: 10 }

justified :: { name :: Maybe String, age :: Maybe Int }
justified = justify { name: "Mark", age: 40 }
-- { name: Just "Mark", age: Just 40 }

justifilled :: { name :: Maybe String, age :: Maybe Int, id :: Int }
justifilled = justifill { name: "Mark", id: 12 }
-- { name: Just "Mark", age: Nothing, id: 12 }

Use cases

This can be handy when using APIs with many optional inputs (Props in React Components for example).

Combined with simple-json it can also be a viable alternative to something like purescript-options:

You can type your options as simple records with Maybes for non-mandatory fields:

foreign import someJSImpl :: Foreign -> Effect Unit

type SomeJSOptions =
  { option1 :: Maybe Int
  , option2 :: Maybe Number
  -- ...
  , option304 :: Maybe String
  , mandatory :: String }

someJS :: SomeJSOptions -> Effect Unit
someJS = write >>> someJSImpl

-- Usage:
result = someJS (justifill { mandatory: "Hi", option302: "Woah!" })