oop-ffi

Utilities to convert JavaScript classes into FFI bindings for PureScript.

This tool does the following to you:

Generates the .purs and .js code;
Wraps multi-parameters functions with EffectFn_ and runEffectFn_;
Expose only the relevant binding functions (not the _Impl ones)
Optional properties are wrapped into Maybe;
Creates a typeclass for each class;
Extends typeclasses to preserve inheritance.

Declare how the foreign class looks like using JSON:

{
  "name": "Person",
  "namespace": "Person",
  "constructor": [ "String", "Int" ],
  "extends": [],
  "members": [
    { "name": "name", "required": true, "returns": "Unit" },
    { "name": "age", "required": true, "returns": "Int" }
  ],
  "methods": [
    { "name": "sayName", "args": [], "returns": "Unit" },
    { "name": "setAge", "args": [ "Int" ], "returns": "Person" }
  ]
}

Then, to generate the .purs and .js files: npx lfarroco/oop-ffi --path ./path/to/spec.json --output ./where_to_place_files/

You can also import this lib in PureScript and use generatePurs and generateJs to log to the files' contents to the console.

The files should look like this:

module Person where
(...)
foreign import data PersonInstance :: Type

class Person:: forall k. k -> Constraint
class Person a

instance Person PersonInstance

foreign import newPersonImpl :: EffectFn2 String Int PersonInstance

newPerson :: String -> Int -> Effect PersonInstance
newPerson = runEffectFn2 newPersonImpl
(...)

export const newPersonImpl = (a, b) =>
  new Person(a, b);

export const nameImpl = obj => obj.name;

export const ageImpl = obj => obj.age;

export const sayNameImpl = (obj) => obj.sayName();
(...)

Check /test for some examples of specs and generated files.

Inheritance

If you declare some class names in the extends field, the generated file will preserve the inheritance structure:

module Employee where
(...)
foreign import data EmployeeInstance :: Type

class Employee:: forall k. k -> Constraint
class (Person a) <= Employee a

instance Person EmployeeInstance
instance Employee EmployeeInstance

(...)

In the example above, an Employee can use all methods/members from Person.

Missing features:

Support for methods that return nullable values
Support for union types for arguments
Support for record arguments with optional properties