import { DefaultMap } from "../util.js";

const symbolFunction = Symbol('Function');

// The registry ensures that we never accidentally create more than one JS object for the same function type.
// It is a cheap workaround for JS lacking customizable hash-functions and equality-testing-functions.
// This same pattern is repeated throughout the code for all non-nullary type constructors (list, sum, product, ...)
const fnTypeRegistry = new DefaultMap(inType => new DefaultMap(outType => ({
  symbol: symbolFunction,
  params: [inType, outType],
})));

// type constructor for function types
export const fnType = inType => outType => fnTypeRegistry.getdefault(inType, true).getdefault(outType, true);


// Wrapper around function below.
export const typedFnType = (instance, callback) => {
  const [t, typesOfFns] = typedFnType2(callback);
  const res = [
    { i: instance, t },
    ...typesOfFns,
  ];
  return res;
};
// Create a function type, and also create Type-links for the function type (being typed by Function) and for all the nested function types. Saves a lot of code writing.
export const typedFnType2 = callback => {
  const fnTs = [];
  const wrappedFnType = ({ in: inType, out: outType }) => {
    const fnT = fnType({ in: inType, out: outType });
    fnTs.push(fnT);
    return fnT;
  };
  const t = callback(wrappedFnType); // force evaluation
  return [
    t,
    fnTs.map(fnT => ({ i: fnT, t: Function })),
  ];
};


export const ModuleFunction = {l:[
  // binary type constructor: Type -> Type -> Type
  ...typedFnType(fnType, fnType => fnType
    /* in  */ (Type)
    /* out */ (fnType
      /* in  */ (Type)
      /* out */ (Type)
    )
  ),
]};