// Product-type (also called: pair, tuple)

// A Product-type always has only two fields, called "left" and "right".
// Product-types of more fields (called Structs) can be constructed by nesting Product-types.

import { makeGeneric } from "../generics/generics.js";
import { GenericType, Type } from "../primitives/types.js";
import { typedFnType } from "./types.js";
import { prodType } from "./types.js";

// In JS, all products are encoded in the same way:
export const constructorProduct = l => r => ({l, r});
export const getLeft     = product => product.l;
export const getRight    = product => product.r;

export const ModuleProduct = {l: [
  // binary type constructor
  // Type -> Type -> Type
  ...typedFnType(prodType, fnType =>
    fnType
      (Type)
      (fnType
        (Type)
        (Type)
      )
  ),

  // a -> b -> (a, b)
  ...typedFnType(constructorProduct, fnType =>
    makeGeneric((a, b) =>
      fnType
        (a)
        (fnType
          (b)
          (prodType(a)(b))
        )
    ), GenericType),

  // (a, b) -> a
  ...typedFnType(getLeft, fnType =>
    makeGeneric((a, b) =>
      fnType
        (prodType(a)(b))
        (a)
    ), GenericType),

  // (a, b) -> b
  ...typedFnType(getRight, fnType =>
    makeGeneric((a, b) =>
      fnType
        (prodType(a)(b))
        (b)
    ), GenericType),
]};