/**
  Modular function type
*/
{ config, lib, ... }:
let
  inherit (lib) mkOption types;
  inherit (types)
    submodule
    functionTo
    optionType
    ;
in
{
  options = {
    input-type = mkOption {
      type = optionType;
    };
    output-type = mkOption {
      type = optionType;
    };
    function-type = mkOption {
      type = optionType;
      readOnly = true;
      default = functionTo config.output-type;
    };
    wrapper-type = mkOption {
      type = optionType;
      readOnly = true;
      default = functionTo (submodule {
        options = {
          input = mkOption {
            type = config.input-type;
          };
          output = mkOption {
            type = config.output-type;
          };
        };
      });
    };
    implementation = mkOption {
      type = config.function-type;
      default = _: { };
    };
    wrapper = mkOption {
      type = config.wrapper-type;
      readOnly = true;
      default = input: fn: {
        inherit input;
        output = config.implementation fn.config.input;
      };
    };
    apply = mkOption {
      type = config.function-type;
      readOnly = true;
      default = input: (config.wrapper input).output;
    };
  };
}