Functional Example in JS

conn.js

function new = () => ({
  _struct: "Conn",
  host: null,
  path: null,
  port: null,
  scheme: null,
  params: {},
  requestHeaders: [],
  responseHeaders: [],
  responseBody: {},
  status: null
})

function putHost = (conn, host) => ({...user, name: name})

function putRequestHeaders = (conn, ...headers) => ({...conn, requestHeaders: [...conn.requestHeaders, ...headers})

function putPath = (conn, path) => ({...conn, path: path})

function putPort = (conn, port) => ({...conn, port: port})

function putScheme = (conn, scheme) => ({...conn, scheme: scheme})

function putParams = (conn, params) => ({...conn, params: params})

function putStatus = (conn, status) => ({...conn, status: status})

function putResponseHeaders = (conn, ...headers) => ({...conn, responseHeaders: [...conn.responseHeaders, ...headers]})

function putResponseBody = (conn, body) => ({...conn, responseBody: body})

function getHost = (conn) => conn.host

function getPath = (conn) => conn.path

function getPort = (conn) => conn.port

function getScheme = (conn) => conn.scheme

function getParams = (conn) => conn.params

function getStatus = (conn) => conn.status

function getRequestHeaders = (conn) => conn.requestHeaders.reduce((acc, [key, val]) => ({...acc, [key]: val}), {})

function getResponseHeaders = (conn) => conn.responseHeaders.reduce((acc, [key, val]) => ({...acc, [key]: val}), {})

function getResponseBody = (conn) => conn.responseBody

export default {
  new,
  putHost,
  putPath,
  putPort,
  putScheme,
  putParams,
  putRequestHeaders,
  putResponseHeaders,
  putResponseBody,
  putStatus,
  getHost,
  getPath,
  getPort,
  getScheme,
  getParams,
  getStatus,
  getRequestHeaders,
  getResponseHeaders,
  getResponseBody
}

users_controller.js

import Conn from './conn.js'
import User from './user.js' // some schema/model to help map to user from DB

function show(conn) {
  render(conn, User.getBy({id: Conn.getParams(conn)["id"]})
}

function render(conn, body) {
  conn = putStatus(conn, 200)
  conn = putResponseHeaders(conn, ["Content-Type", "application/json"])
  return putResponseBody(conn, JSON.stringify(body))
}