diff --git a/src/index.ts b/src/index.ts
index d22695b..6936026 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,43 +1,43 @@
-type EventShape = [name:string, payload:any];
-export interface Machine_T<S,E extends EventShape> {
-  states: Array<State_T<S,E>>
+type Event_T = [name:string, payload:any];
+export interface Machine_T<S,E extends Event_T,C> {
+  states: Array<State_T<S,E,C>>
 }
-export interface State_T<S,E extends EventShape> {
+export interface State_T<S,E extends Event_T,C> {
   name: S;
-  ons: Array<On_T<S,E>>;
+  ons: Array<On_T<S,E,C>>;
 }
-export interface On_T<S,E extends EventShape> {
+export interface On_T<S,E extends Event_T,C> {
   eventName: E[0];
-  reactions: Array<Do_T | Goto_T<S>>;
+  reactions: Array<Do_T<E,C> | Goto_T<S>>;
 };
-export interface Do_T {
+export interface Do_T<E extends Event_T, C> {
   type: 'Do';
-  fn: DoFn_T;
+  fn: DoFn_T<E,C>;
 };
-export type DoFn_T = (ctx,e,self)=>any;
+export type DoFn_T<E extends Event_T, C> = (ctx:C,e:E,self)=>any;
 export interface Goto_T<S> {
   type: 'Goto';
   targetStateName: S;
 };
 
-export const Machine = function<S,E extends EventShape>(...states:Array<State_T<S,E>>) : Machine_T<S,E> { return {states}; };
-export const State = function<S,E extends EventShape>(name:S, ...ons:Array<On_T<S,E>>) : State_T<S,E>{ return {name, ons}; };
-export const On = function<S,E extends EventShape>(eventName:E[0], ...reactions:Array<Do_T | Goto_T<S>>) : On_T<S,E>{ return {eventName, reactions}; };
-export const Do = function(fn:DoFn_T) : Do_T{ return {type:'Do', fn}; };
+export const Machine = function<S,E extends Event_T,C>(...states:Array<State_T<S,E,C>>) : Machine_T<S,E,C> { return {states}; };
+export const State = function<S,E extends Event_T,C>(name:S, ...ons:Array<On_T<S,E,C>>) : State_T<S,E,C>{ return {name, ons}; };
+export const On = function<S,E extends Event_T,C>(eventName:E[0], ...reactions:Array<Do_T<E,C> | Goto_T<S>>) : On_T<S,E,C>{ return {eventName, reactions}; };
+export const Do = function<E extends Event_T, C>(fn:DoFn_T<E,C>) : Do_T<E,C>{ return {type:'Do', fn}; };
 export const Goto = function<S>(targetStateName:S) : Goto_T<S> { return {type:'Goto', targetStateName} };
 
-interface Tick_T {
-  doFunctions: Array<DoFn_T>
+interface Tick_T<E extends Event_T, C> {
+  doFunctions: Array<DoFn_T<E,C>>
 };
-const Tick = function(doFunctions : Array<DoFn_T>) : Tick_T{ return {doFunctions}; };
+const Tick = function<E extends Event_T,C>(doFunctions : Array<DoFn_T<E,C>>) : Tick_T<E,C>{ return {doFunctions}; };
 
 
-export interface Interpreter_T<S,E extends EventShape,C> {
-  machine: Machine_T<S,E>;
+export interface Interpreter_T<S,E extends Event_T,C> {
+  machine: Machine_T<S,E,C>;
   state: S;
   context: C | {};
 }
-export function interpret<S,E extends EventShape,C>(machine:Machine_T<S,E>, options?:{state?:S, context?:C | {}}) : Interpreter_T<S,E,C>{
+export function interpret<S,E extends Event_T,C>(machine:Machine_T<S,E,C>, options?:{state?:S, context?:C | {}}) : Interpreter_T<S,E,C>{
   let {state, context} = options || {};
   if(typeof state === 'undefined'){ state = machine.states[0].name; }
   if(typeof context === 'undefined'){ context = {}; }
@@ -46,12 +46,12 @@ export function interpret<S,E extends EventShape,C>(machine:Machine_T<S,E>, opti
 
 /**  Helper function for `send()`
  */
-function getState<S,E extends EventShape,C>(interpreter : Interpreter_T<S,E,C>) : State_T<S,E>{
-  return interpreter.machine.states.find((state)=>state.name===interpreter.state) as unknown as State_T<S,E>;
+function getState<S,E extends Event_T,C>(interpreter : Interpreter_T<S,E,C>) : State_T<S,E,C>{
+  return interpreter.machine.states.find((state)=>state.name===interpreter.state) as unknown as State_T<S,E,C>;
 }
 /**  Helper function for `send()`
  */
-function getOns<S,E extends EventShape>(state : State_T<S,E>, event:E) : Array<On_T<S,E>>{
+function getOns<S,E extends Event_T,C>(state : State_T<S,E,C>, event:E) : Array<On_T<S,E,C>>{
   return state.ons.filter((on)=>on.eventName===event[0]);
 }
 /**  Inject an Event into the Interpreter's "tick queue".
@@ -64,7 +64,7 @@ function getOns<S,E extends EventShape>(state : State_T<S,E>, event:E) : Array<O
  * whether to run a reaction at all. If an Event is received, and is specified to be applied on a past 
  * Tick, it is discarded.
  */
-export function send<S,E extends EventShape,C>(interpreter : Interpreter_T<S,E,C>, event:E){
+export function send<S,E extends Event_T,C>(interpreter : Interpreter_T<S,E,C>, event:E){
   const state = getState(interpreter);
   const ons = getOns(state, event);
   const tick = Tick(ons
@@ -75,10 +75,10 @@ export function send<S,E extends EventShape,C>(interpreter : Interpreter_T<S,E,C
           return reaction.fn;
         }
         else if(reaction.type === 'Goto'){
-          return (ctx,e,self)=>{};
+          return (ctx:C,e:E,self)=>{};
         }
         else{
-          return (ctx,e,self)=>{};
+          return (ctx:C,e:E,self)=>{};
         }
       })
   );
diff --git a/src/tests/00-basic.ts b/src/tests/00-basic.ts
index bf445e4..74ac08c 100644
--- a/src/tests/00-basic.ts
+++ b/src/tests/00-basic.ts
@@ -1,12 +1,13 @@
 import { Machine, State, On, Do, Goto, Spawn, Unspawn } from '../index';
 
-const beginTimer = ()=>{};
+const beginTimer = (ctx:C, e:E)=>{};
 
 type S = 'green' | 'yellow' | 'red';
 type E = ['entry',null] | ['timer-finished',null];
+type C = null;
 
 const machine = 
-  Machine<S,E>(
+  Machine<S,E,C>(
     State('green',
       On('entry', 
         Do(beginTimer)