diff --git a/src/effects.ts b/src/effects.ts
index 2c495f6..f16ee41 100644
--- a/src/effects.ts
+++ b/src/effects.ts
@@ -10,28 +10,32 @@ export interface EffectMeta {
   seq?: number;
 }
 
-export interface Effect<P = any> {
+export interface Effect<P = unknown> {
   readonly type: EffectType;
   readonly payload: P;
   readonly meta: EffectMeta;
 }
 
-export interface EffectWithPayload<P> extends Effect<P> {
-  payload: P;
-}
+export type EffectWithPayload<P> = Effect<P>;
 
-export function createEffect<P>(type: EffectType, payload: P, meta: EffectMeta = {}): Effect<P> {
+export function createEffect<P>(
+  type: EffectType,
+  payload: P,
+  meta: EffectMeta = {}
+): EffectWithPayload<P> {
   return { type, payload, meta };
 }
 
 export interface TradeEffectPayload {
   readonly price: string;
-  readonly size: string; // TODO: Name?
+  readonly size: string;
   readonly side: TradeSide;
 }
 
-export interface TradeEffect extends EffectWithPayload<TradeEffectPayload> {}
+export type TradeEffect = EffectWithPayload<TradeEffectPayload>;
 
-export const tradeEffect = (payload: TradeEffectPayload) => createEffect(EffectType.Trade, payload);
+export const tradeEffect = (payload: TradeEffectPayload): TradeEffect =>
+  createEffect(EffectType.Trade, payload);
 
-export const isTradeEffect = (effect: Effect): effect is TradeEffect => effect.type === EffectType.Trade;
+export const isTradeEffect = (effect?: Effect): effect is TradeEffect =>
+  effect?.type === EffectType.Trade;