feat: 🎸 add updateSpread operator

index.js

@@ -25,6 +25,16 @@ exports.curryGroupsN = n => f => {
  */
 exports.update = reducer => state => (...vals) => {state = reducer(state, ...vals); return state}
 
+/**
+ * Same as `update` but spread return values of curried reducer.
+ * This allows to update tuples rather than single values as `update` does.
+ * Reducer is curried for clean separation of arguments.
+ * As JavaScript has no tuples, use arrays instead.
+ * 
+ * @param {Function} reducer: (s0,...,sn) -> (x0,...,xm) -> (s0,...,sn)
+ * @returns {Function} updateSpread(reducer): (s0,...,sn) -> (x0,...,xn) -> reducer(s0,...,sn)(x0,...,xm)
+ */
+exports.updateSpread = reducer => (...state) => (...vals) => {state = reducer(...state)(...vals); return state}
 
 /**
  * Pass tuple of values to sequence of functions similar to UNIX pipe

test/update.test.js

@@ -1,15 +1,15 @@
 const test = require('./config')
 const { update } = require('..')
 
-test('update transforms simple reducer to updateulator', t=>{
+test('update transforms simple reducer to updater', t=>{
 	const add = update((state,v)=>state+v)(10)
 	t.is(add(1),10+1)
 	t.is(add(2),10+1+2)
 	t.is(add(-1),10+1+2-1)
 })
 
 test('update works with reducer with variadic tuples of values', t=>{
-	const concat = update((arr, ...rest)=>arr.concat(rest))([0])
+	const concat = update((arr, ...rest) => [...arr, ...rest])([0])
 	t.deepEqual(concat(1),[0,1])
 	t.deepEqual(concat(),[0,1])
 	t.deepEqual(concat(1,2,3),[0,1,1,2,3])

test/updateSpread.test.js

@@ -0,0 +1,16 @@
+const test = require('./config')
+const { updateSpread } = require('..')
+
+test('updateSpread transforms simple curried reducer that returns array', t=>{
+	const add = updateSpread(state => v =>[state+v])(10)
+	t.deepEqual(add(1),[10+1])
+	t.deepEqual(add(2),[10+1+2])
+	t.deepEqual(add(-1),[10+1+2-1])
+})
+
+test('updateSpread works with curried reducer with variadic tuples of values', t=>{
+	const concat = updateSpread((...arr) => (...vals) => [...arr, ...vals])(0,0)
+	t.deepEqual(concat(1),[0,0,1])
+	t.deepEqual(concat(),[0,0,1])
+	t.deepEqual(concat(1,2,3),[0,0,1,1,2,3])
+})