From 29bdfb2d90637a4c0ae618efa4b0a9f315263b70 Mon Sep 17 00:00:00 2001
From: alex <alex@slab.org>
Date: Fri, 25 Feb 2022 11:19:12 +0000
Subject: [PATCH] _withContext()

---
 strudel.mjs           |  4 ++++
 test/pattern.test.mjs | 13 +++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/strudel.mjs b/strudel.mjs
index 044b7123..9d90bc57 100644
--- a/strudel.mjs
+++ b/strudel.mjs
@@ -312,6 +312,10 @@ class Pattern {
         return this._withEvent(event => event.setContext(context))
     }
 
+    _withContext(func) {
+        return this._withEvent(event => event.setContext(func(event.context)))
+    }
+
     withLocation(location) {
       return this.fmap(value => {
         value = typeof value === 'object' && !Array.isArray(value) ? value : { value };
diff --git a/test/pattern.test.mjs b/test/pattern.test.mjs
index ae950321..5154ed86 100644
--- a/test/pattern.test.mjs
+++ b/test/pattern.test.mjs
@@ -353,6 +353,19 @@ describe('Pattern', function() {
       )
     })
   })
+  describe('_withContext()', () => {
+    it('Can update the event context', () => {
+      assert.deepStrictEqual(
+        pure("a")._setContext([[[0,1],[1,2]]])._withContext(c => [...c,[[3,4],[3,4]]]).firstCycle,
+        [hap(ts(0,1),
+             ts(0,1), 
+             "a", 
+             [[[0,1],[1,2]],[[3,4],[3,4]]]
+            )
+        ]
+      )
+    })
+  })
   describe("apply", () => {
     it('Can apply a function', () => {
       assert.deepStrictEqual(