From 9df20fcbc5f9d2ef01ac90010427c8baca3f461a Mon Sep 17 00:00:00 2001
From: alex <alex@slab.org>
Date: Sat, 23 Apr 2022 09:38:05 +0100
Subject: [PATCH] support `cat`ting subpatterns, fixes #87

---
 packages/core/pattern.mjs           | 5 ++++-
 packages/core/test/pattern.test.mjs | 6 ++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/packages/core/pattern.mjs b/packages/core/pattern.mjs
index 3662b405..4c8df71d 100644
--- a/packages/core/pattern.mjs
+++ b/packages/core/pattern.mjs
@@ -837,7 +837,10 @@ export function stack(...pats) {
 export function slowcat(...pats) {
   // Concatenation: combines a list of patterns, switching between them
   // successively, one per cycle.
-  pats = pats.map(reify);
+
+  // Array test here is to avoid infinite recursions..
+  pats = pats.map(pat => Array.isArray(pat) ? sequence(...pat) : reify(pat));
+
   const query = function (state) {
     const span = state.span;
     const pat_n = mod(span.begin.sam(), pats.length);
diff --git a/packages/core/test/pattern.test.mjs b/packages/core/test/pattern.test.mjs
index 1c60766a..17385c78 100644
--- a/packages/core/test/pattern.test.mjs
+++ b/packages/core/test/pattern.test.mjs
@@ -413,6 +413,12 @@ describe('Pattern', function () {
         ['c'],
       );
     });
+    it ('Can cat subpatterns', () => {
+      sameFirst(
+        slowcat('a', ['b','c']).fast(4),
+        sequence('a', ['b', 'c']).fast(2)
+      )
+    })
   });
   describe('rev()', function () {
     it('Can reverse things', function () {