From fd5007d0e5ff97acfddc6d60425f567b8d95dbe5 Mon Sep 17 00:00:00 2001
From: Marshall Lochbaum <mwlochbaum@gmail.com>
Date: Mon, 11 Jan 2021 22:06:22 -0500
Subject: Create expandable index for structural Under

---
 src/r.bqn | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/r.bqn b/src/r.bqn
index 5fd2e620..b9d716ef 100644
--- a/src/r.bqn
+++ b/src/r.bqn
@@ -714,5 +714,15 @@ Inverse ← Type◶(3‿1‿2/{⊢⊣𝕩IX∘≡⊢}‿FuncInverse‿("Cannot i
 ⁼ ↩ {𝕗 (≢∧INF˙⊸≢)◶0‿(5‿_inv_≢0‿¯2⊏Decompose∘⊢)◶⊢‿{𝕏_inv_(𝕎_invChk_𝕏)} Inverse 𝕗}
 
 _structural←{
-  ⟨⟩‿(𝔽⥊⟜(↕1×´⊢)≢𝕩)
+  Inds ← ⥊⟜(↕1×´⊢)∘≢ 𝕩⊑⟜⥊´⌽
+  _s_ ← {
+    f←𝕗
+    st‿d‿o←𝕩
+    g←𝕨 St Inds∘{f↩f(¯1≢⊣)◶⟨⟩‿∾𝕩}⍟(d>IsArray) 𝕘
+    {f _s_ 𝕩}⍟o g
+  }
+  IsStruct ← 5‿s ≡ 0‿¯2⊏Decompose
+  _sfn ← {(IsStruct⊢)◶⟨𝕏, 𝕩‿𝕨‿𝕗{𝕨𝕏𝕗}⟩}
+  Depth←1 _sfn ⋄ Info←0 _sfn
+  1‿3 ⊏ Decompose {𝕎𝕩}´ ⟨1 Depth 𝕗, ¯1 _s_ 0⟩
 }
-- 
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