From 57a86f761605b6261d1045558c9cb7c83d723b60 Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <petermikkelsen10@gmail.com>
Date: Tue, 25 Jan 2022 19:28:31 +0000
Subject: =?UTF-8?q?Add=20under=20=E2=8D=A2=20and=20obverse=20=E2=8D=AB=20T?=
 =?UTF-8?q?each=20inverse()=20that=20the=20inverse=20of=20f=E2=8D=ABg=20is?=
 =?UTF-8?q?=20g=E2=8D=ABf=20=07?=
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---
 apl9.h      |  2 ++
 inverse.c   |  9 +++++++++
 operators.c | 23 ++++++++++++++++++++++-
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/apl9.h b/apl9.h
index 7c03918..b15b7e6 100644
--- a/apl9.h
+++ b/apl9.h
@@ -336,6 +336,8 @@ Array *opPower(Datum *, Datum *, Array *, Array *);
 Array *opBind(Datum *, Datum *, Array *, Array *);
 Array *opAtop(Datum *, Datum *, Array *, Array *);
 Array *opOver(Datum *, Datum *, Array *, Array *);
+Array *opUnder(Datum *, Datum *, Array *, Array *);
+Array *opObverse(Datum *, Datum *, Array *, Array *);
 Array *opSelfReference2(Datum *, Datum *, Array *, Array *);
 
 /* Dyadic functions from hybrids.c */
diff --git a/inverse.c b/inverse.c
index b37664b..c20e78d 100644
--- a/inverse.c
+++ b/inverse.c
@@ -7,6 +7,15 @@
 Function
 inverse(Function f)
 {
+	/* TODO figure out a good way to structure this code */
+	if(f.type == FunctypeOp && f.operator.type == OperatortypePrim && f.operator.code == 9 && f.operator.dyadic){
+		/* obverse */
+		Function newf = f;
+		newf.operator.left = f.operator.right;
+		newf.operator.right = f.operator.left;
+		return newf;
+	}
+
 	Rune *msg = runesmprint("No inverse defined for %S", ppfunction(f));
 	throwerror(msg, EDomain);
 	return f;
diff --git a/operators.c b/operators.c
index 1ecb8aa..2d26251 100644
--- a/operators.c
+++ b/operators.c
@@ -5,7 +5,7 @@
 #include "apl9.h"
 
 Rune primmonopnames[] = L"¨⍨⌸⌶&∆";
-Rune primdyadopnames[] = L"⍣.∘⍤⍥@⍠⌺⍙";
+Rune primdyadopnames[] = L"⍣.∘⍤⍥@⍠⌺⍢⍫⍙";
 
 opmonad monadoperatordefs[] = {
 	opEach, /* ¨ */
@@ -25,6 +25,8 @@ opdyad dyadoperatordefs[] = {
 	0, /* @ */
 	0, /* ⍠ */
 	0, /* ⌺ */
+	opUnder, /* ⍢ */
+	opObverse, /* ⍫ */
 	opSelfReference2, /* ⍙ */
 };
 
@@ -190,6 +192,25 @@ opAtop(Datum *lefto, Datum *righto, Array *left, Array *right)
 		return nil;
 }
 
+Array *
+opUnder(Datum *lefto, Datum *righto, Array *left, Array *right)
+{
+	if(lefto->tag != FunctionTag || righto->tag != FunctionTag)
+		throwerror(L"⍢ operands must be functions", EDomain);
+	if(left)
+		return rundfn(L"⍹⍣¯1 ⊢ (⍹ ⍺) ⍶ ⍹ ⍵", lefto, righto, left, right);
+	else
+		return rundfn(L"⍹⍣¯1 ⍶ ⍹ ⍵", lefto, righto, left, right);
+}
+
+Array *
+opObverse(Datum *lefto, Datum *righto, Array *left, Array *right)
+{
+	if(lefto->tag != FunctionTag || righto->tag != FunctionTag)
+		throwerror(L"⍫ operands must be functions", EDomain);
+	return runfunc(lefto->func, left, right);
+}
+
 Array *
 opOver(Datum *lefto, Datum *righto, Array *left, Array *right)
 {
-- 
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