From 12e1d1fe6464964b2bee1b83b8524445fc2bbe2c Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <petermikkelsen10@gmail.com>
Date: Fri, 21 Jan 2022 22:37:18 +0000
Subject: =?UTF-8?q?Implement=20scans=20=E2=8D=80=20and=20\?=
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---
 apl9.h    |  2 ++
 hybrids.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/apl9.h b/apl9.h
index 6e6574e..92a5127 100644
--- a/apl9.h
+++ b/apl9.h
@@ -274,7 +274,9 @@ Array *opOver(Datum *, Datum *, Array *, Array *);
 
 /* Monadic operators from hybrids.c */
 Array *opReduceLast(Datum *, Array *, Array *);
+Array *opScanLast(Datum *, Array *, Array *);
 Array *opReduceFirst(Datum *, Array *, Array *);
+Array *opScanFirst(Datum *, Array *, Array *);
 
 /* Global variables */
 extern int traceeval; /* eval.c */
diff --git a/hybrids.c b/hybrids.c
index 39f3f7a..00977da 100644
--- a/hybrids.c
+++ b/hybrids.c
@@ -15,9 +15,9 @@ fndyad hybridfunctiondefs[] = {
 
 opmonad hybridoperatordefs[] = {
 	opReduceLast, /* / */
-	0, /* \ */
+	opScanLast, /* \ */
 	opReduceFirst, /* ⌿ */
-	0, /* ⍀ */
+	opScanFirst, /* ⍀ */
 };
 
 /* function definitions */
@@ -37,6 +37,20 @@ opReduceLast(Datum *lefto, Array *left, Array *right)
 	return res;
 }
 
+Array *
+opScanLast(Datum *lefto, Array *left, Array *right)
+{
+	if(left)
+		throwerror(L"f\ doesn't take a left argument", ESyntax);
+
+	right = fnTranspose(right);
+	Array *tmp = opScanFirst(lefto, left, right);
+	Array *res = fnTranspose(tmp);
+	freearray(right);
+	freearray(tmp);
+	return res;
+}
+
 Array *
 opReduceFirst(Datum *lefto, Array *left, Array *right)
 {
@@ -80,5 +94,35 @@ opReduceFirst(Datum *lefto, Array *left, Array *right)
 		index->arraydata[index->size-1]->intdata[0]++;
 	}
 	freearray(index);
+
 	return result;
 }
+
+Array *
+opScanFirst(Datum *lefto, Array *left, Array *right)
+{
+	if(left)
+		throwerror(L"f⍀ doesn't take a left argument", ESyntax);
+
+	Array *result = allocarray(AtypeArray, right->rank, right->size);
+	for(int i = 0; i < right->rank; i++)
+		result->shape[i] = right->shape[i];
+
+	int n = result->shape[0];
+	int m = result->size / n;
+	for(int i = 0; i < n; i++){
+		Array *len = mkscalarint(i + 1);
+		Array *index = fnIndexGenerator(len);
+		Array *ix = fnEnclose(index);
+		Array *subarr = fnIndex(ix, right);
+		Array *subres = opReduceFirst(lefto, left, subarr);
+		for(int j = 0; j < m; j++)
+			result->arraydata[i*m + j] = arrayitem(subres, j);
+		freearray(len);
+		freearray(index);
+		freearray(ix);
+		freearray(subarr);
+		freearray(subres);
+	}
+	return result;
+}
\ No newline at end of file
-- 
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