Add the key operator

2 files changed, 13 insertions, 1 deletions

diff --git a/apl9.h b/apl9.h
index cad5ae4..e33df18 100644
--- a/apl9.h
+++ b/apl9.h
@@ -367,6 +367,7 @@ Array *fnSelfReference2(Array *, Array *);
 /* Monadic operators from operators.c */
 Array *opEach(Datum *, Array *, Array *);
 Array *opSwitch(Datum *, Array *, Array *);
+Array *opKey(Datum *, Array *, Array *);
 Array *opOuterProduct(Datum *, Array *, Array *);
 Array *opSelfReference1(Datum *, Array *, Array *);
 
diff --git a/operators.c b/operators.c
index 8fd9911..202667c 100644
--- a/operators.c
+++ b/operators.c
@@ -10,7 +10,7 @@ Rune primdyadopnames[] = L"⍣.∘⍤⍥@⍠⌺⍢⍫⍙";
 opmonad monadoperatordefs[] = {
 	opEach, /* ¨ */
 	opSwitch, /* ⍨ */
-	0, /* ⌸ */
+	opKey, /* ⌸ */
 	0, /* ⌶ */
 	0, /* & */
 	opOuterProduct, /* ⌾ */
@@ -80,6 +80,17 @@ opSwitch(Datum *lefto, Array *left, Array *right)
 }
 
 Array *
+opKey(Datum *lefto, Array *left, Array *right)
+{
+	if(lefto->tag != FunctionTag)
+		throwerror(nil, EType);
+	if(left)
+		return rundfn(L"↑⍵∘(⍶{⍵⍶⍺⌷⍨⊂⍸⍹≡¨⍵}⍺)¨⊂¨∪⍺", lefto, nil, left, right);
+	else
+		return rundfn(L"⍵⍶⌸⍳≢⍵", lefto, nil, left, right);
+}
+
+Array *
 opOuterProduct(Datum *lefto, Array *left, Array *right)
 {
 	if(left == nil)