FEAT: reduce paren! evaluate and generate paren!

resolves: Oldes/Rebol-issues#2060

Author: Oldes

src/core/n-control.c

@@ -742,7 +742,7 @@ enum {
 	REBVAL *val = D_ARG(1);
 	REBVAL *into = D_REF(5) ? D_ARG(6) : 0;
 
-	if (IS_BLOCK(val)) {
+	if (IS_BLOCK(val) || IS_PAREN(val)) {
 		REBSER *ser = VAL_SERIES(val);
 		REBCNT index = VAL_INDEX(val);
 
@@ -752,6 +752,10 @@ enum {
 			Reduce_Only(ser, index, D_ARG(4), into);
 		else
 			Reduce_Block(ser, index, into);
+
+		if(!into)
+			SET_TYPE(DS_TOP, VAL_TYPE(val));
+
 		return R_TOS;
 	}
 	else if (into != 0) {

src/tests/units/series-test.r3

@@ -288,6 +288,32 @@ Rebol [
 ===end-group===
 
 
+===start-group=== "REDUCE"
+	--test-- "reduce block!"
+		--assert [2 6] == reduce [1 + 1 3 + 3]
+		--assert all [
+			[x] == reduce/into [1 + 1 3 + 3] b: [x]
+			b = [2 6 x]
+		]
+		--assert all [
+			tail? reduce/into ['a 1 + 1 3 + 3] p: make path! 3
+			p = 'a/2/6
+		]
+	--test-- "reduce paren!"
+	;@@ https://github.com/Oldes/Rebol-issues/issues/2060
+		--assert 2 = reduce (1 + 1)
+		--assert quote (2 6) == reduce quote (1 + 1 3 + 3)
+		--assert all [
+			[x] == reduce/into quote (1 + 1 3 + 3) b: [x]
+			b = [2 6 x]
+		]
+		--assert all [
+			tail? reduce/into quote ('a 1 + 1 3 + 3) p: make path! 3
+			p = 'a/2/6
+		]
+===end-group===
+
+
 ===start-group=== "TRIM"
 	--test-- "trim string!"
 		str1: " a b c "