FIX: UNIQUE/DIFFERENCE/INTERSECT/UNION/EXCLUDE do not accept some data types

fixes: Oldes/Rebol-issues#1765

Author: Oldes

src/core/t-map.c

@@ -128,7 +128,9 @@
 	// Compute hash for value:
 	len = hser->tail;
 	hash = Hash_Value(key, len);
-	if (!hash) Trap_Type(key);
+	//o: use fallback hash value, if key is not a hashable type, instead of an error
+	//o: https://github.com/Oldes/Rebol-issues/issues/1765
+	if (!hash) hash = 3 * (len/5); //Trap_Type(key);
 
 	// Determine skip and first index:
 	skip  = (len == 0) ? 0 : (hash & 0x0000FFFF) % len;

src/tests/units/series-test.r3

@@ -1345,6 +1345,20 @@ Rebol [
 
 ===end-group===
 
+===start-group=== "More set operations"	
+--test-- "unhashable types"
+	;@@ https://github.com/Oldes/Rebol-issues/issues/1765
+	blk1: reduce ["a" [1 2 3] 'path/path func [][] charset ["a"]]
+	blk2: append copy blk1 blk1
+	--assert blk1 = unique blk2
+	--assert blk1 = union blk1 blk2 
+	append blk2 blk3: ["b" [3 4]]
+	--assert blk1 = intersect  blk2 blk1
+	--assert blk3 = difference blk1 blk2
+	--assert blk3 = exclude blk2 blk1
+	--assert empty? exclude blk1 blk2
+===end-group===
+
 ===start-group=== "TO-*"
 
 --test-- "to-path"