iter-ops raised above assign; 'cat' operator returns an iterator; $$ operator supports iterators producing a list of items

scan/symbol-map.go

@@ -138,6 +138,7 @@ func init() {
 		SymKwMap:     {"map", SymClassOperator, PosInfix},
 		SymKwFilter:  {"filter", SymClassOperator, PosInfix},
 		SymKwDigest:  {"digest", SymClassOperator, PosInfix},
+		SymKwCat:     {"cat", SymClassOperator, PosInfix},
 		SymKwJoin:    {"join", SymClassOperator, PosInfix},
 		SymKwGroupBy: {"groupby", SymClassOperator, PosInfix},
 		SymKwFunc:    {"func(", SymClassDeclaration, PosPrefix},

scan/term.go

@@ -15,9 +15,9 @@ type TermPriority uint32
 const (
 	PriNone TermPriority = iota
 	PriRange
-	PriIterOp // map, filter, digest, etc
 	PriBut
 	PriAssign
+	PriIterOp // map, filter, digest, etc
 	PriInsert
 	PriOr
 	PriAnd