tag : break apart into smaller files of related function

tag/set.go

@@ -0,0 +1,37 @@
+package tag
+
+import (
+	"maps"
+	"slices"
+)
+
+// convenience shorthand for this awkward map type.
+type Set map[string]bool
+
+// add members to the "set"
+func (s Set) Add(mems ...string) {
+	for _, m := range mems {
+		s[m] = true
+	}
+}
+
+// get all members in a slice
+func (s Set) Members() []string {
+	return slices.Collect(maps.Keys(s))
+}
+
+// s ∪ t
+func (s Set) Union(tt ...Set) {
+	for _, t := range tt {
+		s.Add(t.Members()...)
+	}
+}
+
+// s ∩ t
+func (s Set) Intersect(t Set) {
+	for m, _ := range s {
+		if !t[m] {
+			delete(s, m)
+		}
+	}
+}