Add Range method to iterate through Value tree

This adds a Range function for walking the AST depth-first and
applying a custom function to each leaf

format.go

@@ -88,6 +88,21 @@ func (v *Value) Format() {
  v.UpdateOffsets()
 }
 
+// Range iterates through a Value in depth-first order and
+// calls f for each value (including the root value).
+// It stops iteration when f returns false.
+func (v *Value) Range(f func(v *Value) bool) bool {
+ if !f(v) {
+ return false
+ }
+ if comp, ok := v.Value.(composite); ok {
+ return comp.rangeValues(func(v2 *Value) bool {
+ return v2.Range(f)
+ })
+ }
+ return true
+}
+
 // normalize performs simple normalization changes. In particular, it:
 // - normalizes strings,
 // - normalizes empty objects and arrays as simply {} or [],
@@ -98,7 +113,7 @@ func (v *Value) Format() {
 func (v *Value) normalize() bool {
  switch v2 := v.Value.(type) {
  case Literal:
- // Format string.
+ // Normalize string if there are escape characters.
  if v2.Kind() == '"' && bytes.IndexByte(v2, '\\') >= 0 {
  v.Value = String(v2.String())
  }