// transform replaces each node in a regex AST with the return value of the given function
// it processes the children of a node before the node itself
func transform(expr *syntax.Regexp, f transformer) (*syntax.Regexp, error) {
var newchildren []*syntax.Regexp
for _, child := range expr.Sub {
newchild, err := transform(child, f)
if err != nil {
return nil, err
}
replacements, err := f(newchild)
if err != nil {
return nil, err
}
newchildren = append(newchildren, replacements...)
}
expr.Sub = newchildren
return expr, nil
}
