code: func RegisterBuiltin(b *Builtin) {
  	Builtins = append(Builtins, b)
  	BuiltinMap[b.Name] = b
  	if len(b.Infix) > 0 {
  		BuiltinMap[b.Infix] = b
  	}
  }
docs: // RegisterBuiltin adds a new built-in function to the registry.