In a tall glass, combine simple syrup, tamarind purée, mango pulp and lime juice and stir well. Add ice, rum (if using) and ginger beer. Garnish with a lime wedge and serve.
Notes
To make simple syrup, combine sugar and ¾ cup water in a small saucepan over medium heat. Heat for 1 to 2 minutes, until sugar has completely dissolved. Pour into a container and set aside to cool.