IAmNeil

Supply and demand for currency are affected by the same factors but in opposite ways. The net affect of any change, is the price will increase or decrease, but the quantity supplied will stay the same. Visualize a Supply and Demand graph in the following graph.
For instance, if real rate increases, foreign demand for the currency shifts to the right. At the same time though, the amount people are willing to supply decrease because they want to invest in the higher domestic real rate. So the supply curve shifts to the left. The net affect, is the price of the currency increases, but the shift to the right in demand and the shift to the left in supply, offset each other and the equilibrium quantity remains unchanged.