In Section 17.6 of Hull (9th global), it is said that "In some circumstances, it is optimal to exercise American currency and index options prior to maturity. Thus, American currency and index options are worth more than their European counterparts. In general, call options on high-interest currencies and put options on low-interest currencies are the most likely to be exercised prior to maturity. The reason is that a high-interest currency is expected to depreciate and a low-interest currency is expected to appreciate. Similarly, call options on indices with high-dividend yields and put options on indices with low-dividend yields are most likely to be exercised early." My understanding of the above is as below. Is it correct, please? "a high-interest currency is expected to depreciate" is due to covered interest rate parity; "call options on high-interest currencies ... the most likely to be exercised prior to maturity" means that once spot exchange rate is higher than the strike, then the call holder might want to exercise instead of waiting any longer since he/she expect the currency to depreciate on average. This leads to the early exercise.