Cirrus cloud spreading from the top of a dying cumulonimbus. Cirrus forms from tropical cyclones, and is commonly seen fanning out from the eyewalls of hurricanes. A large shield of cirrus and cirrostratus typically accompanies the high altitude outflow of hurricanes or typhoons, and these can make the underlying rain bands—and sometimes even the eye—difficult to detect in satellite photographs. Thunderstorms can form dense cirrus at their tops. As the cumulonimbus cloud in a thunderstorm grows vertically, the liquid water droplets freeze when the air temperature reaches the freezing point. The anvil cloud takes its shape because the temperature inversion at the
Type system or an "effect system", which enables even more program specifications to be verified by a type checker. Beyond simple value-type pairs, a virtual "region" of code is associated with an "effect" component describing "what" is being done "with what", and enabling for example to "throw" an error report. Thus the symbolic system may be a "type and effect system", which endows it with more safety checking than type checking alone. Whether automated by the compiler or specified by a programmer, a type system makes program behavior illegal if outside the type-system rules. Advantages provided by programmer-specified type systems include: Advantages