Nimbostratus cloud to a surface observer. Nimbostratus usually has a thickness of about 2000 to 4000 m. Though found worldwide, nimbostratus occurs more commonly in the middle latitudes. It is coded C2 on the SYNOP report. Nimbostratus occurs along a warm front or occluded front where the slowly rising warm air mass creates nimbostratus along with shallower stratus clouds producing less rain, these clouds being preceded by higher-level clouds such as cirrostratus and altostratus. Often, when an altostratus cloud thickens and descends into lower altitudes, it will become nimbostratus. Nimbostratus, unlike cumulonimbus, is not associated with thunderstorms, however at an unusually unstable
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