Exponentiation needs PrelRules

When a user writes a ^ lb, where lb is an integer literal, the type of lb defaults to Integer unless it's annotated. If lb is very small, then RULES will expand the whole expression into a few multiplications. If not, the computation will pay the price of Integer arithmetic. If we want, we should be able to improve this with a special compilation rule. When lb :: Integer, and 0 <= lb <= maxBound :: Word, we should be able to replace lb by the equivalent Word. The same problem appears with ^^ and stimes. Perhaps those can be fixed up as well, somehow.

Trac metadata

Trac field	Value
Version	8.6.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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