Some custom functions which is not present yet in containers, but needed for me.

Functions to get a part of sequence in a IntMap a.

A function to get a part of sequence in a IntMap a by its key which are bigger or equal than lower bound and smaller or equal than upper bound. It is equivalent to filterWithKey (\k _ -> lowerBound <= k && k <= upperBound).

A function to get a part of sequence in a IntMap a by its key which covers lower bound and upper bound. It is equivalent to limitedOf lowerBound upperBound t + lookupLT lowerBound t + lookupGT upperBound t.

Maybe internal function. Bounding/Limiting at masking level. This post process should be finished very quickly, and not duplicate with boundedOf/limitedOf.

Not yet.... I nearly understand that how IntMap is constructed and how prefix and mask work, but I'm not sure that I understand it perfectly....

Tested by QuickCheck. This may not cover all of boundary conditions. Tested cases are recorded in testset.hs.