Tabulation has an instance of AltTable, which is intended to uphold the following law:
fromQuery a <|>: fromQuery b = fromQuery (a <|>: b)
The previous implementation was not actually defined in terms of Query's <|>: (i.e., UNION ALL), because not every Tabulation can be safely toQuery'd. Instead it used a combination of alignWith, catNonEmptyTable and some that worked even on "magic" Tabulations.
However, using unsafePeekQuery, we can actually "statically" determine if a Tabulation is "magic" or not, which means we can selectively switch the implementation to use Query's <|>: where possible. This produces a simpler and usually faster query.
Tabulationhas an instance ofAltTable, which is intended to uphold the following law:The previous implementation was not actually defined in terms of
Query's<|>:(i.e.,UNION ALL), because not everyTabulationcan be safelytoQuery'd. Instead it used a combination ofalignWith,catNonEmptyTableandsomethat worked even on "magic"Tabulations.However, using
unsafePeekQuery, we can actually "statically" determine if aTabulationis "magic" or not, which means we can selectively switch the implementation to useQuery's<|>:where possible. This produces a simpler and usually faster query.