Yields the successor of the backwards-binary number in register 1.

 *Language.TRM> decodeBB <$> phi succBB [(1, encodeBB 0)]
 Just 1
 *Language.TRM> decodeBB <$> phi succBB [(1, encodeBB 119)]
 Just 120

Yields the sum of two backwards-binary numbers in registers 1 and 2.

 *Language.TRM> decodeBB <$> phi plusBB [(1, encodeBB 2), (2, encodeBB 3)]
 Just 5
 *Language.TRM> decodeBB <$> phi plusBB [(1, encodeBB 100), (2, encodeBB 20)]
 Just 120

Compares the contents of the given registers for equality, leaving a 1 in the first register if they are, or nothing otherwise. The contents of both registers are destroyed in the process.

Add the two argument registers using primitive recursion, leaving the result in the first.

 *Language.TRM.Programs> decodeBB <$> runL (addBB 1 2) [(1, encodeBB 100), (2, encodeBB 20)]
 Just 120