= Solution
Generate each row of <Pascal's triangle> from its predecessor, padding at opposite ends before adding corresponding entries:
``
pascal :: Num a => [[a]]
pascal = iterate next [1]
where
next :: Num a => [a] -> [a]
next row = zipWith (+) (0:row) (row ++ [0])
``
The boundary sums are the old endpoint plus zero, and the interior sums satisfy <Pascal's rule>. <Induction> on the iteration number therefore gives the rows of <binomial coefficients>. The outer <lazy list> is infinite, with each finite row available on demand. Instantiate `a` as `Integer` for exact arbitrarily large entries; bounded machine integers eventually overflow.
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