Karczmarczuk’s solution via the Haskell prelude:
part = 1 : b 1 where b n = (1 : b (n + 1)) + (replicate n 0 ++ b n)
This is broken code, no?, just 2 reasons I can spot why: - function 'b n' calls 'b n' unconditionally (infite loop) - What is the reutrn type of 'b'? It seems like it returns list, but the return value is in the form 'a + b' , where (+) is instance of num so I don't think prelude contains any ad-hoc definition of (+) that returns list
Not broken, just insufficiently documented. "part "is supposed to produce an infinite stream whose nth element is the number of distinct representations of n as a sum of positive integers. The "infinite loop" is deliberate, quite like ones = 1 : ones which generates an infinite sequence of 1s. It is not stated, but the (+) is understood to have been overloaded to handle lists of Nums in the natural way Doug