11/12/2009
Attended: Ian, Ivan, Jason, Maya, Mikael, Steve, Vlad
Topics discussed:
- since not everyone has (read) the first 50 pages yet, we'll return to reviewing the book exercises at our next meeting
- Mikael explained Lambek lemma (an initial algebra over an endofunctor is always an isomorphism - so it is also a fixed point)
- discussed examples of such algebras: 1+A (a kind of Maybe monad) gives us NNO as the initial algebra; 1+AX gives an object of all lists: List[A] = A*
- discussed formal derivatives of ADT functors that are used in zippers
- discussed the way to implement unordered pair; can it be called AxA/2?; can we have exp(A) = 1 + A + AxA/2 + ...? Actually, it is not a power set (power bag rather)
(if I missed/misrepresented something, please update)
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