Constructing Recursive Data Structures

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Functors allow constructing recursive data structures

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Simplest recursive data structure: Peano natural numbers

• z is a Peano number (meaning zero, 0)
• s(N) is a Peano number if N is a Peano number
  (meaning the successor of $N$, i.e., $N + 1$)

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Logic characterization of Peano numbers:

natural(z).
natural(s(N)):- natural(N).

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Note: very similar to the CLP($\Re$) program