Hi Cristian,
On Dec 30, 2007 6:10 PM, Cristian Baboi
What I don't get it :
(s a1 a2 ... at) must be the value of A in the semantic domain. Let call that value a. Then how can one know if a was built with (s a1 a2 ... at) and not with (egg b1 b2) ?
Because the semantic domain is chosen so that (s a1 a2 ... at) and (egg b1 b2) are distinct objects. More precisely, the domain corresponding to (for example) the type data T = C1 T11 T12 | C2 T21 T22 should be isomorphic to the domain [[T]] = lift (([[T11]] * [[T12]]) + ([[T21]] * [[T22]])) where * is cartesian product, + is disjoint sum (e.g., X+Y = {(1,x) | x in X} union {(2,y) | y in Y}, and 'lift' adds the bottom element to the domain. So here, C1 and C2 correspond to the two sides of the disjoint sum, meaning you can tell them apart. Hope that helps? - Benja