7 Mar
2003
7 Mar
'03
4:40 a.m.
"mike V"
The nhc98 compiler already accepts a `deriving Binary' clause. DrIFT likewise already supports {-! derives : Binary !-}.
What was the strategy employed to derive instances of sum types, i.e. the binary representation?
For a sum-of-products type with n constructors, represent the constructor as a bit sequence of length ceiling(log n), and then simply append the binary representation of each product component. This gives a nice generic scheme, although of course it is possible to write instances manually that yield a higher compression. For instance in some applications we used Huffman encoding based on the frequency of occurrence of each constructor. Regards, Malcolm