On 10/8/12 7:27 AM, Simon Marlow wrote:
Code size? It might only be a small effect for most code, but we occasionally see large files of automatically-generated data declarations.
Also I rather like it that making a new data type is so cheap in terms of code size. A single module containing "data T = A | B":
$ size foo.o text data bss dec hex filename 91 32 0 123 7b foo.o
If I add "deriving Typeable":
text data bss dec hex filename 587 312 0 899 383 foo.o
7x larger!
Just in terms of optimization: because they're so lightweight, I've been a big fan of making new data types whenever the slightest need arises--- as opposed to the common practice in other languages of using some "close enough" data type to avoid making a new one. For example, with accumulator-based functions I often codify the accumulator with a data type to help clarify the code and ensure the appropriate strictness. The majority of these throw-away data types are ones which are only used internally and will never leave the module. It'd be nice, therefore, to only autogenerate Typeable instances for data types which actually have a chance of needing them--- i.e., are exported (or use Typeable internally). -- Live well, ~wren