Brent Yorgey wrote:
Daryoush Mehrtash wrote:
What is (or where do you see) the computational overhead of the "data" declrations?
So, to answer your question, the only computational overhead with a data declaration is the extra memory and time to store and process the constructor tags. It usually isn't noticeable, but sometimes the difference can be important.
Another important part of this that wasn't mentioned is pattern matching. For datatypes with only one constructor there's only one branch to choose among for (one-ply deep) patterns, and so the matching can be skipped entirely. This saves a conditional/vector jump, which can dramatically affect cache behavior. Not needing to pattern match also allows unpacking of the arguments to the constructor into arguments to the function, thus saving on allocation and garbage collection. More importantly, if the arguments are primitive types and strict then they can be unboxed into registers as well. In principle many of these optimizations can be and are applied to single-constructor 'data' types, but using 'newtype' tells the compiler to be sure to optimize them thusly. -- Live well, ~wren