Does GHC do dead code elimination? I observe that if you take a module and edit it so that some function is now no longer exported or called by any exported function, the size of the *.o file seems to go down. This suggests that dead code within a single module is eliminated. However... how about this? module Foo where f = ... g = ... h = ... module Main where import Foo main = ...f... Will the generated executable contain the code for g and h, even though they aren't called? Or does the unused code get eliminated? How about the standard libraries? I read somewhere that if one funtion returns a tuple, and the caller immediately extracts the values from the tuple, GHC tries to optimise away the tuple - so it's as if the function can just return multiple values at once. Is this true? Does it apply only to tuples, or to all types?