Adding a billion numbers in Rust

It compares the time to Python, based on reduce(lambda...). The lambda x, y: x+y is slower than operator.add:

  % /usr/bin/time -p python -c 'reduce(lambda x,y: x+y, xrange(1000000000))'
  real       140.16
  user       140.10
  sys          0.05
  % /usr/bin/time -p python -c 'import operator; reduce(operator.add, xrange(1000000000))'
  real        67.04
  user        67.02
  sys          0.01

Python is not optimized for functional programming. The idiomatically relevant comparison would be:

  % /usr/bin/time python -c 'sum(xrange(1000000000))'
       11.99 real        11.98 user         0.01 sys
  % /usr/bin/time pypy -c 'sum(xrange(1000000000))'
        1.38 real         1.35 user         0.02 sys

That of course still doesn't beat pre-computation.

But what is the code generated when the value of N is not known at compile time. i.e it is a user provided value (which is the more interesting case since it happens all the time) -- does the fold still get abstracted into a for-loop kind of thing in the generated code?