Indicates that it may be beneficial to evaluate the first argument in
parallel with the second. Returns the value of the second argument.
a `par` b is exactly equivalent semantically to
b.
par is generally used when the value of
a is likely
to be required later, but not immediately. Also it is a good idea to
ensure that
a is not a trivial computation, otherwise the
cost of spawning it in parallel overshadows the benefits obtained by
running it in parallel.
Note that actual parallelism is only supported by certain
implementations (GHC with the
-threaded option, and GPH, for
now). On other implementations,
par a b = b.