These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.00 s (backtrack: 0/20).

[ebuild  N     ] dev-cpp/yaml-cpp-0.9.0-r1:0/0.9::gentoo  USE="-test" 1032 KiB
[ebuild  N     ] app-laptop/thinkfan-1.3.1::gentoo  USE="yaml -atasmart -nvidia" 86 KiB

Total: 2 packages (2 new), Size of downloads: 1117 KiB