study of the swift development
installation of swift4 to Ubuntu 14.04.5
$ wget https://swift.org/builds/swift-4.0.3-release/ubuntu1404/swift-4.0.3-RELEASE/swift-4.0.3-RELEASE-ubuntu14.04.tar.gz
$ tar zxvf swift-4.0.3-RELEASE-ubuntu14.04.tar.gz
$ mv swift-4.0.3-RELEASE-ubuntu14.04 swift
$ mv swift ~/
$ 'export PATH=~/swift/usr/bin:$PATH' >>~/.profile
$ source ~/.profile
$ swift -v