Parse pkg string and return a tuple of package name, separator, and
    package version.

    Cabal support install package with following format:

    * foo-1.0
    * foo < 1.2
    * foo > 1.3

    For the sake of simplicity only the first form is supported,
    support for other forms can be added later.

def _parse_pkg_string(pkg):
    '''
    Parse pkg string and return a tuple of package name, separator, and
    package version.

    Cabal support install package with following format:

    * foo-1.0
    * foo < 1.2
    * foo > 1.3

    For the sake of simplicity only the first form is supported,
    support for other forms can be added later.
    '''
    pkg_name, separator, pkg_ver = pkg.partition('-')
    return (pkg_name.strip(), separator, pkg_ver.strip())