The easiest way to link to the current directory as an absolute path, without typing the whole path string would be
ln -s "$(pwd)/foo" ~/bin/foo_link
target (first) argument for the
ln -s command works relative to the symbolic link's location, not your current directory. It helps to know that, essentially, the created symlink (the second argument) simply holds the text you provide for the first argument.
Therefore, if you do the following:
ln -s foo foo_link
and then move that link around
mv foo_link ../some_other_directory
ls -l ../some_other_directory
you will see that
foo_link tries to point to
foo in the directory it is residing in. This also works with symbolic links pointing to relative paths. If you do the following:
ln -s ../foo yet_another_link
and then move
yet_another_link to another directory and check where it points to, you'll see that it always points to
../foo. This is the intended behaviour, since many times symbolic links might be part of a directory structure that can reside in various absolute paths.
In your case, when you create the link by typing
ln -s foo ~/bin/foo_link
foo_link just holds a link to
foo, relative to its location. Putting
$(pwd) in front of the target argument's name simply adds the current working directory's absolute path, so that the link is created with an absolute target.