def F(self, getter):<EOL>
return self._compose_optic(optics.Getter(getter))<EOL>
An optic that wraps a getter function. A getter function is
        one that takes a state and returns a value derived from that
        state. The function is called on the focus before it is returned.

            >>> from lenses import lens
            >>> lens.F(abs)
            UnboundLens(Getter(<built-in function abs>))
            >>> lens.F(abs).get()(-1)
            1
            >>> lens.Each().F(abs).collect()([-1, 2, -3])
            [1, 2, 3]

        This optic cannot be used to set or modify values.