We introduce continuous $R$-valuations on directed-complete posets (dcpos,
for short), as a generalization of continuous valuations in domain theory, by
extending values of continuous valuations from reals to so-called Abelian
d-rags $R$.
Like the valuation monad $\mathbf{V}$ introduced by Jones and Plotkin, we
show that the construction of continuous $R$-valuations extends to a strong
monad $\mathbf{V}^R$ on the category of dcpos and Scott-continuous maps.
Additionally, and as in recent work by the two authors and C. Th\'eron, and by
the second author, B. Lindenhovius, M. Mislove and V. Zamdzhiev, we show that
we can extract a commutative monad $\mathbf{V}^R_m$ out of it, whose elements
we call minimal $R$-valuations.
We also show that continuous $R$-valuations have close connections to
measures when $R$ is taken to be $\mathbf{I}\mathbb{R}^\star_+$, the interval
domain of the extended nonnegative reals: (1) On every coherent topological
space, every non-zero, bounded $\tau$-smooth measure $\mu$ (defined on the
Borel $\sigma$-algebra), canonically determines a continuous
$\mathbf{I}\mathbb{R}^\star_+$-valuation; and (2) such a continuous
$\mathbf{I}\mathbb{R}^\star_+$-valuation is the most precise (in a certain
sense) continuous $\mathbf{I}\mathbb{R}^\star_+$-valuation that approximates
$\mu$, when the support of $\mu$ is a compact Hausdorff subspace of a
second-countable stably compact topological space. This in particular applies
to Lebesgue measure on the unit interval. As a result, the Lebesgue measure can
be identified as a continuous $\mathbf{I}\mathbb{R}^\star_+$-valuation.
Additionally, we show that the latter is minimal.