  We reanalize data collected with the DarkSide-50 experiment and recently used
to set limits on the spin-independent interaction rate of weakly interacting
massive particles (WIMPs) on argon nuclei with an effective field theory
framework. The dataset corresponds to a total (16660 $\pm$ 270) kg d exposure
using a target of low-radioactivity argon extracted from underground sources.
We obtain upper limits on the effective couplings of the 12 leading operators
in the nonrelativistic systematic expansion. For each effective coupling we set
constraints on WIMP-nucleon cross sections, setting upper limits between $2.4
\times 10^{-45} \, \mathrm{cm}^2$ and $2.3 \times 10^{-42} \, \mathrm{cm}^2$
(8.9 $\times 10^{-45} \, \mathrm{cm}^2$ and 6.0 $\times 10^{-42} \,
\mathrm{cm}^2$) for WIMPs of mass of 100 $\mathrm{GeV/c^2}$ (1000
$\mathrm{GeV/c^2}$) at 90\% confidence level.
