  Leptonic and semileptonic meson decays that proceed via flavour-changing
neutral currents provide excellent probes of physics of the standard model and
beyond. We present explicit results for the Wilson coefficients of the weak
effective Lagrangian for these decays in any perturbative model in which these
processes proceed via one-loop contributions. We explicitly show that our
results are finite and gauge independent, and provide Mathematica code that
implements our results in an easily usable form.
