Accepts one call to an allowlisted distribution whose arguments are all
finite numeric constants, such as "normal(0, 1)" or
"student_t(3, 0, 2.5)". Statement separators, braces, target
increments, nested calls (reject(), exp()), constant(), and symbols
are rejected. With class, the distribution must suit that parameter
class: location families for b and Intercept; student_t, normal,
exponential, gamma, inv_gamma, cauchy for scale classes (brms adds
the lower bound); lkj for cor; and normal or uniform for ar and
ma, whose location must lie inside [-1, 1] and, for uniform, both
bounds as well.
Details
Each distribution takes its own number of arguments, and scale, degrees
of freedom, shape, rate, and eta arguments must be positive:
normal(mu, sigma), student_t(nu, mu, sigma), cauchy(mu, sigma),
skew_normal(xi, omega, alpha), logistic(mu, sigma),
double_exponential(mu, sigma), exponential(rate), gamma(a, b),
inv_gamma(a, b), lkj(eta), lkj_corr_cholesky(eta), and
uniform(a, b) with a < b. uniform is accepted only with class
"ar" or "ma"; without class or for any other class it is rejected.
Numbers must be
plain decimals (optionally
with an exponent); hexadecimal or L-suffixed literals, comments, and
line breaks are rejected.