Compilation error fitting the Stan model

I encountered compilation errors when fitting a Stan model as below,

fit1 <- stan(file='mystancode.stan', data=ds, refresh=1000, warmup = 2000, iter = 4000, cores = 1, chains=4, seed=100)

Within mystancode.stan, I defined an improper prior distribution on param as below,

functions { // declare and define user-defined function before calling it
real gen_penalty_lpdf(vector param, real s1, real s2, real s3) {
return -s1 * fabs(param[1])-s2 * fabs(param[2])-s3 * fabs(param[1]*param[2]);
}
}

And the error messages are,

trying deprecated constructor; please alert package maintainer
Error in new_CppObject_xp(fields$.module, fields$.pointer, ...) :
no valid constructor available for the argument list
failed to create the sampler; sampling not done

Any help or advice would be greatly appreciated!!!

RStan Version:

The version of RStan you are running (e.g., from packageVersion("rstan"))
‘2.17.2’

R Version:

The version of R you are running (e.g., from R.version.string)
3.5.1

Start by reproducing the stan call from the issue with RStan 2.17.2, R 3.5.1, and the supplied mystancode.stan function. Inspect whether the compilation failure comes from the model definition or the deprecated-constructor error, then document a reproducible cause and confirmed resolution.