A "parser expected:" warning on a code that works

Developers
1

Dear all,

I hope this message finds you well. I have been using Stan for sometime now and its quite fun. I have implemented an ICAR model inspired by Prof. Mitzi Morris’ tutorial [HERE]

functions {
	real icar_normal_lpdf(vector phi, int N, array[] int node1, array[] int node2) {
		return -0.5 * dot_self(phi[node1] - phi[node2]);
	}
}
data {
	int<lower=0> N;
	int<lower=0> N_edges;
	array[N_edges] int<lower=1, upper=N> node1;
	array[N_edges] int<lower=1, upper=N> node2;
	array[N] int<lower=0> Y;
	vector<lower=0>[N] E;
}
transformed data {
	vector[N] log_exposure = log(E);
}
parameters {
	real alpha;
	real<lower=0> sigma;
	vector[N] phi;
}
model {
	phi ~ icar_normal(N, node1, node2);
	Y ~ poisson_log(log_exposure + alpha + phi*sigma);
	alpha ~ normal(0.0, 1.0);
	sigma ~ normal(0.0, 1.0);
	sum(phi) ~ normal(0, 0.001*N);
}
generated quantities {
	vector[N] eta = alpha + phi*sigma;
	vector[N] mu = exp(eta);
}

The above code works perfectly on one of my machines (i.e., Mac-mini). However, I am using the same code on a different computer (i.e., MacBook pro) and I get this confusing “parser expected” warning in the function line.

SYNTAX ERROR, MESSAGE(S) FROM PARSER:
 error in 'model1443186a5e0b_icar_poisson_model' at line 2, column 43
  -------------------------------------------------
     1: functions {
     2: 	real icar_normal_lpdf(vector phi, int N, array[] int node1, array[] int node2) {
                                                  ^
     3: 		return -0.5 * dot_self(phi[node1] - phi[node2]);
  -------------------------------------------------

PARSER EXPECTED: <argument declaration or close paren ) to end argument declarations>
Error in stanc(file = file, model_code = model_code, model_name = model_name,  : 
  failed to parse Stan model 'icar_poisson_model' due to the above error.

I am having difficulties overcoming this issue on my MacBook Pro. Also, I don’t understand why don’t get this ‘parser’ problem on one of my computer, but it appearing in another machine. I am developing a practical session of an MSc module and I can imagine different students writing the same code but this parser warning appearing on different machines.

Any help or solutions will be appreciated. Thank you.

Anwar.

2

This is just a guess, but maybe replace the phi ~ icar_normal line with

target += icar_normal_lpdf(phi | N, node1, node2);

I seem to recall that functions ending in _lpdf have some special usage that is different than other functions. So besides above, you might also try renaming the function and keeping the phi ~ thing.

Also, N is not used in the function, so it seems you could remove that argument.

1 Like
3

@edm, thank you very much for the suggestions.

I have implemented the changes you suggested but I unfortunately I am still greeted with this error. This error message is quite baffling… the same above script runs nicely on my desktop with no problems flagged. But when I open the same script on my laptop this error appears. It’s indeed quite confusing.

Thank you again for the suggestions.

4

The Stan code in your post seems to work for me. What versions are you using on the system which produces this error?

2 Likes
5

Hello @WardBrian, thank you very much - your message alone has provided me the solution! I am now realising something… my desktop was using the latest development version of RStan (i.e., 2.26.13) which the script worked fine; however, my laptop had the 2.21.1 version of RStan which for some reason my script didn’t work on.

I have removed the 2.21.1 version of RStan and installed version 2.26.13 [see here]. The script works perfectly now. Thank you very much - your message has made things click!

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