Parser failed badly; maybe try installing the V8 package

I am a newbie in the field of R and Rstan, and the following stan code is from a literature by kanen et al. (2019). I am trying to replicate their results. However, whenever I check this stan code, it would report a bug like:
“Error in stanc(filename, allow_undefined = TRUE) :
parser failed badly; maybe try installing the V8 package”.
I have sought help from ChatGPT or New Bing, and I installed the package “V8”, updated the R and Rstan, restarted R, as AI suggested. However, this error persisted.
I would really appreciate it if you could help me with this difficulty. The stan code is as follows:

functions {

    // ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    // Common functions
    // ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    // ... substitute in R while there's a bug in rstan's path specification to stan's #include
// #include commonfunc.stan

}

data {
    // ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    // Data
    // ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    // ... substitute in R while there's a bug in rstan's path specification to stan's #include
// #include data.stan
}

transformed data {
    // ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    // Constants
    // ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    // ... substitute in R while there's a bug in rstan's path specification to stan's #include
// #include constants.stan

}

parameters {

    // ========================================================================
    // Fixed effects
    // ========================================================================
    // Some lengthy thought into the best way to code this (e.g. cells means
    // vs effect/dummy coding); see scanned paper document.

    real<lower=0, upper=1> reward_rate_by_group_drug[N_GROUPS, N_DRUGS];
    real<lower=0, upper=1> punish_rate_by_group_drug[N_GROUPS, N_DRUGS];
    real<lower=0> reinf_sensitivity_by_group_drug[N_GROUPS, N_DRUGS];
    real side_stickiness_by_group_drug[N_GROUPS, N_DRUGS];
    real stimulus_stickiness_by_group_drug[N_GROUPS, N_DRUGS];

    // ========================================================================
    // Random effects
    // ========================================================================

    real<lower=0> reward_rate_intersubject_sd;
    real<lower=0> punish_rate_intersubject_sd;
    real<lower=0> reinf_sensitivity_intersubject_sd;
    real<lower=0> side_stickiness_intersubject_sd;
    real<lower=0> stimulus_stickiness_intersubject_sd;

    vector[N_SUBJECTS] reward_rate_subject_effect_raw_unit_normal;
    vector[N_SUBJECTS] punish_rate_subject_effect_raw_unit_normal;
    vector[N_SUBJECTS] reinf_sensitivity_subject_effect_raw_unit_normal;
    vector[N_SUBJECTS] side_stickiness_subject_effect_raw_unit_normal;
    vector[N_SUBJECTS] stimulus_stickiness_subject_effect_raw_unit_normal;
}

transformed parameters {

    vector[N_SUBJECTS] reward_rate_subject_effect;
    vector[N_SUBJECTS] punish_rate_subject_effect;
    vector[N_SUBJECTS] reinf_sensitivity_subject_effect;
    vector[N_SUBJECTS] side_stickiness_subject_effect;
    vector[N_SUBJECTS] stimulus_stickiness_subject_effect;

    reward_rate_subject_effect = getReparameterizedNormal_VRR_lp(
        reward_rate_subject_effect_raw_unit_normal,
        0, reward_rate_intersubject_sd);
    punish_rate_subject_effect = getReparameterizedNormal_VRR_lp(
        punish_rate_subject_effect_raw_unit_normal,
        0, punish_rate_intersubject_sd);
    reinf_sensitivity_subject_effect = getReparameterizedNormal_VRR_lp(
        reinf_sensitivity_subject_effect_raw_unit_normal,
        0, reinf_sensitivity_intersubject_sd);
    side_stickiness_subject_effect = getReparameterizedNormal_VRR_lp(
        side_stickiness_subject_effect_raw_unit_normal,
        0, side_stickiness_intersubject_sd);
    stimulus_stickiness_subject_effect = getReparameterizedNormal_VRR_lp(
        stimulus_stickiness_subject_effect_raw_unit_normal,
        0, stimulus_stickiness_intersubject_sd);
}

model {

    // Calculated probability of choosing the right-hand-side (RHS) stimulus:
    vector[N_TRIALS] p_choose_rhs;

    // ========================================================================
    // Specify priors
    // ========================================================================

    sampleBeta_2RR_lp(reward_rate_by_group_drug, PRIOR_BETA_SHAPE1, PRIOR_BETA_SHAPE2);
    sampleBeta_2RR_lp(punish_rate_by_group_drug, PRIOR_BETA_SHAPE1, PRIOR_BETA_SHAPE2);
    sampleGamma_2RR_lp(reinf_sensitivity_by_group_drug, PRIOR_GAMMA_ALPHA_FOR_REINF_SENSITIVITY_MEAN, PRIOR_GAMMA_BETA_FOR_REINF_SENSITIVITY_MEAN);  // positive only
    sampleNormal_2RR_lp(side_stickiness_by_group_drug, 0, 1);  // can be negative; see Christakou (2013)
    sampleNormal_2RR_lp(stimulus_stickiness_by_group_drug, 0, 1);

    sampleNormalLowerBound_RRR_lp(reward_rate_intersubject_sd, 0, PRIOR_HALF_NORMAL_SD_FOR_SD_IN_RANGE_0_1, 0);  // lower bound of 0
    sampleNormalLowerBound_RRR_lp(punish_rate_intersubject_sd, 0, PRIOR_HALF_NORMAL_SD_FOR_SD_IN_RANGE_0_1, 0);  // lower bound of 0
    sampleNormalLowerBound_RRR_lp(reinf_sensitivity_intersubject_sd, 0, PRIOR_HALF_NORMAL_SIGMA_FOR_REINF_SENSITIVITY_SD, 0);  // lower bound of 0
    sampleNormalLowerBound_RRR_lp(side_stickiness_intersubject_sd, 0, PRIOR_HALF_NORMAL_SD_FOR_SD_IN_RANGE_0_1, 0);  // lower bound of 0
    sampleNormalLowerBound_RRR_lp(stimulus_stickiness_intersubject_sd, 0, PRIOR_HALF_NORMAL_SD_FOR_SD_IN_RANGE_0_1, 0);  // lower bound of 0

    // ========================================================================
    // Reinforcement learning model: calculates p_choose_rhs
    // ========================================================================
    {
        // Start a new block because we will define local-only variables.
        // NO RANGE CONSTRAINTS allowed here.

        // Keeping track of the current subject/drug
        int s = 0; // current subject, starting with an invalid value
        int d; // current drug

        // Value tracking
        vector[N_STIMULI] stim_value;  // value of each stimulus; range -1 to +1

        // Temporary variables: RL calculations
        vector[N_SIDES] values_left_right;
        vector[N_SIDES] side_stickiness_left_right;  // integer contents, but needs to be real for vector multiplication
        vector[N_SIDES] stimulus_stickiness_left_right;  // integer contents, but needs to be real for vector multiplication
        vector[N_SIDES] softmax_inputs;
        int first_trial_of_drug;  // stickiness only makes sense for trialnum > 1
        int chosen_stimulus_index;  // takes values 1 ... N_STIMULI
        real predicted_outcome;
        real actual_outcome;
        real prediction_error;
        real value_change;

        // Temporary variables: final parameter values
        // NO RANGE CONSTRAINTS PERMITTED HERE.
        real reward_rate_final;
        real punish_rate_final;
        real reinf_sensitivity_final;
        real side_stickiness_final;
        real stimulus_stickiness_final;
        real temp_new_value;

        // Iterate through trials
        for (t in 1:N_TRIALS) {
            // Starting a new subject? Read subject parameters and reset discrimination.
            if (s != subject[t]) {
                s = subject[t];
                d = 0; // invalid value; will trigger the "new drug" code below
            }

            // Starting a new drug? Reset starting values.
            if (d != drug[t]) {
                int g = group_membership[s];
                d = drug[t];
                first_trial_of_drug = 1;

                for (stim in 1:N_STIMULI) {  // better way to assign to a vector??
                    stim_value[stim] = 0;  // all stimuli start with neutral value
                }

                reward_rate_final = reward_rate_by_group_drug[g, d] + reward_rate_subject_effect[s];
                punish_rate_final = punish_rate_by_group_drug[g, d] + punish_rate_subject_effect[s];
                reinf_sensitivity_final = reinf_sensitivity_by_group_drug[g, d] + reinf_sensitivity_subject_effect[s];
                side_stickiness_final = side_stickiness_by_group_drug[g, d] + side_stickiness_subject_effect[s];
                stimulus_stickiness_final = stimulus_stickiness_by_group_drug[g, d] + stimulus_stickiness_subject_effect[s];

                reward_rate_final = bound(reward_rate_final, 0, 1);
                punish_rate_final = bound(punish_rate_final, 0, 1);
                reinf_sensitivity_final = boundLower(reinf_sensitivity_final, 0);
                // side_stickiness_final may be negative
                // stimulus_stickiness_final may be negative

            } else {
                first_trial_of_drug = 0;
            }

            // Value:
            values_left_right[LEFT] = stim_value[left_stimulus[t]];
            values_left_right[RIGHT] = stim_value[right_stimulus[t]];

            // Side stickiness:
            if (!first_trial_of_drug) {
                // Assign 1 to the side the subject responded to on the last
                // trial, and 0 to the other side.
                side_stickiness_left_right[RIGHT] = responded_right[t - 1];
                side_stickiness_left_right[LEFT] = 1 - responded_right[t - 1];
            } else {
                // no better way of assigning constant to vector?
                side_stickiness_left_right[RIGHT] = 0;
                side_stickiness_left_right[LEFT] = 0;
            }

            // Stimulus stickiness:
            if (!first_trial_of_drug) {
                // If the stimulus on the right is the same stimulus that the
                // subject responded to on the last trial, "right" gets the
                // value 1. Otherwise 0. And similarly for left.
                int stimulus_chosen_last_trial =
                    responded_right[t - 1]
                    ? right_stimulus[t - 1]
                    : left_stimulus[t - 1];
                stimulus_stickiness_left_right[RIGHT] = right_stimulus[t] == stimulus_chosen_last_trial ? 1 : 0;
                stimulus_stickiness_left_right[LEFT] = left_stimulus[t] == stimulus_chosen_last_trial ? 1 : 0;
            } else {
                stimulus_stickiness_left_right[RIGHT] = 0;
                stimulus_stickiness_left_right[LEFT] = 0;
            }

            // ----------------------------------------------------------------
            // Calculate p
            // ----------------------------------------------------------------

            softmax_inputs = (
                reinf_sensitivity_final * values_left_right +
                side_stickiness_final * side_stickiness_left_right +
                stimulus_stickiness_final * stimulus_stickiness_left_right
            );

            p_choose_rhs[t] = softmaxNth(softmax_inputs, RIGHT);

            // ----------------------------------------------------------------
            // Update
            // ----------------------------------------------------------------

            // We update the value of the thing we chose based on the outcome
            // we received.

            if (responded_right[t]) {
                chosen_stimulus_index = right_stimulus[t];
            } else {
                chosen_stimulus_index = left_stimulus[t];
            }

            predicted_outcome = stim_value[chosen_stimulus_index];
            actual_outcome = outcome[t];
            prediction_error = actual_outcome - predicted_outcome;
            // Since stimulus value starts in the range 0 to +1, and the
            // actual outcome is also in the range 0 to +1, the prediction
            // error has the range 0 to +1.

            if (prediction_error > 0) {
                // better than expected: reward, or extinction of punishment
                value_change = prediction_error * reward_rate_final;
            } else {
                // worse than expected: punishment, or extinction of reward
                // (or prediction_error == 0, in which case it
                // doesn't matter which rate constant we're using!)
                value_change = prediction_error * punish_rate_final;
            }
            // The actual update:
            temp_new_value = predicted_outcome + value_change;
            //               ^^^^^^^^^^^^^^^^^
            // ... NB this is stim_value[chosen_stimulus_index], but it saves
            //     an extra array lookup step.
            if (temp_new_value < 0.0 || temp_new_value > 1.0) {
                reject("Error: stimulus value out of range [0, 1]!");
            }
            stim_value[chosen_stimulus_index] = temp_new_value;

            // Expressed in two equivalent ways, for a single rate example,
            // with v for value:
            // (1)      prediction_error[t] = reinforcement[t] - v[t]
            //          v[t+1] = v[t] + rate * prediction_error[t]
            //
            // (2)      v[t+1] = rate * reinforcement[t] + (1 - rate) * v[t]
            //          ... capturing the "spontaneous decay" element
            //
            // Equivalence:
            // from (1):    v[t+1] = v[t] + rate * (reinforcement[t] - v[t])
            //                     = v[t] + rate * reinforcement[t] - rate * v[t]
            //                     = rate * reinforcement[t] + (1 - rate) * v[t]
        }

    }

    // ========================================================================
    // Final fit to behaviour
    // ========================================================================

    sampleBernoulli_AV_lp(responded_right, p_choose_rhs);

    // ... actual choices predicted from our model-calculated probabilities
    // ... Stan will try to match the model to the behaviour via this.

}

generated quantities {

    // ========================================================================
    // Other stuff we're interested in measuring
    // ========================================================================
    // gmd = group mean difference; ct = contrast

    // ------------------------------------------------------------------------
    // Specific interactions/contrasts of interest
    // ------------------------------------------------------------------------

    // "How do the groups differ intrinsically (on placebo)?"

    real gmd_reward_rate_placebo_ocd_minus_control =
        reward_rate_by_group_drug[OCD_GROUP, PLACEBO_DRUG] -
        reward_rate_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_reward_rate_placebo_stimulant_minus_control =
        reward_rate_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        reward_rate_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_reward_rate_placebo_stimulant_minus_ocd =
        reward_rate_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        reward_rate_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real gmd_punish_rate_placebo_ocd_minus_control =
        punish_rate_by_group_drug[OCD_GROUP, PLACEBO_DRUG] -
        punish_rate_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_punish_rate_placebo_stimulant_minus_control =
        punish_rate_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        punish_rate_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_punish_rate_placebo_stimulant_minus_ocd =
        punish_rate_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        punish_rate_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real gmd_reinf_sensitivity_placebo_ocd_minus_control =
        reinf_sensitivity_by_group_drug[OCD_GROUP, PLACEBO_DRUG] -
        reinf_sensitivity_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_reinf_sensitivity_placebo_stimulant_minus_control =
        reinf_sensitivity_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        reinf_sensitivity_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_reinf_sensitivity_placebo_stimulant_minus_ocd =
        reinf_sensitivity_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        reinf_sensitivity_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real gmd_side_stickiness_placebo_ocd_minus_control =
        side_stickiness_by_group_drug[OCD_GROUP, PLACEBO_DRUG] -
        side_stickiness_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_side_stickiness_placebo_stimulant_minus_control =
        side_stickiness_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        side_stickiness_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_side_stickiness_placebo_stimulant_minus_ocd =
        side_stickiness_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        side_stickiness_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real gmd_stimulus_stickiness_placebo_ocd_minus_control =
        stimulus_stickiness_by_group_drug[OCD_GROUP, PLACEBO_DRUG] -
        stimulus_stickiness_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_stimulus_stickiness_placebo_stimulant_minus_control =
        stimulus_stickiness_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        stimulus_stickiness_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real gmd_stimulus_stickiness_placebo_stimulant_minus_ocd =
        stimulus_stickiness_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG] -
        stimulus_stickiness_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    // "What do the drugs do in the control group?"

    real ct_reward_rate_amisulpride_effect_in_control_group =
        reward_rate_by_group_drug[CONTROL_GROUP, AMISULPRIDE_DRUG] -
        reward_rate_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_reward_rate_pramipexole_effect_in_control_group =
        reward_rate_by_group_drug[CONTROL_GROUP, PRAMIPEXOLE_DRUG] -
        reward_rate_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_punish_rate_amisulpride_effect_in_control_group =
        punish_rate_by_group_drug[CONTROL_GROUP, AMISULPRIDE_DRUG] -
        punish_rate_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_punish_rate_pramipexole_effect_in_control_group =
        punish_rate_by_group_drug[CONTROL_GROUP, PRAMIPEXOLE_DRUG] -
        punish_rate_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_reinf_sensitivity_amisulpride_effect_in_control_group =
        reinf_sensitivity_by_group_drug[CONTROL_GROUP, AMISULPRIDE_DRUG] -
        reinf_sensitivity_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_reinf_sensitivity_pramipexole_effect_in_control_group =
        reinf_sensitivity_by_group_drug[CONTROL_GROUP, PRAMIPEXOLE_DRUG] -
        reinf_sensitivity_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_side_stickiness_amisulpride_effect_in_control_group =
        side_stickiness_by_group_drug[CONTROL_GROUP, AMISULPRIDE_DRUG] -
        side_stickiness_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_side_stickiness_pramipexole_effect_in_control_group =
        side_stickiness_by_group_drug[CONTROL_GROUP, PRAMIPEXOLE_DRUG] -
        side_stickiness_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_stimulus_stickiness_amisulpride_effect_in_control_group =
        stimulus_stickiness_by_group_drug[CONTROL_GROUP, AMISULPRIDE_DRUG] -
        stimulus_stickiness_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    real ct_stimulus_stickiness_pramipexole_effect_in_control_group =
        stimulus_stickiness_by_group_drug[CONTROL_GROUP, PRAMIPEXOLE_DRUG] -
        stimulus_stickiness_by_group_drug[CONTROL_GROUP, PLACEBO_DRUG];

    // "... in the stimulant abuse group?"

    real ct_reward_rate_amisulpride_effect_in_stimulant_group =
        reward_rate_by_group_drug[STIMULANT_GROUP, AMISULPRIDE_DRUG] -
        reward_rate_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_reward_rate_pramipexole_effect_in_stimulant_group =
        reward_rate_by_group_drug[STIMULANT_GROUP, PRAMIPEXOLE_DRUG] -
        reward_rate_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_punish_rate_amisulpride_effect_in_stimulant_group =
        punish_rate_by_group_drug[STIMULANT_GROUP, AMISULPRIDE_DRUG] -
        punish_rate_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_punish_rate_pramipexole_effect_in_stimulant_group =
        punish_rate_by_group_drug[STIMULANT_GROUP, PRAMIPEXOLE_DRUG] -
        punish_rate_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_reinf_sensitivity_amisulpride_effect_in_stimulant_group =
        reinf_sensitivity_by_group_drug[STIMULANT_GROUP, AMISULPRIDE_DRUG] -
        reinf_sensitivity_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_reinf_sensitivity_pramipexole_effect_in_stimulant_group =
        reinf_sensitivity_by_group_drug[STIMULANT_GROUP, PRAMIPEXOLE_DRUG] -
        reinf_sensitivity_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_side_stickiness_amisulpride_effect_in_stimulant_group =
        side_stickiness_by_group_drug[STIMULANT_GROUP, AMISULPRIDE_DRUG] -
        side_stickiness_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_side_stickiness_pramipexole_effect_in_stimulant_group =
        side_stickiness_by_group_drug[STIMULANT_GROUP, PRAMIPEXOLE_DRUG] -
        side_stickiness_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_stimulus_stickiness_amisulpride_effect_in_stimulant_group =
        stimulus_stickiness_by_group_drug[STIMULANT_GROUP, AMISULPRIDE_DRUG] -
        stimulus_stickiness_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    real ct_stimulus_stickiness_pramipexole_effect_in_stimulant_group =
        stimulus_stickiness_by_group_drug[STIMULANT_GROUP, PRAMIPEXOLE_DRUG] -
        stimulus_stickiness_by_group_drug[STIMULANT_GROUP, PLACEBO_DRUG];

    // "... in the OCD group?"

    real ct_reward_rate_amisulpride_effect_in_ocd_group =
        reward_rate_by_group_drug[OCD_GROUP, AMISULPRIDE_DRUG] -
        reward_rate_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_reward_rate_pramipexole_effect_in_ocd_group =
        reward_rate_by_group_drug[OCD_GROUP, PRAMIPEXOLE_DRUG] -
        reward_rate_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_punish_rate_amisulpride_effect_in_ocd_group =
        punish_rate_by_group_drug[OCD_GROUP, AMISULPRIDE_DRUG] -
        punish_rate_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_punish_rate_pramipexole_effect_in_ocd_group =
        punish_rate_by_group_drug[OCD_GROUP, PRAMIPEXOLE_DRUG] -
        punish_rate_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_reinf_sensitivity_amisulpride_effect_in_ocd_group =
        reinf_sensitivity_by_group_drug[OCD_GROUP, AMISULPRIDE_DRUG] -
        reinf_sensitivity_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_reinf_sensitivity_pramipexole_effect_in_ocd_group =
        reinf_sensitivity_by_group_drug[OCD_GROUP, PRAMIPEXOLE_DRUG] -
        reinf_sensitivity_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_side_stickiness_amisulpride_effect_in_ocd_group =
        side_stickiness_by_group_drug[OCD_GROUP, AMISULPRIDE_DRUG] -
        side_stickiness_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_side_stickiness_pramipexole_effect_in_ocd_group =
        side_stickiness_by_group_drug[OCD_GROUP, PRAMIPEXOLE_DRUG] -
        side_stickiness_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_stimulus_stickiness_amisulpride_effect_in_ocd_group =
        stimulus_stickiness_by_group_drug[OCD_GROUP, AMISULPRIDE_DRUG] -
        stimulus_stickiness_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    real ct_stimulus_stickiness_pramipexole_effect_in_ocd_group =
        stimulus_stickiness_by_group_drug[OCD_GROUP, PRAMIPEXOLE_DRUG] -
        stimulus_stickiness_by_group_drug[OCD_GROUP, PLACEBO_DRUG];

    // "Is the effect of amisulpride different in stimulant abusers to controls?"

    real ct_reward_rate_amisulpride_effect_for_stimulant_minus_control = (
        ct_reward_rate_amisulpride_effect_in_stimulant_group -
        ct_reward_rate_amisulpride_effect_in_control_group
    );
    real ct_punish_rate_amisulpride_effect_for_stimulant_minus_control = (
        ct_punish_rate_amisulpride_effect_in_stimulant_group -
        ct_punish_rate_amisulpride_effect_in_control_group
    );
    real ct_reinf_sensitivity_amisulpride_effect_for_stimulant_minus_control = (
        ct_reinf_sensitivity_amisulpride_effect_in_stimulant_group -
        ct_reinf_sensitivity_amisulpride_effect_in_control_group
    );
    real ct_side_stickiness_amisulpride_effect_for_stimulant_minus_control = (
        ct_side_stickiness_amisulpride_effect_in_stimulant_group -
        ct_side_stickiness_amisulpride_effect_in_control_group
    );
    real ct_stimulus_stickiness_amisulpride_effect_for_stimulant_minus_control = (
        ct_stimulus_stickiness_amisulpride_effect_in_stimulant_group -
        ct_stimulus_stickiness_amisulpride_effect_in_control_group
    );

    // "... and of pramipexole?"

    real ct_reward_rate_pramipexole_effect_for_stimulant_minus_control = (
        ct_reward_rate_pramipexole_effect_in_stimulant_group -
        ct_reward_rate_pramipexole_effect_in_control_group
    );
    real ct_punish_rate_pramipexole_effect_for_stimulant_minus_control = (
        ct_punish_rate_pramipexole_effect_in_stimulant_group -
        ct_punish_rate_pramipexole_effect_in_control_group
    );
    real ct_reinf_sensitivity_pramipexole_effect_for_stimulant_minus_control = (
        ct_reinf_sensitivity_pramipexole_effect_in_stimulant_group -
        ct_reinf_sensitivity_pramipexole_effect_in_control_group
    );
    real ct_side_stickiness_pramipexole_effect_for_stimulant_minus_control = (
        ct_side_stickiness_pramipexole_effect_in_stimulant_group -
        ct_side_stickiness_pramipexole_effect_in_control_group
    );
    real ct_stimulus_stickiness_pramipexole_effect_for_stimulant_minus_control = (
        ct_stimulus_stickiness_pramipexole_effect_in_stimulant_group -
        ct_stimulus_stickiness_pramipexole_effect_in_control_group
    );

    // "Is the effect of amisulpride different in OCD to controls?"

    real ct_reward_rate_amisulpride_effect_for_ocd_minus_control = (
        ct_reward_rate_amisulpride_effect_in_ocd_group -
        ct_reward_rate_amisulpride_effect_in_control_group
    );
    real ct_punish_rate_amisulpride_effect_for_ocd_minus_control = (
        ct_punish_rate_amisulpride_effect_in_ocd_group -
        ct_punish_rate_amisulpride_effect_in_control_group
    );
    real ct_reinf_sensitivity_amisulpride_effect_for_ocd_minus_control = (
        ct_reinf_sensitivity_amisulpride_effect_in_ocd_group -
        ct_reinf_sensitivity_amisulpride_effect_in_control_group
    );
    real ct_side_stickiness_amisulpride_effect_for_ocd_minus_control = (
        ct_side_stickiness_amisulpride_effect_in_ocd_group -
        ct_side_stickiness_amisulpride_effect_in_control_group
    );
    real ct_stimulus_stickiness_amisulpride_effect_for_ocd_minus_control = (
        ct_stimulus_stickiness_amisulpride_effect_in_ocd_group -
        ct_stimulus_stickiness_amisulpride_effect_in_control_group
    );

    // "... and of pramipexole?"

    real ct_reward_rate_pramipexole_effect_for_ocd_minus_control = (
        ct_reward_rate_pramipexole_effect_in_ocd_group -
        ct_reward_rate_pramipexole_effect_in_control_group
    );
    real ct_punish_rate_pramipexole_effect_for_ocd_minus_control = (
        ct_punish_rate_pramipexole_effect_in_ocd_group -
        ct_punish_rate_pramipexole_effect_in_control_group
    );
    real ct_reinf_sensitivity_pramipexole_effect_for_ocd_minus_control = (
        ct_reinf_sensitivity_pramipexole_effect_in_ocd_group -
        ct_reinf_sensitivity_pramipexole_effect_in_control_group
    );
    real ct_side_stickiness_pramipexole_effect_for_ocd_minus_control = (
        ct_side_stickiness_pramipexole_effect_in_ocd_group -
        ct_side_stickiness_pramipexole_effect_in_control_group
    );
    real ct_stimulus_stickiness_pramipexole_effect_for_ocd_minus_control = (
        ct_stimulus_stickiness_pramipexole_effect_in_ocd_group -
        ct_stimulus_stickiness_pramipexole_effect_in_control_group
    );

}

Edited by @jsocolar for syntax highlighting

Before diving into the Kanen et al. (2019) model code, can you confirm that you’re able to compile and sample from a model, by running the rstan example:

example(stan_model, package = "rstan", run.dontrun = TRUE)

I’m not sure the following will solve your problems, but just FYI I noticed a few syntax errors at least in the parameters block. The fixed effects parameters are defined using a deprecated syntax. For newer versions of Stan, a line like this:

real<lower=0, upper=1> reward_rate_by_group_drug[N_GROUPS, N_DRUGS];

needs to be replaced with this:

array[N_GROUPS, N_DRUGS] real<lower=0, upper=1> reward_rate_by_group_drug;

The Stan code as shown is unlikely to be complete, as the entire data block is commented out.

The source of the error that you are seeing is likely due to the existence of the pound character # in a comment (e.g. on the final lines of the functions and data blocks). This does not play nicely with Rstan.

Yes exactly, it looks like the Stan code for the functions, data, and transformed data blocks is defined in separate files that are loaded using the include function, except these lines are currently commented out.

The code in the functions block will need to be added at the very least, as the transformed parameters and model blocks include calls to various user-defined functions.

yes, if you search for the paper online, they have an R script that reads in the code for the include statements and then substitutes it into the stan code: https://static-content.springer.com/esm/art%3A10.1007%2Fs00213-019-05325-w/MediaObjects/213_2019_5325_MOESM2_ESM.r

so @upup hopefully you can use the R script to replicate their results