diff --git a/src/builtins/numbers.rs b/src/builtins/numbers.rs
index 7b48eae6..ad199de0 100644
--- a/src/builtins/numbers.rs
+++ b/src/builtins/numbers.rs
@@ -78,8 +78,7 @@ fn range(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     }
     let incr = if v2 >= v1 { 1 } else { -1 } as Float;
 
-    let mut values = vec![];
-    values.reserve((v2 - v1).abs() as usize + 1);
+    let mut values = Vec::with_capacity((v2 - v1).abs() as usize + 1);
 
     let mut v = v1;
     while v != v2 {
diff --git a/src/engine.rs b/src/engine.rs
index 623d8aca..ef8b9b8e 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -6,6 +6,7 @@ use crate::interpreter::*;
 use crate::lexer::*;
 use crate::parser::*;
 use crate::scheduler::*;
+use crate::utils::gather_functions;
 use crate::value::*;
 
 use anyhow::Result;
@@ -13,8 +14,8 @@ use anyhow::Result;
 #[derive(Clone)]
 pub struct Engine {
     modules: Vec<Ref<Module>>,
-    input: Value,
-    data: Value,
+    interpreter: Interpreter,
+    prepared: bool,
 }
 
 impl Default for Engine {
@@ -27,8 +28,8 @@ impl Engine {
     pub fn new() -> Self {
         Self {
             modules: vec![],
-            input: Value::new_object(),
-            data: Value::new_object(),
+            interpreter: Interpreter::new(),
+            prepared: false,
         }
     }
 
@@ -36,6 +37,8 @@ impl Engine {
         let source = Source::new(path, rego);
         let mut parser = Parser::new(&source)?;
         self.modules.push(Ref::new(parser.parse()?));
+        // if policies change, interpreter needs to be prepared again
+        self.prepared = false;
         Ok(())
     }
 
@@ -43,36 +46,105 @@ impl Engine {
         let source = Source::from_file(path)?;
         let mut parser = Parser::new(&source)?;
         self.modules.push(Ref::new(parser.parse()?));
+        self.prepared = false;
         Ok(())
     }
 
     pub fn set_input(&mut self, input: Value) {
-        self.input = input;
+        self.interpreter.set_input(input);
     }
 
     pub fn clear_data(&mut self) {
-        self.data = Value::new_object();
+        self.interpreter.set_data(Value::new_object());
+        self.prepared = false;
     }
 
     pub fn add_data(&mut self, data: Value) -> Result<()> {
-        self.data.merge(data)
+        self.prepared = false;
+        self.interpreter.get_data_mut().merge(data)
     }
 
-    pub fn eval_query(&self, query: String, enable_tracing: bool) -> Result<QueryResults> {
-        // Analyze the modules and determine how statements must be scheduled.
-        let analyzer = Analyzer::new();
-        let schedule = analyzer.analyze(&self.modules)?;
+    pub fn get_modules(&mut self) -> &Vec<Ref<Module>> {
+        &self.modules
+    }
+
+    fn prepare_for_eval(&mut self, enable_tracing: bool) -> Result<()> {
+        self.interpreter.set_traces(enable_tracing);
+
+        // if the data/policies have changed or the interpreter has never been prepared
+        if !self.prepared {
+            // Analyze the modules and determine how statements must be scheduled.
+            let analyzer = Analyzer::new();
+            let schedule = analyzer.analyze(&self.modules)?;
+
+            self.interpreter.init_with_document()?;
+            self.interpreter.set_schedule(Some(schedule));
+            self.interpreter.set_modules(&self.modules);
+
+            self.interpreter.clear_builtins_cache();
+            // when the interpreter is prepared the initial data is saved
+            // the data will be reset to init_data each time clean_internal_evaluation_state is called
+            let init_data = self.interpreter.get_data_mut().clone();
+            self.interpreter.set_init_data(init_data);
+
+            self.interpreter
+                .set_functions(gather_functions(&self.modules)?);
+            self.interpreter.gather_rules()?;
+            self.prepared = true;
+        }
+
+        Ok(())
+    }
+
+    pub fn eval_rule(
+        &mut self,
+        module: &Ref<Module>,
+        rule: &Ref<Rule>,
+        enable_tracing: bool,
+    ) -> Result<Value> {
+        self.prepare_for_eval(enable_tracing)?;
+        self.interpreter.clean_internal_evaluation_state();
 
-        // Create interpreter object.
-        let mut interpreter = Interpreter::new(&self.modules)?;
+        self.interpreter.eval_rule(module, rule)?;
+
+        Ok(self.interpreter.get_data_mut().clone())
+    }
+
+    pub fn eval_modules(&mut self, enable_tracing: bool) -> Result<Value> {
+        self.prepare_for_eval(enable_tracing)?;
+        self.interpreter.clean_internal_evaluation_state();
+
+        // Ensure that each module has an empty object
+        for m in &self.modules {
+            let path = Parser::get_path_ref_components(&m.package.refr)?;
+            let path: Vec<&str> = path.iter().map(|s| *s.text()).collect();
+            let vref =
+                Interpreter::make_or_get_value_mut(self.interpreter.get_data_mut(), &path[..])?;
+            if *vref == Value::Undefined {
+                *vref = Value::new_object();
+            }
+        }
+
+        self.interpreter.check_default_rules()?;
+        for module in self.modules.clone() {
+            for rule in &module.policy {
+                self.interpreter.eval_rule(&module, rule)?;
+            }
+        }
+        // Defer the evaluation of the default rules to here
+        for module in self.modules.clone() {
+            let prev_module = self.interpreter.set_current_module(Some(module.clone()))?;
+            for rule in &module.policy {
+                self.interpreter.eval_default_rule(rule)?;
+            }
+            self.interpreter.set_current_module(prev_module)?;
+        }
+
+        Ok(self.interpreter.get_data_mut().clone())
+    }
 
-        // Evaluate all the modules.
-        interpreter.eval(
-            &Some(self.data.clone()),
-            &Some(self.input.clone()),
-            false,
-            Some(schedule),
-        )?;
+    pub fn eval_query(&mut self, query: String, enable_tracing: bool) -> Result<QueryResults> {
+        self.eval_modules(false)?;
 
         // Parse the query.
         let query_len = query.len();
@@ -88,7 +160,9 @@ impl Engine {
         let query_node = Ref::new(parser.parse_query(query_span, "")?);
         let query_schedule = Analyzer::new().analyze_query_snippet(&self.modules, &query_node)?;
 
-        let results = interpreter.eval_user_query(&query_node, &query_schedule, enable_tracing)?;
+        let results =
+            self.interpreter
+                .eval_user_query(&query_node, &query_schedule, enable_tracing)?;
         Ok(results)
     }
 }
diff --git a/src/interpreter.rs b/src/interpreter.rs
index efcbd08f..7c7f7c3f 100644
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -20,12 +20,12 @@ type Scope = BTreeMap<SourceStr, Value>;
 type DefaultRuleInfo = (Ref<Rule>, Option<String>);
 type ContextExprs = (Option<Ref<Expr>>, Option<Ref<Expr>>);
 
+#[derive(Clone)]
 pub struct Interpreter {
     modules: Vec<Ref<Module>>,
     module: Option<Ref<Module>>,
     schedule: Option<Schedule>,
     current_module_path: String,
-    prepared: bool,
     input: Value,
     data: Value,
     init_data: Value,
@@ -46,6 +46,12 @@ pub struct Interpreter {
     allow_deprecated: bool,
 }
 
+impl Default for Interpreter {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 #[derive(Debug, Clone, Serialize)]
 pub struct QueryResult {
     // Expressions is shown first to match OPA.
@@ -88,20 +94,16 @@ struct LoopExpr {
 }
 
 impl Interpreter {
-    pub fn new(modules: &[Ref<Module>]) -> Result<Interpreter> {
-        let mut with_document = Value::new_object();
-        *Self::make_or_get_value_mut(&mut with_document, &["data"])? = Value::new_object();
-        *Self::make_or_get_value_mut(&mut with_document, &["input"])? = Value::new_object();
-        Ok(Interpreter {
-            modules: modules.to_vec(),
+    pub fn new() -> Interpreter {
+        Interpreter {
+            modules: vec![],
             module: None,
             schedule: None,
             current_module_path: String::default(),
-            prepared: false,
             input: Value::new_object(),
             data: Value::new_object(),
             init_data: Value::new_object(),
-            with_document,
+            with_document: Value::new_object(),
             with_functions: BTreeMap::new(),
             scopes: vec![Scope::new()],
             contexts: vec![],
@@ -115,47 +117,68 @@ impl Interpreter {
             no_rules_lookup: false,
             traces: None,
             allow_deprecated: true,
-        })
+        }
+    }
+
+    pub fn set_schedule(&mut self, schedule: Option<Schedule>) {
+        self.schedule = schedule;
+    }
+
+    pub fn set_functions(&mut self, functions: FunctionTable) {
+        self.functions = functions;
     }
 
-    pub fn get_modules(&mut self) -> &mut Vec<Ref<Module>> {
+    pub fn set_modules(&mut self, modules: &[Ref<Module>]) {
+        self.modules = modules.to_vec();
+    }
+
+    pub fn get_modules_mut(&mut self) -> &mut Vec<Ref<Module>> {
         &mut self.modules
     }
 
+    pub fn set_init_data(&mut self, init_data: Value) {
+        self.init_data = init_data;
+    }
+
     pub fn set_data(&mut self, data: Value) {
         self.data = data;
     }
 
-    pub fn get_data(&mut self) -> &mut Value {
+    pub fn get_data_mut(&mut self) -> &mut Value {
         &mut self.data
     }
 
-    fn clean_internal_evaluation_state(&mut self) {
-        self.data = self.init_data.clone();
-        self.processed.clear();
-        self.loop_var_values.clear();
-        self.scopes = vec![Scope::new()];
-        self.contexts = vec![];
-    }
-
-    fn checks_for_eval(&mut self, input: &Option<Value>, enable_tracing: bool) -> Result<()> {
-        if !self.prepared {
-            bail!("prepare_for_eval should be called before eval_modules");
-        }
-
+    pub fn set_traces(&mut self, enable_tracing: bool) {
         self.traces = match enable_tracing {
             true => Some(vec![]),
             false => None,
         };
+    }
 
-        if let Some(input) = input {
-            self.input = input.clone();
-            info!("input: {:#?}", self.input);
-        }
+    pub fn set_input(&mut self, input: Value) {
+        self.input = input;
+        info!("input: {:#?}", self.input);
+    }
+
+    pub fn init_with_document(&mut self) -> Result<()> {
+        *Self::make_or_get_value_mut(&mut self.with_document, &["data"])? = Value::new_object();
+        *Self::make_or_get_value_mut(&mut self.with_document, &["input"])? = Value::new_object();
 
         Ok(())
     }
 
+    pub fn clear_builtins_cache(&mut self) {
+        self.builtins_cache.clear();
+    }
+
+    pub fn clean_internal_evaluation_state(&mut self) {
+        self.data = self.init_data.clone();
+        self.processed.clear();
+        self.loop_var_values.clear();
+        self.scopes = vec![Scope::new()];
+        self.contexts = vec![];
+    }
+
     fn current_module(&self) -> Result<Ref<Module>> {
         self.module
             .clone()
@@ -2039,7 +2062,7 @@ impl Interpreter {
     }
 
     #[inline]
-    fn make_or_get_value_mut<'a>(obj: &'a mut Value, paths: &[&str]) -> Result<&'a mut Value> {
+    pub fn make_or_get_value_mut<'a>(obj: &'a mut Value, paths: &[&str]) -> Result<&'a mut Value> {
         if paths.is_empty() {
             return Ok(obj);
         }
@@ -2107,7 +2130,10 @@ impl Interpreter {
         Ok(comps.join("."))
     }
 
-    fn set_current_module(&mut self, module: Option<Ref<Module>>) -> Result<Option<Ref<Module>>> {
+    pub fn set_current_module(
+        &mut self,
+        module: Option<Ref<Module>>,
+    ) -> Result<Option<Ref<Module>>> {
         let m = self.module.clone();
         if let Some(m) = &module {
             self.current_module_path = Self::get_path_string(&m.package.refr, Some("data"))?;
@@ -2172,7 +2198,7 @@ impl Interpreter {
         Err(span.error(format!("invalid `{kind}` in default value").as_str()))
     }
 
-    fn check_default_rules(&self) -> Result<()> {
+    pub fn check_default_rules(&self) -> Result<()> {
         for module in &self.modules {
             for rule in &module.policy {
                 if let Rule::Default { value, .. } = rule.as_ref() {
@@ -2183,7 +2209,7 @@ impl Interpreter {
         Ok(())
     }
 
-    fn eval_default_rule(&mut self, rule: &Ref<Rule>) -> Result<()> {
+    pub fn eval_default_rule(&mut self, rule: &Ref<Rule>) -> Result<()> {
         // Skip reprocessing rule.
         if self.processed.contains(rule) {
             return Ok(());
@@ -2264,7 +2290,7 @@ impl Interpreter {
         }
     }
 
-    fn eval_rule(&mut self, module: &Ref<Module>, rule: &Ref<Rule>) -> Result<()> {
+    pub fn eval_rule(&mut self, module: &Ref<Module>, rule: &Ref<Rule>) -> Result<()> {
         // Skip reprocessing rule
         if self.processed.contains(rule) {
             return Ok(());
@@ -2357,85 +2383,6 @@ impl Interpreter {
         }
     }
 
-    pub fn eval_rule_with_input(
-        &mut self,
-        module: &Ref<Module>,
-        rule: &Ref<Rule>,
-        input: &Option<Value>,
-        enable_tracing: bool,
-    ) -> Result<Value> {
-        self.checks_for_eval(input, enable_tracing)?;
-        self.clean_internal_evaluation_state();
-
-        self.eval_rule(module, rule)?;
-
-        Ok(self.data.clone())
-    }
-
-    pub fn prepare_for_eval(
-        &mut self,
-        schedule: Option<Schedule>,
-        data: &Option<Value>,
-    ) -> Result<()> {
-        self.schedule = schedule;
-        self.builtins_cache.clear();
-
-        if let Some(data) = data {
-            self.data = data.clone();
-            self.init_data = data.clone();
-        }
-
-        self.functions = gather_functions(&self.modules)?;
-
-        self.gather_rules()?;
-        self.prepared = true;
-
-        Ok(())
-    }
-
-    pub fn eval_modules(&mut self, input: &Option<Value>, enable_tracing: bool) -> Result<Value> {
-        self.checks_for_eval(input, enable_tracing)?;
-        self.clean_internal_evaluation_state();
-
-        // Ensure that each module has an empty object
-        for m in &self.modules {
-            let path = Parser::get_path_ref_components(&m.package.refr)?;
-            let path: Vec<&str> = path.iter().map(|s| *s.text()).collect();
-            let vref = Self::make_or_get_value_mut(&mut self.data, &path[..])?;
-            if *vref == Value::Undefined {
-                *vref = Value::new_object();
-            }
-        }
-
-        self.check_default_rules()?;
-        for module in self.modules.clone() {
-            for rule in &module.policy {
-                self.eval_rule(&module, rule)?;
-            }
-        }
-        // Defer the evaluation of the default rules to here
-        for module in self.modules.clone() {
-            let prev_module = self.set_current_module(Some(module.clone()))?;
-            for rule in &module.policy {
-                self.eval_default_rule(rule)?;
-            }
-            self.set_current_module(prev_module)?;
-        }
-
-        Ok(self.data.clone())
-    }
-
-    pub fn eval(
-        &mut self,
-        data: &Option<Value>,
-        input: &Option<Value>,
-        enable_tracing: bool,
-        schedule: Option<Schedule>,
-    ) -> Result<Value> {
-        self.prepare_for_eval(schedule, data)?;
-        self.eval_modules(input, enable_tracing)
-    }
-
     pub fn eval_user_query(
         &mut self,
         query: &Ref<Query>,
@@ -2503,7 +2450,7 @@ impl Interpreter {
         }
     }
 
-    fn gather_rules(&mut self) -> Result<()> {
+    pub fn gather_rules(&mut self) -> Result<()> {
         for module in self.modules.clone() {
             let prev_module = self.set_current_module(Some(module.clone()))?;
             for rule in &module.policy {
diff --git a/src/scheduler.rs b/src/scheduler.rs
index 7f70c4cd..0875bfd4 100644
--- a/src/scheduler.rs
+++ b/src/scheduler.rs
@@ -58,8 +58,7 @@ pub fn schedule<Str: Clone + std::cmp::Ord + std::fmt::Debug>(
     }
 
     // Order of execution for statements.
-    let mut order = vec![];
-    order.reserve(infos.len());
+    let mut order = Vec::with_capacity(infos.len());
 
     // Keep track of whether a var has been defined or not.
     let mut defined_vars = BTreeSet::new();
diff --git a/tests/interpreter/mod.rs b/tests/interpreter/mod.rs
index bf108382..57b6a7f4 100644
--- a/tests/interpreter/mod.rs
+++ b/tests/interpreter/mod.rs
@@ -192,10 +192,10 @@ pub fn eval_file(
     query: &str,
     enable_tracing: bool,
 ) -> Result<Vec<Value>> {
+    let mut engine: Engine = engine::Engine::new();
+
     let mut results = vec![];
     let mut files = vec![];
-    let mut sources = vec![];
-    let mut modules = vec![];
 
     for (idx, _) in regos.iter().enumerate() {
         files.push(format!("rego_{idx}"));
@@ -203,35 +203,15 @@ pub fn eval_file(
 
     for (idx, file) in files.iter().enumerate() {
         let contents = regos[idx].as_str();
-        sources.push(Source::new(file.to_string(), contents.to_string()));
+        engine.add_policy(file.to_string(), contents.to_string())?;
     }
 
-    for source in &sources {
-        let mut parser = Parser::new(source)?;
-        modules.push(Ref::new(parser.parse()?));
+    if let Some(data) = data_opt {
+        engine.add_data(data)?;
     }
 
-    let query_source = regorus::Source::new("<query.rego".to_string(), query.to_string());
-    let query_span = regorus::Span {
-        source: query_source.clone(),
-        line: 1,
-        col: 1,
-        start: 0,
-        end: query.len() as u16,
-    };
-    let mut parser = regorus::Parser::new(&query_source)?;
-    let query_node = Ref::new(parser.parse_query(query_span, "")?);
-    let query_schedule = regorus::Analyzer::new().analyze_query_snippet(&modules, &query_node)?;
-
-    let analyzer = Analyzer::new();
-    let schedule = analyzer.analyze(&modules)?;
-
-    let mut interpreter = interpreter::Interpreter::new(&modules)?;
     if let Some(input) = input_opt {
-        // if inputs are defined then first the evaluation if prepared
-        interpreter.prepare_for_eval(Some(schedule), &data_opt)?;
-
-        // then all modules are evaluated for each input
+        // all modules are evaluated for each input
         let mut inputs = vec![];
         match input {
             ValueOrVec::Single(single_input) => inputs.push(single_input),
@@ -239,21 +219,20 @@ pub fn eval_file(
         }
 
         for input in inputs {
-            interpreter.eval_modules(&Some(input), enable_tracing)?;
+            engine.set_input(input);
+            engine.eval_modules(enable_tracing)?;
 
             // Now eval the query.
             push_query_results(
-                interpreter.eval_user_query(&query_node, &query_schedule, enable_tracing)?,
+                engine.eval_query(query.to_string(), enable_tracing)?,
                 &mut results,
             );
         }
     } else {
         // it no input is defined then one evaluation of all modules is performed
-        interpreter.eval(&data_opt, &None, enable_tracing, Some(schedule))?;
-
         // Now eval the query.
         push_query_results(
-            interpreter.eval_user_query(&query_node, &query_schedule, enable_tracing)?,
+            engine.eval_query(query.to_string(), enable_tracing)?,
             &mut results,
         );
     }
diff --git a/tests/opa.rs b/tests/opa.rs
index 3d8e2f95..8ea2a6da 100644
--- a/tests/opa.rs
+++ b/tests/opa.rs
@@ -136,7 +136,7 @@ fn run_opa_tests(opa_tests_dir: String, folders: &[String]) -> Result<()> {
                     let path = Path::new("target/opa/failures").join(path_dir);
                     std::fs::create_dir_all(path.clone())?;
 
-                    let mut cmd = "cargo run --example dregorus eval".to_string();
+                    let mut cmd = "cargo run --example regorus eval".to_string();
                     if let Some(data) = &case.data {
                         let json_path = path.join(format!("data{n}.json"));
                         cmd += format!(" -d {}", json_path.display()).as_str();