diff --git a/nac3core/src/codegen/test.rs b/nac3core/src/codegen/test.rs
index 9649e68e..59f62129 100644
--- a/nac3core/src/codegen/test.rs
+++ b/nac3core/src/codegen/test.rs
@@ -28,7 +28,7 @@ use crate::{
         DefinitionId, FunInstance, TopLevelContext, TopLevelDef,
     },
     typecheck::{
-        type_inferencer::{FunctionData, Inferencer, PrimitiveStore},
+        type_inferencer::{FunctionData, IdentifierInfo, Inferencer, PrimitiveStore},
         typedef::{FunSignature, FuncArg, Type, TypeEnum, Unifier, VarMap},
     },
 };
@@ -141,7 +141,8 @@ fn test_primitives() {
     };
     let mut virtual_checks = Vec::new();
     let mut calls = HashMap::new();
-    let mut identifiers: HashSet<_> = ["a".into(), "b".into()].into();
+    let mut identifiers: HashMap<_, _> =
+        ["a".into(), "b".into()].map(|id| (id, IdentifierInfo::default())).into();
     let mut inferencer = Inferencer {
         top_level: &top_level,
         function_data: &mut function_data,
@@ -320,7 +321,8 @@ fn test_simple_call() {
     };
     let mut virtual_checks = Vec::new();
     let mut calls = HashMap::new();
-    let mut identifiers: HashSet<_> = ["a".into(), "foo".into()].into();
+    let mut identifiers: HashMap<_, _> =
+        ["a".into(), "foo".into()].map(|id| (id, IdentifierInfo::default())).into();
     let mut inferencer = Inferencer {
         top_level: &top_level,
         function_data: &mut function_data,
diff --git a/nac3core/src/toplevel/composer.rs b/nac3core/src/toplevel/composer.rs
index 06d5022b..020c7a8f 100644
--- a/nac3core/src/toplevel/composer.rs
+++ b/nac3core/src/toplevel/composer.rs
@@ -7,7 +7,7 @@ use crate::{
     codegen::{expr::get_subst_key, stmt::exn_constructor},
     symbol_resolver::SymbolValue,
     typecheck::{
-        type_inferencer::{FunctionData, Inferencer},
+        type_inferencer::{FunctionData, IdentifierInfo, Inferencer},
         typedef::{TypeVar, VarMap},
     },
 };
@@ -2057,11 +2057,12 @@ impl TopLevelComposer {
                         })
                     };
                     let mut identifiers = {
-                        let mut result: HashSet<_> = HashSet::new();
+                        let mut result = HashMap::new();
                         if self_type.is_some() {
-                            result.insert("self".into());
+                            result.insert("self".into(), IdentifierInfo::default());
                         }
-                        result.extend(inst_args.iter().map(|x| x.name));
+                        result
+                            .extend(inst_args.iter().map(|x| (x.name, IdentifierInfo::default())));
                         result
                     };
                     let mut calls: HashMap<CodeLocation, CallId> = HashMap::new();
diff --git a/nac3core/src/typecheck/function_check.rs b/nac3core/src/typecheck/function_check.rs
index 9dd84091..4b5ccb57 100644
--- a/nac3core/src/typecheck/function_check.rs
+++ b/nac3core/src/typecheck/function_check.rs
@@ -1,4 +1,7 @@
-use std::{collections::HashSet, iter::once};
+use std::{
+    collections::{HashMap, HashSet},
+    iter::once,
+};
 
 use nac3parser::ast::{
     self, Constant, Expr, ExprKind,
@@ -7,7 +10,7 @@ use nac3parser::ast::{
 };
 
 use super::{
-    type_inferencer::Inferencer,
+    type_inferencer::{IdentifierInfo, Inferencer},
     typedef::{Type, TypeEnum},
 };
 use crate::toplevel::helper::PrimDef;
@@ -24,15 +27,15 @@ impl<'a> Inferencer<'a> {
     fn check_pattern(
         &mut self,
         pattern: &Expr<Option<Type>>,
-        defined_identifiers: &mut HashSet<StrRef>,
+        defined_identifiers: &mut HashMap<StrRef, IdentifierInfo>,
     ) -> Result<(), HashSet<String>> {
         match &pattern.node {
             ExprKind::Name { id, .. } if id == &"none".into() => {
                 Err(HashSet::from([format!("cannot assign to a `none` (at {})", pattern.location)]))
             }
             ExprKind::Name { id, .. } => {
-                if !defined_identifiers.contains(id) {
-                    defined_identifiers.insert(*id);
+                if !defined_identifiers.contains_key(id) {
+                    defined_identifiers.insert(*id, IdentifierInfo::default());
                 }
                 self.should_have_value(pattern)?;
                 Ok(())
@@ -72,7 +75,7 @@ impl<'a> Inferencer<'a> {
     fn check_expr(
         &mut self,
         expr: &Expr<Option<Type>>,
-        defined_identifiers: &mut HashSet<StrRef>,
+        defined_identifiers: &mut HashMap<StrRef, IdentifierInfo>,
     ) -> Result<(), HashSet<String>> {
         // there are some cases where the custom field is None
         if let Some(ty) = &expr.custom {
@@ -93,7 +96,7 @@ impl<'a> Inferencer<'a> {
                     return Ok(());
                 }
                 self.should_have_value(expr)?;
-                if !defined_identifiers.contains(id) {
+                if !defined_identifiers.contains_key(id) {
                     match self.function_data.resolver.get_symbol_type(
                         self.unifier,
                         &self.top_level.definitions.read(),
@@ -101,7 +104,7 @@ impl<'a> Inferencer<'a> {
                         *id,
                     ) {
                         Ok(_) => {
-                            self.defined_identifiers.insert(*id);
+                            self.defined_identifiers.insert(*id, IdentifierInfo::default());
                         }
                         Err(e) => {
                             return Err(HashSet::from([format!(
@@ -174,9 +177,7 @@ impl<'a> Inferencer<'a> {
                 let mut defined_identifiers = defined_identifiers.clone();
                 for arg in &args.args {
                     // TODO: should we check the types here?
-                    if !defined_identifiers.contains(&arg.node.arg) {
-                        defined_identifiers.insert(arg.node.arg);
-                    }
+                    defined_identifiers.entry(arg.node.arg).or_default();
                 }
                 self.check_expr(body, &mut defined_identifiers)?;
             }
@@ -239,7 +240,7 @@ impl<'a> Inferencer<'a> {
     fn check_stmt(
         &mut self,
         stmt: &Stmt<Option<Type>>,
-        defined_identifiers: &mut HashSet<StrRef>,
+        defined_identifiers: &mut HashMap<StrRef, IdentifierInfo>,
     ) -> Result<bool, HashSet<String>> {
         match &stmt.node {
             StmtKind::For { target, iter, body, orelse, .. } => {
@@ -265,9 +266,11 @@ impl<'a> Inferencer<'a> {
                 let body_returned = self.check_block(body, &mut body_identifiers)?;
                 let orelse_returned = self.check_block(orelse, &mut orelse_identifiers)?;
 
-                for ident in &body_identifiers {
-                    if !defined_identifiers.contains(ident) && orelse_identifiers.contains(ident) {
-                        defined_identifiers.insert(*ident);
+                for ident in body_identifiers.keys() {
+                    if !defined_identifiers.contains_key(ident)
+                        && orelse_identifiers.contains_key(ident)
+                    {
+                        defined_identifiers.insert(*ident, IdentifierInfo::default());
                     }
                 }
                 Ok(body_returned && orelse_returned)
@@ -298,7 +301,7 @@ impl<'a> Inferencer<'a> {
                     let mut defined_identifiers = defined_identifiers.clone();
                     let ast::ExcepthandlerKind::ExceptHandler { name, body, .. } = &handler.node;
                     if let Some(name) = name {
-                        defined_identifiers.insert(*name);
+                        defined_identifiers.insert(*name, IdentifierInfo::default());
                     }
                     self.check_block(body, &mut defined_identifiers)?;
                 }
@@ -370,7 +373,7 @@ impl<'a> Inferencer<'a> {
     pub fn check_block(
         &mut self,
         block: &[Stmt<Option<Type>>],
-        defined_identifiers: &mut HashSet<StrRef>,
+        defined_identifiers: &mut HashMap<StrRef, IdentifierInfo>,
     ) -> Result<bool, HashSet<String>> {
         let mut ret = false;
         for stmt in block {
diff --git a/nac3core/src/typecheck/type_inferencer/mod.rs b/nac3core/src/typecheck/type_inferencer/mod.rs
index 48736738..ba09bd5a 100644
--- a/nac3core/src/typecheck/type_inferencer/mod.rs
+++ b/nac3core/src/typecheck/type_inferencer/mod.rs
@@ -88,6 +88,20 @@ impl PrimitiveStore {
     }
 }
 
+/// Information regarding a defined identifier.
+#[derive(Clone, Copy, Debug, Default)]
+pub struct IdentifierInfo {
+    /// Whether this identifier refers to a global variable.
+    pub is_global: bool,
+}
+
+impl IdentifierInfo {
+    #[must_use]
+    pub fn new() -> IdentifierInfo {
+        IdentifierInfo::default()
+    }
+}
+
 pub struct FunctionData {
     pub resolver: Arc<dyn SymbolResolver + Send + Sync>,
     pub return_type: Option<Type>,
@@ -96,7 +110,7 @@ pub struct FunctionData {
 
 pub struct Inferencer<'a> {
     pub top_level: &'a TopLevelContext,
-    pub defined_identifiers: HashSet<StrRef>,
+    pub defined_identifiers: HashMap<StrRef, IdentifierInfo>,
     pub function_data: &'a mut FunctionData,
     pub unifier: &'a mut Unifier,
     pub primitives: &'a PrimitiveStore,
@@ -228,9 +242,7 @@ impl<'a> Fold<()> for Inferencer<'a> {
                                 handler.location,
                             ));
                             if let Some(name) = name {
-                                if !self.defined_identifiers.contains(&name) {
-                                    self.defined_identifiers.insert(name);
-                                }
+                                self.defined_identifiers.entry(name).or_default();
                                 if let Some(old_typ) = self.variable_mapping.insert(name, typ) {
                                     let loc = handler.location;
                                     self.unifier.unify(old_typ, typ).map_err(|e| {
@@ -553,7 +565,7 @@ impl<'a> Fold<()> for Inferencer<'a> {
                         unreachable!("must be tobj")
                     }
                 } else {
-                    if !self.defined_identifiers.contains(id) {
+                    if !self.defined_identifiers.contains_key(id) {
                         match self.function_data.resolver.get_symbol_type(
                             self.unifier,
                             &self.top_level.definitions.read(),
@@ -561,7 +573,7 @@ impl<'a> Fold<()> for Inferencer<'a> {
                             *id,
                         ) {
                             Ok(_) => {
-                                self.defined_identifiers.insert(*id);
+                                self.defined_identifiers.insert(*id, IdentifierInfo::default());
                             }
                             Err(e) => {
                                 return report_error(
@@ -626,8 +638,8 @@ impl<'a> Inferencer<'a> {
     fn infer_pattern<T>(&mut self, pattern: &ast::Expr<T>) -> Result<(), InferenceError> {
         match &pattern.node {
             ExprKind::Name { id, .. } => {
-                if !self.defined_identifiers.contains(id) {
-                    self.defined_identifiers.insert(*id);
+                if !self.defined_identifiers.contains_key(id) {
+                    self.defined_identifiers.insert(*id, IdentifierInfo::default());
                 }
                 Ok(())
             }
@@ -736,8 +748,8 @@ impl<'a> Inferencer<'a> {
         let mut defined_identifiers = self.defined_identifiers.clone();
         for arg in &args.args {
             let name = &arg.node.arg;
-            if !defined_identifiers.contains(name) {
-                defined_identifiers.insert(*name);
+            if !defined_identifiers.contains_key(name) {
+                defined_identifiers.insert(*name, IdentifierInfo::default());
             }
         }
         let fn_args: Vec<_> = args
diff --git a/nac3core/src/typecheck/type_inferencer/test.rs b/nac3core/src/typecheck/type_inferencer/test.rs
index f81e4ca4..a3e307f4 100644
--- a/nac3core/src/typecheck/type_inferencer/test.rs
+++ b/nac3core/src/typecheck/type_inferencer/test.rs
@@ -519,7 +519,7 @@ impl TestEnvironment {
             primitives: &mut self.primitives,
             virtual_checks: &mut self.virtual_checks,
             calls: &mut self.calls,
-            defined_identifiers: HashSet::default(),
+            defined_identifiers: HashMap::default(),
             in_handler: false,
         }
     }
@@ -595,8 +595,9 @@ fn test_basic(source: &str, mapping: &HashMap<&str, &str>, virtuals: &[(&str, &s
     println!("source:\n{source}");
     let mut env = TestEnvironment::new();
     let id_to_name = std::mem::take(&mut env.id_to_name);
-    let mut defined_identifiers: HashSet<_> = env.identifier_mapping.keys().copied().collect();
-    defined_identifiers.insert("virtual".into());
+    let mut defined_identifiers: HashMap<_, _> =
+        env.identifier_mapping.keys().copied().map(|id| (id, IdentifierInfo::default())).collect();
+    defined_identifiers.insert("virtual".into(), IdentifierInfo::default());
     let mut inferencer = env.get_inferencer();
     inferencer.defined_identifiers.clone_from(&defined_identifiers);
     let statements = parse_program(source, FileName::default()).unwrap();
@@ -741,8 +742,9 @@ fn test_primitive_magic_methods(source: &str, mapping: &HashMap<&str, &str>) {
     println!("source:\n{source}");
     let mut env = TestEnvironment::basic_test_env();
     let id_to_name = std::mem::take(&mut env.id_to_name);
-    let mut defined_identifiers: HashSet<_> = env.identifier_mapping.keys().copied().collect();
-    defined_identifiers.insert("virtual".into());
+    let mut defined_identifiers: HashMap<_, _> =
+        env.identifier_mapping.keys().copied().map(|id| (id, IdentifierInfo::default())).collect();
+    defined_identifiers.insert("virtual".into(), IdentifierInfo::default());
     let mut inferencer = env.get_inferencer();
     inferencer.defined_identifiers.clone_from(&defined_identifiers);
     let statements = parse_program(source, FileName::default()).unwrap();