diff --git a/nac3core/src/typecheck/escape_analysis/lifetime.rs b/nac3core/src/typecheck/escape_analysis/lifetime.rs
new file mode 100644
index 00000000..97664387
--- /dev/null
+++ b/nac3core/src/typecheck/escape_analysis/lifetime.rs
@@ -0,0 +1,276 @@
+use std::cell::RefCell;
+use std::collections::{HashMap, HashSet};
+use std::rc::Rc;
+
+use crate::typecheck::unification_table::{UnificationKey, UnificationTable};
+
+use itertools::Itertools;
+use nac3parser::ast::StrRef;
+
+// change this to enum, only local needs unification key
+pub type Lifetime = UnificationKey;
+
+#[derive(Copy, Debug, Clone, PartialEq, Eq, Hash)]
+pub enum LifetimeKind {
+    // can be assigned to fields of anything
+    // can be returned
+    // lifetime of static values
+    Global,
+    // can only be assigned to fields of objects with local lifetime
+    // can be returned
+    // lifetime of parameters
+    NonLocal,
+    // can only be assigned to fields of objects with local lifetime
+    // cannot be returned
+    // lifetime of constructor return values
+    Local,
+    // can only be assigned to fields of objects with local lifetime
+    // cannot be returned
+    // lifetime of function return values
+    Unknown,
+}
+
+impl std::ops::BitAnd for LifetimeKind {
+    type Output = Self;
+
+    fn bitand(self, other: Self) -> Self {
+        use LifetimeKind::*;
+        match (self, other) {
+            (x, y) if x == y => x,
+            (Global, NonLocal) | (NonLocal, Global) => NonLocal,
+            _ => Unknown,
+        }
+    }
+}
+
+impl std::cmp::PartialOrd for LifetimeKind {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        use LifetimeKind::*;
+        match (*self, *other) {
+            (x, y) if x == y => Some(std::cmp::Ordering::Equal),
+            (Local, _) | (_, Global) => Some(std::cmp::Ordering::Less),
+            (_, Local) | (Global, _) => Some(std::cmp::Ordering::Greater),
+            _ => None,
+        }
+    }
+}
+
+pub struct BlockLifetimeContext {
+    mapping: Vec<(Option<Lifetime>, Lifetime)>,
+}
+
+impl BlockLifetimeContext {
+    pub fn new() -> Self {
+        BlockLifetimeContext { mapping: Vec::new() }
+    }
+
+    pub fn add_fresh(&mut self, lifetime: Lifetime) {
+        self.mapping.push((None, lifetime));
+    }
+}
+
+struct LifetimeEntry {
+    kind: LifetimeKind,
+    fields: RefCell<HashMap<StrRef, Lifetime>>,
+}
+
+pub struct LifetimeTable {
+    table: UnificationTable<Rc<LifetimeEntry>>,
+    cache: HashSet<(Lifetime, Lifetime)>,
+}
+
+impl LifetimeTable {
+    pub fn new() -> Self {
+        let mut zelf = Self { table: UnificationTable::new(), cache: Default::default() };
+        zelf.table.new_key(Rc::new(LifetimeEntry {
+            kind: LifetimeKind::Unknown,
+            fields: Default::default(),
+        }));
+        zelf
+    }
+
+    pub fn add_lifetime(&mut self, kind: LifetimeKind) -> Lifetime {
+        self.table.new_key(Rc::new(LifetimeEntry { kind, fields: Default::default() }))
+    }
+
+    pub fn unify(&mut self, a: Lifetime, b: Lifetime, ctx: &mut BlockLifetimeContext) {
+        self.cache.clear();
+        self.unify_impl(a, b, ctx);
+    }
+
+    fn get_scoped<const N: usize>(
+        &mut self,
+        mut lifetimes: [Lifetime; N],
+        ctx: &mut BlockLifetimeContext,
+    ) -> [Lifetime; N] {
+        for l in lifetimes.iter_mut() {
+            let mut result = None;
+            for (k, v) in ctx.mapping.iter() {
+                if self.table.unioned(*v, *l) || k.map_or(false, |k| self.table.unioned(k, *l)) {
+                    // already fresh
+                    result = Some(*v);
+                    break;
+                }
+            }
+            if let Some(result) = result {
+                *l = result;
+            } else {
+                let lifetime = self.table.probe_value(*l).clone();
+                *l = if lifetime.kind == LifetimeKind::Unknown {
+                    UnificationKey(0)
+                } else {
+                    let k = self.table.new_key(lifetime);
+                    ctx.mapping.push((Some(*l), k));
+                    k
+                }
+            }
+        }
+        lifetimes
+    }
+
+    fn unify_impl(&mut self, a: Lifetime, b: Lifetime, ctx: &mut BlockLifetimeContext) {
+        use LifetimeKind::*;
+
+        let [a, b] = self.get_scoped([a, b], ctx);
+        let a = self.table.get_representative(a);
+        let b = self.table.get_representative(b);
+        if a == b || self.cache.contains(&(a, b)) || self.cache.contains(&(b, a)) {
+            return;
+        }
+        self.cache.insert((a, b));
+
+        let v_a = self.table.probe_value(a).clone();
+        let v_b = self.table.probe_value(b).clone();
+
+        let result_kind = v_a.kind & v_b.kind;
+
+        let fields = if result_kind == Local {
+            // we only need to track fields lifetime for objects with local lifetime
+            let fields = v_a.fields.clone();
+            {
+                let mut fields_ref = fields.borrow_mut();
+                for (k, v) in v_b.fields.borrow().iter() {
+                    if let Some(old) = fields_ref.insert(k.clone(), *v) {
+                        self.unify_impl(old, *v, ctx);
+                    }
+                }
+            }
+            fields
+        } else {
+            Default::default()
+        };
+
+        self.table.unify(a, b);
+        self.table.set_value(a, Rc::new(LifetimeEntry { kind: result_kind, fields }));
+    }
+
+    pub fn get_field_lifetime(
+        &mut self,
+        lifetime: Lifetime,
+        field: StrRef,
+        ctx: &mut BlockLifetimeContext,
+    ) -> Lifetime {
+        use LifetimeKind::*;
+        let [lifetime] = self.get_scoped([lifetime], ctx);
+        if let LifetimeEntry { kind: Local, fields } = &*self.table.probe_value(lifetime).clone() {
+            if let Some(lifetime) = fields.borrow().get(&field) {
+                *lifetime
+            } else {
+                // unknown lifetime
+                // we can reuse this lifetime because it will never be unified to something else
+                UnificationKey(0)
+            }
+        } else {
+            lifetime
+        }
+    }
+
+    pub fn set_field_lifetime(
+        &mut self,
+        obj: Lifetime,
+        field: StrRef,
+        lifetime: Lifetime,
+        is_strong_update: bool,
+        ctx: &mut BlockLifetimeContext,
+    ) -> Result<(), String> {
+        let [obj, lifetime] = self.get_scoped([obj, lifetime], ctx);
+        let obj_lifetime = self.table.probe_value(obj).clone();
+        let field_lifetime = self.table.probe_value(lifetime).clone();
+        if !(obj_lifetime.kind <= field_lifetime.kind) {
+            return Err("lifetime error".to_string());
+        }
+        let mut fields = obj_lifetime.fields.borrow_mut();
+        if is_strong_update {
+            fields.insert(field, lifetime);
+        } else {
+            if let Some(old) = fields.insert(field, lifetime) {
+                self.unify(old, lifetime, ctx);
+            }
+        }
+        Ok(())
+    }
+
+    pub fn get_lifetime_kind(
+        &mut self,
+        lifetime: Lifetime,
+        ctx: &mut BlockLifetimeContext,
+    ) -> LifetimeKind {
+        let [lifetime] = self.get_scoped([lifetime], ctx);
+        self.table.probe_value(lifetime).kind
+    }
+
+    pub fn set_function_params(&mut self, lifetime: Lifetime, ctx: &mut BlockLifetimeContext) {
+        use LifetimeKind::*;
+        // unify each field with global
+        let [lifetime] = self.get_scoped([lifetime], ctx);
+        let lifetime = self.table.probe_value(lifetime).clone();
+        let mut worklist = lifetime.fields.borrow().values().copied().collect_vec();
+        while let Some(item) = worklist.pop() {
+            let [item] = self.get_scoped([item], ctx);
+            let lifetime = self.table.probe_value(item).clone();
+            if lifetime.kind == Unknown || lifetime.kind == Global {
+                continue;
+            }
+            let fields = lifetime.fields.borrow().clone();
+            for (_, v) in fields.iter() {
+                worklist.push(*v);
+            }
+            self.table.set_value(
+                item,
+                Rc::new(LifetimeEntry {
+                    kind: lifetime.kind & Global,
+                    fields: RefCell::new(fields),
+                }),
+            );
+        }
+    }
+
+    pub fn get_unknown_lifetime(&self) -> Lifetime {
+        UnificationKey(0)
+    }
+
+    pub fn equiv(&mut self, a: Lifetime, b: Lifetime, ctx: &mut BlockLifetimeContext) -> bool {
+        use LifetimeKind::Local;
+        let [a, b] = self.get_scoped([a, b], ctx);
+        if self.table.unioned(a, b) {
+            return true;
+        }
+        let lifetime_a = self.table.probe_value(a).clone();
+        let lifetime_b = self.table.probe_value(b).clone();
+        if lifetime_a.kind == Local && lifetime_b.kind == Local {
+            let fields_a = lifetime_a.fields.borrow();
+            let fields_b = lifetime_b.fields.borrow();
+            for (k, v) in fields_a.iter() {
+                if fields_b.get(k).map(|v1| self.equiv(*v, *v1, ctx)) != Some(true) {
+                    return false;
+                }
+            }
+            // they are just equivalent
+            // this can avoid infinite recursion
+            self.table.unify(a, b);
+            true
+        } else {
+            lifetime_a.kind == lifetime_b.kind
+        }
+    }
+}
diff --git a/nac3core/src/typecheck/escape_analysis/mod.rs b/nac3core/src/typecheck/escape_analysis/mod.rs
new file mode 100644
index 00000000..d33ca4b8
--- /dev/null
+++ b/nac3core/src/typecheck/escape_analysis/mod.rs
@@ -0,0 +1,317 @@
+use std::{collections::HashMap, sync::Arc};
+
+use nac3parser::ast::{Constant, Expr, ExprKind, StrRef};
+
+use crate::{
+    symbol_resolver::SymbolResolver,
+    toplevel::{TopLevelContext, TopLevelDef},
+};
+
+use self::lifetime::{BlockLifetimeContext, Lifetime, LifetimeTable};
+
+use super::{
+    type_inferencer::PrimitiveStore,
+    typedef::{Type, TypeEnum, Unifier},
+};
+
+pub mod lifetime;
+
+struct LifetimeContext<'a> {
+    variable_mapping: HashMap<StrRef, (Lifetime, bool)>,
+    scope_ctx: BlockLifetimeContext,
+    lifetime_table: LifetimeTable,
+    primitive_store: PrimitiveStore,
+    unifier: &'a mut Unifier,
+    resolver: Arc<dyn SymbolResolver + Send + Sync>,
+    top_level: &'a TopLevelContext,
+}
+
+impl<'a> LifetimeContext<'a> {
+    pub fn new(
+        unifier: &'a mut Unifier,
+        primitive_store: PrimitiveStore,
+        resolver: Arc<dyn SymbolResolver + Send + Sync>,
+        top_level: &'a TopLevelContext,
+    ) -> LifetimeContext<'a> {
+        LifetimeContext {
+            variable_mapping: HashMap::new(),
+            scope_ctx: BlockLifetimeContext::new(),
+            lifetime_table: LifetimeTable::new(),
+            primitive_store,
+            unifier,
+            resolver,
+            top_level,
+        }
+    }
+
+    fn get_expr_lifetime(
+        &mut self,
+        expr: &Expr<Option<Type>>,
+    ) -> Result<Option<(Lifetime, bool)>, String> {
+        let ty = expr.custom.unwrap();
+        let is_primitive = self.unifier.unioned(ty, self.primitive_store.int32)
+            || self.unifier.unioned(ty, self.primitive_store.int64)
+            || self.unifier.unioned(ty, self.primitive_store.uint32)
+            || self.unifier.unioned(ty, self.primitive_store.uint64)
+            || self.unifier.unioned(ty, self.primitive_store.float)
+            || self.unifier.unioned(ty, self.primitive_store.bool)
+            || self.unifier.unioned(ty, self.primitive_store.none)
+            || self.unifier.unioned(ty, self.primitive_store.range);
+
+        Ok(match &expr.node {
+            ExprKind::Name { id, .. } => {
+                if let Some(lifetime) = self.variable_mapping.get(id) {
+                    Some(*lifetime)
+                } else {
+                    if is_primitive {
+                        None
+                    } else {
+                        let lifetime =
+                            self.lifetime_table.add_lifetime(lifetime::LifetimeKind::Global);
+                        self.variable_mapping.insert(id.clone(), (lifetime, false));
+                        Some((lifetime, false))
+                    }
+                }
+            }
+            ExprKind::Attribute { value, attr, .. } => {
+                if is_primitive {
+                    self.get_expr_lifetime(value)?;
+                    None
+                } else {
+                    self.get_expr_lifetime(value)?.map(|lifetime| {
+                        (
+                            self.lifetime_table.get_field_lifetime(
+                                lifetime.0,
+                                *attr,
+                                &mut self.scope_ctx,
+                            ),
+                            false, // not sure if it is strong update for now...
+                        )
+                    })
+                }
+            }
+            ExprKind::Constant { .. } => {
+                if is_primitive {
+                    None
+                } else {
+                    Some((self.lifetime_table.add_lifetime(lifetime::LifetimeKind::Global), false))
+                }
+            }
+            ExprKind::List { elts, .. } => {
+                let elems =
+                    elts.iter()
+                        .map(|expr| self.get_expr_lifetime(expr))
+                        .collect::<Result<Vec<_>, _>>()?;
+                let elem = elems.into_iter().reduce(|prev, next| {
+                    if prev.is_some() {
+                        self.lifetime_table.unify(
+                            prev.unwrap().0,
+                            next.unwrap().0,
+                            &mut self.scope_ctx,
+                        );
+                    }
+                    prev
+                });
+                let list_lifetime = self.lifetime_table.add_lifetime(lifetime::LifetimeKind::Local);
+
+                if let Some(Some(elem)) = elem {
+                    self.lifetime_table
+                        .set_field_lifetime(
+                            list_lifetime,
+                            "elem".into(),
+                            elem.0,
+                            true,
+                            &mut self.scope_ctx,
+                        )
+                        .unwrap();
+                }
+                Some((list_lifetime, true))
+            }
+            ExprKind::Subscript { value, slice, .. } => {
+                // value must be a list, so lifetime cannot be None
+                let (value_lifetime, _) = self.get_expr_lifetime(value)?.unwrap();
+                match &slice.node {
+                    ExprKind::Slice { lower, upper, step } => {
+                        for expr in [lower, upper, step].iter().filter_map(|x| x.as_ref()) {
+                            // account for side effects when computing the slice
+                            self.get_expr_lifetime(expr)?;
+                        }
+                        Some((
+                            self.lifetime_table.add_lifetime(lifetime::LifetimeKind::Local),
+                            true,
+                        ))
+                    }
+                    ExprKind::Constant { value: Constant::Int(v), .. } => {
+                        if is_primitive {
+                            None
+                        } else if let TypeEnum::TList { .. } =
+                            &*self.unifier.get_ty(value.custom.unwrap())
+                        {
+                            Some((
+                                self.lifetime_table.get_field_lifetime(
+                                    value_lifetime,
+                                    "elem".into(),
+                                    &mut self.scope_ctx,
+                                ),
+                                false,
+                            ))
+                        } else {
+                            // tuple
+                            Some((
+                                self.lifetime_table.get_field_lifetime(
+                                    value_lifetime,
+                                    format!("elem{}", v).into(),
+                                    &mut self.scope_ctx,
+                                ),
+                                false,
+                            ))
+                        }
+                    }
+                    _ => {
+                        // account for side effects when computing the index
+                        self.get_expr_lifetime(slice)?;
+                        if is_primitive {
+                            None
+                        } else {
+                            Some((
+                                self.lifetime_table.get_field_lifetime(
+                                    value_lifetime,
+                                    "elem".into(),
+                                    &mut self.scope_ctx,
+                                ),
+                                false,
+                            ))
+                        }
+                    }
+                }
+            }
+            ExprKind::Tuple { elts, .. } => {
+                let elems =
+                    elts.iter()
+                        .map(|expr| self.get_expr_lifetime(expr))
+                        .collect::<Result<Vec<_>, _>>()?;
+                let tuple_lifetime =
+                    self.lifetime_table.add_lifetime(lifetime::LifetimeKind::Local);
+                for (i, lifetime) in elems.into_iter().enumerate() {
+                    if let Some((lifetime, _)) = lifetime {
+                        self.lifetime_table
+                            .set_field_lifetime(
+                                tuple_lifetime,
+                                format!("elem{}", i).into(),
+                                lifetime,
+                                true,
+                                &mut self.scope_ctx,
+                            )
+                            .unwrap();
+                    }
+                }
+                Some((tuple_lifetime, true))
+            }
+            ExprKind::Call { func, args, keywords } => {
+                let mut lifetimes = Vec::new();
+                for arg in args.iter() {
+                    if let Some(lifetime) = self.get_expr_lifetime(arg)? {
+                        lifetimes.push(lifetime.0);
+                    }
+                }
+                for keyword in keywords.iter() {
+                    if let Some(lifetime) = self.get_expr_lifetime(&keyword.node.value)? {
+                        lifetimes.push(lifetime.0);
+                    }
+                }
+                match &func.node {
+                    ExprKind::Name { id, .. } => {
+                        for lifetime in lifetimes.into_iter() {
+                            self.lifetime_table.set_function_params(lifetime, &mut self.scope_ctx);
+                        }
+                        if is_primitive {
+                            None
+                        } else {
+                            let id = self
+                                .resolver
+                                .get_identifier_def(*id)
+                                .map_err(|e| format!("{} (at {})", e, func.location))?;
+                            // constructors
+                            if let TopLevelDef::Class { .. } =
+                                &*self.top_level.definitions.read()[id.0].read()
+                            {
+                                Some((
+                                    self.lifetime_table.add_lifetime(lifetime::LifetimeKind::Local),
+                                    true,
+                                ))
+                            } else {
+                                Some((self.lifetime_table.get_unknown_lifetime(), false))
+                            }
+                        }
+                    }
+                    ExprKind::Attribute { value, .. } => {
+                        if let Some(lifetime) = self.get_expr_lifetime(value)? {
+                            lifetimes.push(lifetime.0);
+                        }
+                        for lifetime in lifetimes.into_iter() {
+                            self.lifetime_table.set_function_params(lifetime, &mut self.scope_ctx);
+                        }
+                        if is_primitive {
+                            None
+                        } else {
+                            Some((self.lifetime_table.get_unknown_lifetime(), false))
+                        }
+                    }
+                    _ => unimplemented!(),
+                }
+            }
+            ExprKind::BinOp { left, right, .. } => {
+                let mut lifetimes = Vec::new();
+                if let Some(l) = self.get_expr_lifetime(left)? {
+                    lifetimes.push(l.0);
+                }
+                if let Some(l) = self.get_expr_lifetime(right)? {
+                    lifetimes.push(l.0);
+                }
+                for lifetime in lifetimes.into_iter() {
+                    self.lifetime_table.set_function_params(lifetime, &mut self.scope_ctx);
+                }
+                if is_primitive {
+                    None
+                } else {
+                    Some((self.lifetime_table.get_unknown_lifetime(), false))
+                }
+            }
+            ExprKind::BoolOp { values, .. } => {
+                for v in values {
+                    self.get_expr_lifetime(v)?;
+                }
+                None
+            }
+            ExprKind::UnaryOp { operand, .. } => {
+                if let Some(l) = self.get_expr_lifetime(operand)? {
+                    self.lifetime_table.set_function_params(l.0, &mut self.scope_ctx);
+                }
+                if is_primitive {
+                    None
+                } else {
+                    Some((self.lifetime_table.get_unknown_lifetime(), false))
+                }
+            }
+            ExprKind::Compare { left,  comparators, .. } => {
+                let mut lifetimes = Vec::new();
+                if let Some(l) = self.get_expr_lifetime(left)? {
+                    lifetimes.push(l.0);
+                }
+                for c in comparators {
+                    if let Some(l) = self.get_expr_lifetime(c)? {
+                        lifetimes.push(l.0);
+                    }
+                }
+                for lifetime in lifetimes.into_iter() {
+                    self.lifetime_table.set_function_params(lifetime, &mut self.scope_ctx);
+                }
+                // compare should give bool output, which does not have lifetime
+                None
+            }
+            // TODO: listcomp, ifexpr
+            _ => unimplemented!(),
+        })
+
+    }
+}
diff --git a/nac3core/src/typecheck/mod.rs b/nac3core/src/typecheck/mod.rs
index 4cac1bf0..1b349230 100644
--- a/nac3core/src/typecheck/mod.rs
+++ b/nac3core/src/typecheck/mod.rs
@@ -4,3 +4,4 @@ pub mod type_error;
 pub mod type_inferencer;
 pub mod typedef;
 mod unification_table;
+pub mod escape_analysis;
diff --git a/nac3core/src/typecheck/unification_table.rs b/nac3core/src/typecheck/unification_table.rs
index 101057c5..adb0a11d 100644
--- a/nac3core/src/typecheck/unification_table.rs
+++ b/nac3core/src/typecheck/unification_table.rs
@@ -3,7 +3,7 @@ use std::rc::Rc;
 use itertools::izip;
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
-pub struct UnificationKey(usize);
+pub struct UnificationKey(pub(crate) usize);
 
 #[derive(Clone)]
 pub struct UnificationTable<V> {
@@ -44,6 +44,12 @@ impl<V> UnificationTable<V> {
         UnificationTable { parents: Vec::new(), ranks: Vec::new(), values: Vec::new(), log: Vec::new(), generation: 0 }
     }
 
+    fn log_action(&mut self, action: Action<V>) {
+        if !self.log.is_empty() {
+            self.log.push(action);
+        }
+    }
+
     pub fn new_key(&mut self, v: V) -> UnificationKey {
         let index = self.parents.len();
         self.parents.push(index);
@@ -61,10 +67,10 @@ impl<V> UnificationTable<V> {
         if self.ranks[a] < self.ranks[b] {
             std::mem::swap(&mut a, &mut b);
         }
-        self.log.push(Action::Parent { key: b, original_parent: self.parents[b] });
+        self.log_action(Action::Parent { key: b, original_parent: self.parents[b] });
         self.parents[b] = a;
         if self.ranks[a] == self.ranks[b] {
-            self.log.push(Action::Rank { key: a, original_rank: self.ranks[a] });
+            self.log_action(Action::Rank { key: a, original_rank: self.ranks[a] });
             self.ranks[a] += 1;
         }
     }
@@ -88,7 +94,7 @@ impl<V> UnificationTable<V> {
     pub fn set_value(&mut self, a: UnificationKey, v: V) {
         let index = self.find(a);
         let original_value = self.values[index].replace(v);
-        self.log.push(Action::Value { key: index, original_value });
+        self.log_action(Action::Value { key: index, original_value });
     }
 
     pub fn unioned(&mut self, a: UnificationKey, b: UnificationKey) -> bool {
@@ -106,7 +112,7 @@ impl<V> UnificationTable<V> {
             // a = parent.parent
             let a = self.parents[parent];
             // root.parent = parent.parent
-            self.log.push(Action::Parent { key: root, original_parent: self.parents[root] });
+            self.log_action(Action::Parent { key: root, original_parent: self.parents[root] });
             self.parents[root] = a;
             root = parent;
             // parent = root.parent