diff --git a/nac3core/src/typecheck/context/inference_context.rs b/nac3core/src/typecheck/context/inference_context.rs
index d1c76a36..93b97869 100644
--- a/nac3core/src/typecheck/context/inference_context.rs
+++ b/nac3core/src/typecheck/context/inference_context.rs
@@ -22,7 +22,7 @@ pub struct InferenceContext<'a> {
     /// File ID
     file: FileID,
 
-    /// identifier to (type, readable) mapping.
+    /// identifier to (type, readable, location) mapping.
     /// an identifier might be defined earlier but has no value (for some code path), thus not
     /// readable.
     sym_table: HashMap<&'a str, (Type, bool, Location)>,
diff --git a/nac3core/src/typecheck/expression_inference.rs b/nac3core/src/typecheck/expression_inference.rs
new file mode 100644
index 00000000..a7303e9f
--- /dev/null
+++ b/nac3core/src/typecheck/expression_inference.rs
@@ -0,0 +1,252 @@
+use std::convert::TryInto;
+
+use crate::typecheck::context::InferenceContext;
+use crate::typecheck::typedef::{Type, TypeEnum};
+use crate::typecheck::primitives;
+use rustpython_parser::ast;
+
+pub struct ExpressionTypeInferencer<'a> {
+    ctx: InferenceContext<'a>  
+}
+
+impl<'a> ExpressionTypeInferencer<'a>{ // NOTE: add location here in the function parameter for better error message?
+    
+    fn infer_constant_val(&mut self, constant: &ast::Constant) -> Result<Option<Type>, String> {
+        match constant {
+            ast::Constant::Bool(_) => 
+                Ok(Some(self.ctx.get_primitive(primitives::BOOL_TYPE))),
+            
+            ast::Constant::Int(val) => {
+                let int32: Result<i32, _> = val.try_into();
+                let int64: Result<i64, _> = val.try_into();
+                
+                if int32.is_ok() {
+                    Ok(Some(self.ctx.get_primitive(primitives::INT32_TYPE)))
+                } else if int64.is_ok() {
+                    Ok(Some(self.ctx.get_primitive(primitives::INT64_TYPE)))
+                } else {
+                    Err("Integer out of bound".into())
+                }
+            },
+    
+            ast::Constant::Float(_) => 
+                Ok(Some(self.ctx.get_primitive(primitives::FLOAT_TYPE))),
+
+            ast::Constant::Tuple(vals) => {
+                let result = vals
+                    .into_iter()
+                    .map(|x| self.infer_constant_val(x))
+                    .collect::<Vec<_>>();
+                
+                if result.iter().all(|x| x.is_ok()) {
+                    Ok(Some(TypeEnum::ParametricType(
+                        primitives::TUPLE_TYPE, 
+                        result
+                            .into_iter()
+                            .map(|x| x.unwrap().unwrap())
+                            .collect::<Vec<_>>(),
+                    ).into()))
+                } else {
+                    Err("Some elements in tuple cannot be typed".into())
+                }
+            }
+
+            _ => Err("not supported".into())
+        }
+    }
+
+
+    fn infer_list_val(&mut self, elts: &Vec<ast::Expr<Option<Type>>>) -> Result<Option<Type>, String> {
+        if elts.is_empty() {
+            Ok(Some(TypeEnum::ParametricType(primitives::LIST_TYPE, vec![TypeEnum::BotType.into()]).into()))
+        } else {
+            let types = elts
+                .into_iter()
+                .map(|x| &x.custom)
+                .collect::<Vec<_>>();
+            
+            if types.iter().all(|x| x.is_some()) {
+                let head = types.iter().next().unwrap(); // here unwrap alone should be fine after the previous check
+                if types.iter().all(|x| x.eq(head)) {
+                    Ok(Some(TypeEnum::ParametricType(primitives::LIST_TYPE, vec![(*head).clone().unwrap()]).into()))
+                } else {
+                    Err("inhomogeneous list is not allowed".into())
+                }
+            } else {
+                Err("list elements must have some type".into())
+            }
+
+        }
+    }
+}
+
+// REVIEW: field custom: from None to Option<Type> or just Option<Type> ?
+impl<'a> ast::fold::Fold<Option<Type>> for ExpressionTypeInferencer<'a> {
+    type TargetU = Option<Type>;
+    type Error = String;
+
+    fn map_user(&mut self, user: Option<Type>) -> Result<Self::TargetU, Self::Error> {
+        Ok(user)
+    }
+
+    fn fold_expr(&mut self, expr: ast::Expr<Option<Type>>) -> Result<ast::Expr<Self::TargetU>, Self::Error> {
+        let ast::Expr {location, custom: cus, node} = expr;
+        match node {
+            ast::ExprKind::Constant {value, kind} => 
+                Ok(ast::Expr {
+                    location, 
+                    custom: self.infer_constant_val(&value)?, 
+                    node: ast::ExprKind::Constant {value, kind}
+                }),
+            
+            ast::ExprKind::Name {id, ctx} =>
+                Ok(ast::Expr {
+                    location, 
+                    custom: Some(self.ctx.resolve(&*id)?),  // REVIEW: the conversion from String to &str is not sure
+                    node: ast::ExprKind::Name {id, ctx}
+                }), 
+
+            ast::ExprKind::List {elts, ctx} => {
+                let elts= elts
+                    .into_iter()
+                    .map(|x| self.fold_expr(x))
+                    .collect::<Result<Vec<ast::Expr<Option<Type>>>, _>>()?; // elements inside the vector should now have type info
+                
+                Ok(ast::Expr {
+                    location, 
+                    custom: self.infer_list_val(&elts)?,
+                    node: ast::ExprKind::List {elts, ctx}
+                })
+            }
+            
+            _ => 
+                Ok(ast::Expr {location, custom: cus, node: node})
+        }
+    }
+}
+
+mod test {
+
+    use crate::typecheck::{symbol_resolver::SymbolResolver, typedef::*, symbol_resolver::*, location::*};
+    use rustpython_parser::ast::{self, Expr, fold::Fold};
+    use super::*;
+    
+    fn new_ctx<'a>() -> ExpressionTypeInferencer<'a>{
+        struct S;
+
+        impl SymbolResolver for S {
+            fn get_symbol_location(&self, _str: &str) -> Option<Location> {
+                None
+            }
+        
+            fn get_symbol_type(&self, _str: &str) -> Option<SymbolType> {
+                None
+            }
+        
+            fn get_symbol_value(&self, _str: &str) -> Option<SymbolValue> {
+                None
+            }
+        }
+
+        ExpressionTypeInferencer {
+            ctx: InferenceContext::new(primitives::basic_ctx(), Box::new(S{}), FileID(3)),
+        }
+    }
+
+
+    #[test]
+    fn test_i64() {
+        let mut inferencer = new_ctx();
+
+        let location = ast::Location::new(0, 0);
+        let num: i64 = 99999999999;
+
+        let ast: Expr<Option<Type>> = Expr {
+            location: location,
+            custom: None,
+            node: ast::ExprKind::Constant {
+                value: ast::Constant::Int(num.into()),
+                kind: None,
+            }
+        };
+        
+        let new_ast = inferencer.fold_expr(ast).unwrap();
+
+        assert_eq!(
+            new_ast, 
+            Expr {
+                location: location,
+                custom: Some(inferencer.ctx.get_primitive(primitives::INT64_TYPE)),
+                node: ast::ExprKind::Constant {
+                    value: ast::Constant::Int(num.into()),
+                    kind: None,
+                }
+            }
+        );
+    }
+
+    #[test]
+    fn test_list() {
+        let mut inferencer = new_ctx();
+        let location = ast::Location::new(0, 0);
+
+        let ast: Expr<Option<Type>> = Expr {
+            location,
+            custom: None,
+            node: ast::ExprKind::List {
+                ctx: ast::ExprContext::Load,
+                elts: vec![
+                    Expr {
+                        location,
+                        custom: None,
+                        node: ast::ExprKind::Constant {
+                            value: ast::Constant::Int(1.into()),
+                            kind: None,
+                        },
+                    },
+
+                    Expr {
+                        location,
+                        custom: None,
+                        node: ast::ExprKind::Constant {
+                            value: ast::Constant::Int(2.into()),
+                            kind: None,
+                        },
+                    },
+                ],
+            }
+        };
+
+        let new_ast = inferencer.fold_expr(ast).unwrap();
+        assert_eq!(
+            new_ast,
+            Expr {
+                location,
+                custom: Some(TypeEnum::ParametricType(primitives::LIST_TYPE, vec![inferencer.ctx.get_primitive(primitives::INT32_TYPE).into()]).into()),
+                node: ast::ExprKind::List {
+                    ctx: ast::ExprContext::Load,
+                    elts: vec![
+                        Expr {
+                            location,
+                            custom: Some(inferencer.ctx.get_primitive(primitives::INT32_TYPE)),
+                            node: ast::ExprKind::Constant {
+                                value: ast::Constant::Int(1.into()),
+                                kind: None,
+                            },
+                        },
+    
+                        Expr {
+                            location,
+                            custom: Some(inferencer.ctx.get_primitive(primitives::INT32_TYPE)),
+                            node: ast::ExprKind::Constant {
+                                value: ast::Constant::Int(2.into()),
+                                kind: None,
+                            },
+                        },
+                    ],
+                }
+            }
+        );
+    }
+
+}
diff --git a/nac3core/src/typecheck/mod.rs b/nac3core/src/typecheck/mod.rs
index a3be5925..32eb09c6 100644
--- a/nac3core/src/typecheck/mod.rs
+++ b/nac3core/src/typecheck/mod.rs
@@ -5,3 +5,4 @@ pub mod magic_methods;
 pub mod primitives;
 pub mod symbol_resolver;
 pub mod typedef;
+pub mod expression_inference;