diff --git a/nac3core/Cargo.toml b/nac3core/Cargo.toml
index 6b15049d4..50ba54edb 100644
--- a/nac3core/Cargo.toml
+++ b/nac3core/Cargo.toml
@@ -11,8 +11,8 @@ inkwell = { git = "https://github.com/TheDan64/inkwell", branch = "master", feat
 rustpython-parser = { git = "https://github.com/RustPython/RustPython", branch = "master" }
 indoc = "1.0"
 ena = "0.14"
+itertools = "0.10.1"
 
 [dev-dependencies]
 test-case = "1.2.0"
-itertools = "0.10.1"
 
diff --git a/nac3core/src/lib.rs b/nac3core/src/lib.rs
index fceaaeea8..74440eefe 100644
--- a/nac3core/src/lib.rs
+++ b/nac3core/src/lib.rs
@@ -6,6 +6,7 @@ extern crate inkwell;
 extern crate rustpython_parser;
 extern crate indoc;
 extern crate ena;
+extern crate itertools;
 
 mod typecheck;
 
diff --git a/nac3core/src/typecheck/mod.rs b/nac3core/src/typecheck/mod.rs
index bb470cd01..cfab64c16 100644
--- a/nac3core/src/typecheck/mod.rs
+++ b/nac3core/src/typecheck/mod.rs
@@ -4,3 +4,4 @@ mod magic_methods;
 pub mod symbol_resolver;
 mod test_typedef;
 pub mod typedef;
+pub mod type_inferencer;
diff --git a/nac3core/src/typecheck/symbol_resolver.rs b/nac3core/src/typecheck/symbol_resolver.rs
index a6eff4409..accb1aaee 100644
--- a/nac3core/src/typecheck/symbol_resolver.rs
+++ b/nac3core/src/typecheck/symbol_resolver.rs
@@ -16,8 +16,8 @@ pub enum SymbolValue<'a> {
 }
 
 pub trait SymbolResolver {
-    fn get_symbol_type(&self, str: &str) -> Option<SymbolType>;
-    fn get_symbol_value(&self, str: &str) -> Option<SymbolValue>;
-    fn get_symbol_location(&self, str: &str) -> Option<Location>;
+    fn get_symbol_type(&mut self, str: &str) -> Option<SymbolType>;
+    fn get_symbol_value(&mut self, str: &str) -> Option<SymbolValue>;
+    fn get_symbol_location(&mut self, str: &str) -> Option<Location>;
     // handle function call etc.
 }
diff --git a/nac3core/src/typecheck/type_inferencer.rs b/nac3core/src/typecheck/type_inferencer.rs
new file mode 100644
index 000000000..3ccc3016f
--- /dev/null
+++ b/nac3core/src/typecheck/type_inferencer.rs
@@ -0,0 +1,227 @@
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::convert::TryInto;
+use std::iter::once;
+use std::rc::Rc;
+
+use super::magic_methods::*;
+use super::symbol_resolver::{SymbolResolver, SymbolType};
+use super::typedef::{Call, Type, TypeEnum, Unifier};
+use itertools::izip;
+use rustpython_parser::ast::{self, fold::Fold};
+
+pub struct PrimitiveStore {
+    int32: Type,
+    int64: Type,
+    float: Type,
+    bool: Type,
+    none: Type,
+}
+
+pub struct Inferencer<'a> {
+    resolver: &'a mut Box<dyn SymbolResolver>,
+    unifier: &'a mut Unifier,
+    variable_mapping: &'a mut HashMap<String, Type>,
+    calls: &'a mut Vec<Rc<Call>>,
+    primitives: &'a PrimitiveStore,
+}
+
+impl<'a> Fold<()> for Inferencer<'a> {
+    type TargetU = Option<Type>;
+    type Error = String;
+
+    fn map_user(&mut self, _: ()) -> Result<Self::TargetU, Self::Error> {
+        Ok(None)
+    }
+}
+
+type InferenceResult = Result<Type, String>;
+
+impl<'a> Inferencer<'a> {
+    fn build_method_call(
+        &mut self,
+        method: String,
+        obj: Type,
+        params: Vec<Type>,
+        ret: Type,
+    ) -> InferenceResult {
+        let call = Rc::new(Call {
+            posargs: params,
+            kwargs: HashMap::new(),
+            ret,
+            fun: RefCell::new(None),
+        });
+        self.calls.push(call.clone());
+        let call = self.unifier.add_ty(TypeEnum::TCall { calls: vec![call] });
+        let fields = once((method, call)).collect();
+        let record = self.unifier.add_ty(TypeEnum::TRecord { fields });
+        self.unifier.unify(obj, record)?;
+        Ok(ret)
+    }
+
+    fn infer_identifier(&mut self, id: &str) -> InferenceResult {
+        if let Some(ty) = self.variable_mapping.get(id) {
+            Ok(*ty)
+        } else {
+            match self.resolver.get_symbol_type(id) {
+                Some(SymbolType::TypeName(_)) => {
+                    Err("Expected expression instead of type".to_string())
+                }
+                Some(SymbolType::Identifier(ty)) => Ok(ty),
+                None => {
+                    let ty = self.unifier.get_fresh_var().0;
+                    self.variable_mapping.insert(id.to_string(), ty);
+                    Ok(ty)
+                }
+            }
+        }
+    }
+
+    fn infer_constant(&mut self, constant: &ast::Constant) -> InferenceResult {
+        match constant {
+            ast::Constant::Bool(_) => Ok(self.primitives.bool),
+            ast::Constant::Int(val) => {
+                let int32: Result<i32, _> = val.try_into();
+                // int64 would be handled separately in functions
+                if int32.is_ok() {
+                    Ok(self.primitives.int64)
+                } else {
+                    Err("Integer out of bound".into())
+                }
+            }
+            ast::Constant::Float(_) => Ok(self.primitives.float),
+            ast::Constant::Tuple(vals) => {
+                let ty: Result<Vec<_>, _> = vals.iter().map(|x| self.infer_constant(x)).collect();
+                Ok(self.unifier.add_ty(TypeEnum::TTuple { ty: ty? }))
+            }
+            _ => Err("not supported".into()),
+        }
+    }
+
+    fn infer_list(&mut self, elts: &[ast::Expr<Option<Type>>]) -> InferenceResult {
+        let (ty, _) = self.unifier.get_fresh_var();
+        for t in elts.iter() {
+            self.unifier.unify(ty, t.custom.unwrap())?;
+        }
+        Ok(ty)
+    }
+
+    fn infer_tuple(&mut self, elts: &[ast::Expr<Option<Type>>]) -> InferenceResult {
+        let ty = elts.iter().map(|x| x.custom.unwrap()).collect();
+        Ok(self.unifier.add_ty(TypeEnum::TTuple { ty }))
+    }
+
+    fn infer_attribute(&mut self, value: &ast::Expr<Option<Type>>, attr: &str) -> InferenceResult {
+        let (attr_ty, _) = self.unifier.get_fresh_var();
+        let fields = once((attr.to_string(), attr_ty)).collect();
+        let parent = self.unifier.add_ty(TypeEnum::TRecord { fields });
+        self.unifier.unify(value.custom.unwrap(), parent)?;
+        Ok(attr_ty)
+    }
+
+    fn infer_bool_ops(&mut self, values: &[ast::Expr<Option<Type>>]) -> InferenceResult {
+        let b = self.primitives.bool;
+        for v in values {
+            self.unifier.unify(v.custom.unwrap(), b)?;
+        }
+        Ok(b)
+    }
+
+    fn infer_bin_ops(
+        &mut self,
+        left: &ast::Expr<Option<Type>>,
+        op: &ast::Operator,
+        right: &ast::Expr<Option<Type>>,
+    ) -> InferenceResult {
+        let method = binop_name(op);
+        let ret = self.unifier.get_fresh_var().0;
+        self.build_method_call(
+            method.to_string(),
+            left.custom.unwrap(),
+            vec![right.custom.unwrap()],
+            ret,
+        )
+    }
+
+    fn infer_unary_ops(
+        &mut self,
+        op: &ast::Unaryop,
+        operand: &ast::Expr<Option<Type>>,
+    ) -> InferenceResult {
+        let method = unaryop_name(op);
+        let ret = self.unifier.get_fresh_var().0;
+        self.build_method_call(method.to_string(), operand.custom.unwrap(), vec![], ret)
+    }
+
+    fn infer_compare(
+        &mut self,
+        left: &ast::Expr<Option<Type>>,
+        ops: &[ast::Cmpop],
+        comparators: &[ast::Expr<Option<Type>>],
+    ) -> InferenceResult {
+        let boolean = self.primitives.bool;
+        for (a, b, c) in izip!(once(left).chain(comparators), comparators, ops) {
+            let method = comparison_name(c)
+                .ok_or_else(|| "unsupported comparator".to_string())?
+                .to_string();
+            self.build_method_call(method, a.custom.unwrap(), vec![b.custom.unwrap()], boolean)?;
+        }
+        Ok(boolean)
+    }
+
+    fn infer_subscript(
+        &mut self,
+        value: &ast::Expr<Option<Type>>,
+        slice: &ast::Expr<Option<Type>>,
+    ) -> InferenceResult {
+        let ty = self.unifier.get_fresh_var().0;
+        match &slice.node {
+            ast::ExprKind::Slice { lower, upper, step } => {
+                for v in [lower.as_ref(), upper.as_ref(), step.as_ref()]
+                    .iter()
+                    .flatten()
+                {
+                    self.unifier
+                        .unify(self.primitives.int32, v.custom.unwrap())?;
+                }
+                let list = self.unifier.add_ty(TypeEnum::TList { ty });
+                self.unifier.unify(value.custom.unwrap(), list)?;
+                Ok(list)
+            }
+            ast::ExprKind::Constant {
+                value: ast::Constant::Int(val),
+                ..
+            } => {
+                // the index is a constant, so value can be a sequence (either list/tuple)
+                let ind: i32 = val
+                    .try_into()
+                    .map_err(|_| "Index must be int32".to_string())?;
+                let map = once((ind, ty)).collect();
+                let seq = self.unifier.add_ty(TypeEnum::TSeq { map });
+                self.unifier.unify(value.custom.unwrap(), seq)?;
+                Ok(ty)
+            }
+            _ => {
+                // the index is not a constant, so value can only be a list
+                self.unifier
+                    .unify(slice.custom.unwrap(), self.primitives.int32)?;
+                let list = self.unifier.add_ty(TypeEnum::TList { ty });
+                self.unifier.unify(value.custom.unwrap(), list)?;
+                Ok(ty)
+            }
+        }
+    }
+
+    fn infer_if_expr(
+        &mut self,
+        test: &ast::Expr<Option<Type>>,
+        body: ast::Expr<Option<Type>>,
+        orelse: ast::Expr<Option<Type>>,
+    ) -> InferenceResult {
+        self.unifier
+            .unify(test.custom.unwrap(), self.primitives.bool)?;
+        self.unifier
+            .unify(body.custom.unwrap(), orelse.custom.unwrap())?;
+        Ok(body.custom.unwrap())
+    }
+}
diff --git a/nac3core/src/typecheck/typedef.rs b/nac3core/src/typecheck/typedef.rs
index 9c20f9182..d2da32ea3 100644
--- a/nac3core/src/typecheck/typedef.rs
+++ b/nac3core/src/typecheck/typedef.rs
@@ -52,24 +52,24 @@ type VarMap = Mapping<u32>;
 
 #[derive(Clone)]
 pub struct Call {
-    posargs: Vec<Type>,
-    kwargs: HashMap<String, Type>,
-    ret: Type,
-    fun: RefCell<Option<Type>>,
+    pub posargs: Vec<Type>,
+    pub kwargs: HashMap<String, Type>,
+    pub ret: Type,
+    pub fun: RefCell<Option<Type>>,
 }
 
 #[derive(Clone)]
 pub struct FuncArg {
-    name: String,
-    ty: Type,
-    is_optional: bool,
+    pub name: String,
+    pub ty: Type,
+    pub is_optional: bool,
 }
 
 #[derive(Clone)]
 pub struct FunSignature {
-    args: Vec<FuncArg>,
-    ret: Type,
-    params: VarMap,
+    pub args: Vec<FuncArg>,
+    pub ret: Type,
+    pub params: VarMap,
 }
 
 // We use a lot of `Rc`/`RefCell`s here as we want to simplify our code.