diff --git a/nac3core/src/lib.rs b/nac3core/src/lib.rs
index 69faf0bede..53d5d36efe 100644
--- a/nac3core/src/lib.rs
+++ b/nac3core/src/lib.rs
@@ -5,6 +5,7 @@ extern crate num_bigint;
 extern crate inkwell;
 extern crate rustpython_parser;
 
+pub mod typedef;
 use std::error::Error;
 use std::fmt;
 use std::path::Path;
diff --git a/nac3core/src/typedef.rs b/nac3core/src/typedef.rs
new file mode 100644
index 0000000000..bec61fd115
--- /dev/null
+++ b/nac3core/src/typedef.rs
@@ -0,0 +1,60 @@
+use std::collections::HashMap;
+use std::rc::Rc;
+
+#[derive(PartialEq, Eq, Copy, Clone, Hash, Debug)]
+pub struct PrimitiveId(pub(crate) usize);
+
+#[derive(PartialEq, Eq, Copy, Clone, Hash, Debug)]
+pub struct ClassId(pub(crate) usize);
+
+#[derive(PartialEq, Eq, Copy, Clone, Hash, Debug)]
+pub struct ParamId(pub(crate) usize);
+
+#[derive(PartialEq, Eq, Copy, Clone, Hash, Debug)]
+pub struct VariableId(pub(crate) usize);
+
+#[derive(PartialEq, Eq, Clone, Hash, Debug)]
+pub enum TypeEnum {
+    BotType,
+    SelfType,
+    PrimitiveType(PrimitiveId),
+    ClassType(ClassId),
+    VirtualClassType(ClassId),
+    ParametricType(ParamId, Vec<Rc<TypeEnum>>),
+    TypeVariable(VariableId),
+}
+
+pub type Type = Rc<TypeEnum>;
+
+#[derive(Clone)]
+pub struct FnDef {
+    // we assume methods first argument to be SelfType,
+    // so the first argument is not contained here
+    pub args: Vec<Type>,
+    pub result: Option<Type>,
+}
+
+#[derive(Clone)]
+pub struct TypeDef<'a> {
+    pub name: &'a str,
+    pub fields: HashMap<&'a str, Type>,
+    pub methods: HashMap<&'a str, FnDef>,
+}
+
+#[derive(Clone)]
+pub struct ClassDef<'a> {
+    pub base: TypeDef<'a>,
+    pub parents: Vec<ClassId>,
+}
+
+#[derive(Clone)]
+pub struct ParametricDef<'a> {
+    pub base: TypeDef<'a>,
+    pub params: Vec<VariableId>,
+}
+
+#[derive(Clone)]
+pub struct VarDef<'a> {
+    pub name: &'a str,
+    pub bound: Vec<Type>,
+}