diff --git a/nac3core/src/expression.rs b/nac3core/src/expression.rs
new file mode 100644
index 00000000..2329d943
--- /dev/null
+++ b/nac3core/src/expression.rs
@@ -0,0 +1,66 @@
+use crate::inference::resolve_call;
+use crate::primitives::*;
+use crate::typedef::{GlobalContext, Type, Type::*};
+use rustpython_parser::ast::{Expression, ExpressionType};
+use std::collections::HashMap;
+use std::convert::TryFrom;
+use std::rc::Rc;
+
+type SymTable<'a> = HashMap<&'a str, Rc<Type>>;
+type ParserResult = Result<Rc<Type>, String>;
+
+pub fn parse_expr(ctx: &GlobalContext, sym_table: &SymTable, expr: &Expression) -> ParserResult {
+    Err("not supported".to_string())
+}
+
+fn parse_constant(
+    ctx: &GlobalContext,
+    sym_table: &SymTable,
+    value: &rustpython_parser::ast::Number,
+) -> ParserResult {
+    use rustpython_parser::ast::Number;
+    match value {
+        Number::Integer { value } => {
+            if i32::try_from(&value).is_ok() {
+                Ok(PrimitiveType(INT32_TYPE).into())
+            } else if i64::try_from(&value).is_ok() {
+                Ok(PrimitiveType(INT64_TYPE).into())
+            } else {
+                Err("integer out of range".to_string())
+            }
+        }
+        Number::Float { .. } => Ok(PrimitiveType(FLOAT_TYPE).into()),
+        _ => Err("not supported".to_string()),
+    }
+}
+
+fn parse_identifier(ctx: &GlobalContext, sym_table: &SymTable, name: &str) -> ParserResult {
+    match sym_table.get(name) {
+        Some(v) => Ok(v.clone()),
+        None => Err("unbounded variable".to_string()),
+    }
+}
+
+fn parse_list(
+    ctx: &GlobalContext,
+    sym_table: &SymTable,
+    elements: &[Expression],
+) -> ParserResult {
+    if elements.len() == 0 {
+        return Ok(ParametricType(LIST_TYPE, vec![BotType.into()]).into());
+    }
+
+    let mut types = elements
+        .iter()
+        .map(|v| parse_expr(&ctx, sym_table, v));
+
+    let head = types.next().unwrap()?;
+    for v in types {
+        if v? != head {
+            return Err("inhomogeneous list is not allowed".to_string());
+        }
+    }
+    Ok(ParametricType(LIST_TYPE, vec![head]).into())
+}
+
+
diff --git a/nac3core/src/lib.rs b/nac3core/src/lib.rs
index 761cc82e..785dfc07 100644
--- a/nac3core/src/lib.rs
+++ b/nac3core/src/lib.rs
@@ -5,6 +5,7 @@ extern crate rustpython_parser;
 pub mod inference;
 pub mod primitives;
 pub mod typedef;
+pub mod expression;
 
 use std::error::Error;
 use std::fmt;