diff --git a/schala-lang/language/src/reduced_ir/mod.rs b/schala-lang/language/src/reduced_ir/mod.rs
index 0a84cb6..c4af742 100644
--- a/schala-lang/language/src/reduced_ir/mod.rs
+++ b/schala-lang/language/src/reduced_ir/mod.rs
@@ -271,10 +271,10 @@ pub enum Expression {
 
 #[derive(Debug)]
 pub struct FunctionDefinition {
-    body: Vec<Statement>
+    pub body: Vec<Statement>
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum Function {
     Builtin(Builtin),
     UserDefined(DefId)
diff --git a/schala-lang/language/src/tree_walk_eval/mod.rs b/schala-lang/language/src/tree_walk_eval/mod.rs
index 189db57..8edb576 100644
--- a/schala-lang/language/src/tree_walk_eval/mod.rs
+++ b/schala-lang/language/src/tree_walk_eval/mod.rs
@@ -1,6 +1,7 @@
 use crate::reduced_ir::{ReducedIR, Expression, Lookup, Function, FunctionDefinition, Statement, Literal};
 use crate::symbol_table::{DefId};
 use crate::util::ScopeStack;
+use crate::builtin::Builtin;
 
 use std::fmt::Write;
 use std::convert::From;
@@ -101,7 +102,7 @@ impl RuntimeValue {
 enum Primitive {
     Tuple(Vec<Primitive>),
     Literal(Literal),
-    Callable(DefId),
+    Callable(Function),
     Unimplemented,
     /*
     PrimObject {
@@ -117,7 +118,7 @@ impl Primitive {
         match self {
             Primitive::Tuple(items) => Expression::Tuple(items.iter().map(|item| item.to_expr()).collect()),
             Primitive::Literal(lit) => Expression::Literal(lit.clone()),
-            Primitive::Callable(defid) => Expression::Callable(Function::UserDefined(defid.clone())),
+            Primitive::Callable(function) => Expression::Callable(function.clone()),
             Primitive::Unimplemented => Expression::Unimplemented,
         }
     }
@@ -177,12 +178,10 @@ impl<'a> State<'a> {
           Expression::Lookup { ref id, kind } => {
               let mem = id.into();
               match kind {
-                  Lookup::Function => {
-                      if self.environments.lookup(&mem).is_some() {
-                          Primitive::Callable(id.clone())
-                      } else {
-                          return Err(format!("Function not found for id: {}", id));
-                      }
+                  Lookup::Function => match self.environments.lookup(&mem) {
+                      //TODO is this right? not sure
+                      Some(RuntimeValue::Primitive(prim)) => prim.clone(),
+                      _ => return Err(format!("Function not found for id: {}", id)),
                   },
                   kind @ Lookup::LocalVar | kind @ Lookup::GlobalVar | kind @ Lookup::Param => {
                       match self.environments.lookup(&mem) {
@@ -205,7 +204,28 @@ impl<'a> State<'a> {
   }
 
   fn call_expression(&mut self, f: Expression, args: Vec<Expression>) -> EvalResult<Primitive> {
-      Err("Call expression not implemented".to_string().into())
+      let func = match self.expression(f)? {
+          Primitive::Callable(func) => func,
+          other => return Err(format!("Trying to call non-function value: {:?}", other)),
+      };
+      match func {
+          Function::Builtin(builtin) => self.apply_builtin(builtin, args),
+          Function::UserDefined(def_id) => self.apply_function(def_id, args),
+      }
+  }
+
+  fn apply_builtin(&mut self, builtin: Builtin, args: Vec<Expression>) -> EvalResult<Primitive> {
+      return Err("unimplemented apply-builtin".to_string());
+  }
+
+  fn apply_function(&mut self, def_id: DefId, args: Vec<Expression>) -> EvalResult<Primitive> {
+      let mem = (&def_id).into();
+      Ok(match self.environments.lookup(&mem) {
+          Some(RuntimeValue::Function(FunctionDefinition { body })) => {
+              return Err("unimplemented apply-function".to_string());
+          },
+          e => return Err(format!("Error looking up function with id {}: {:?}", def_id, e)),
+      })
   }
 }