diff --git a/src/cell.rs b/src/cell.rs
index fd8e6a6..366a884 100644
--- a/src/cell.rs
+++ b/src/cell.rs
@@ -20,6 +20,7 @@ use std::boxed::Box;
 
 
 // Container
+#[derive(Clone)]
 pub enum Ctr {
     Symbol(String),
     String(String),
@@ -32,6 +33,7 @@ pub enum Ctr {
 
 // Type of Container
 #[derive(PartialEq)]
+#[derive(Clone)]
 pub enum Type {
     Symbol,
     String,
@@ -46,6 +48,7 @@ pub enum Type {
  * Holds two Containers.
  * Basic building block for more complex data structures.
  */
+#[derive(Clone)]
 pub struct Cell {
     /* "Cell Address Register"
      *  Historical way of referring to the first value in a cell.
@@ -165,7 +168,7 @@ impl Cell {
      * short circuits on the first false returned.
      * also returns false on a non standard form list
      */
-    pub fn circuit<F: FnOnce(Ctr)-> bool>(&mut self, func: F) -> bool{
+    pub fn circuit<F: FnOnce(Ctr)-> bool>(&self, func: F) -> bool{
         if func(self.car) {
             match self.cdr {
                 Ctr::None => true,
@@ -213,4 +216,31 @@ impl Cell {
             _ => 1
         }
     }
+
+    /* iterates through a list.
+     * returns a COPY of the cell at the cooresponding index
+     * WARNING: DESTRUCTIVE?
+     */
+    pub fn index(&self, idx: usize) -> Ctr {
+        if idx > 0 {
+            match self.cdr {
+                Ctr::None => Ctr::None,
+                Ctr::Cell(c) => c.index(idx-1),
+                _ => {
+                    if idx == 1 {
+                        self.cdr
+                    } else {
+                        Ctr::None
+                    }
+                }
+            }
+        } else {
+            match self.car {
+                Ctr::None => Ctr::None,
+                _ => {
+                    self.cdr
+                }
+            }
+        }
+    }
 }
diff --git a/src/eval.rs b/src/eval.rs
new file mode 100644
index 0000000..3fc355a
--- /dev/null
+++ b/src/eval.rs
@@ -0,0 +1,34 @@
+/* relish: versatile lisp shell
+ * Copyright (C) 2021 Aidan Hahn
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+use std::boxed::Box;
+use crate::cell::{Cell};
+use crate::func::FTable;
+use crate::vars::VTable;
+
+/* iterates over a syntax tree
+ * returns a NEW LIST of values
+ * representing the simplest possible form of the input
+ */
+pub fn eval(
+    _ast: Box<Cell>,
+    _vars: Box<VTable>,
+    _funcs: Box<FTable>,
+    _sym_loose: bool
+) -> Result<Box<Cell>, String> {
+    Err("Unimplemented".to_string())
+}
diff --git a/src/func.rs b/src/func.rs
index 416da33..698e34a 100644
--- a/src/func.rs
+++ b/src/func.rs
@@ -16,14 +16,33 @@
  */
 
 use std::boxed::Box;
+use std::convert::TryInto;
 use std::collections::HashMap;
 use crate::cell::{Ctr, Cell, Type};
 use crate::vars::{VTable};
 use crate::eval::eval;
 
+pub type FTable = HashMap<String, Box<Function>>;
+
 // Standardized function signature for stdlib functions
-pub type Operation = fn(Box<Cell>, Box<VTable>, Box<FTable>) -> Box<Cell>;
-pub type FTable = HashMap<String, Function>;
+pub type InternalOperation = fn(Box<Cell>, Box<VTable>, Box<FTable>) -> Box<Cell>;
+pub struct ExternalOperation {
+    // Un-evaluated abstract syntax tree
+    // TODO: Intermediate evaluation to simplify branches with no argument in them
+    //       Simplified branches must not have side effects.
+    // TODO: Apply Memoization?
+    ast: Box<Cell>,
+    // list of argument string tokens
+    arg_syms: Vec<String>
+}
+
+/* A stored function may either be a pointer to a function
+ * or a syntax tree to eval with the arguments
+ */
+pub enum Operation {
+    Internal(InternalOperation),
+    External(ExternalOperation)
+}
 
 /* Function Args
  * If Lazy, is an integer denoting number of args
@@ -39,7 +58,6 @@ pub enum Args {
 pub struct Function {
     pub function: Operation,
     pub name: String,
-    pub times_called: u128,
     pub args: Args,
 
     // dont fail on undefined symbol (passed to eval)
@@ -53,9 +71,9 @@ impl Function {
     /* call
      * routine is called by eval when a function call is detected
      */
-    pub fn call_function (
-        &mut self,
-        args: Box<cell>,
+    pub fn call(
+        &self,
+        args: Box<Cell>,
         vars: Box<VTable>,
         funcs: Box<FTable>
     ) -> Result<Box<Cell>, String> {
@@ -66,33 +84,31 @@ impl Function {
                 Err(s) => return Err(
                     format!(
                         "error evaluating args to {}: {}",
-                        func.name,
+                        self.name,
                         s
                     )
                 )
             }
         }
 
-        let mut passes = false;
         match self.args {
             Args::Lazy(num) => {
                 if num < 0 {
-                    passes = true
                 }
 
-                if !(num == (args.len() - 1)) {
+                if !(num == (n_args.len() - 1)) {
                     return Err(format!("expected {} args in call to {}", num, self.name))
                 }
             },
 
             Args::Strict(arg_types) => {
                 let idx: usize = 0;
-                passes = args.circuit(|c: Ctr| {
+                let mut passes = args.circuit(|c: Ctr| {
                     if idx >= arg_types.len() {
                         return false;
                     }
 
-                    if let c = Ctr::None {
+                    if let Ctr::None = c {
                         return false;
                     }
 
@@ -104,7 +120,7 @@ impl Function {
                 });
 
                 if passes && idx < (arg_types.len() - 1) {
-                    Err(format!(
+                    return Err(format!(
                         "{} too little arguments in call to {}",
                         arg_types.len() - (idx + 1),
                         self.name
@@ -113,7 +129,7 @@ impl Function {
 
                 if !passes {
                     if idx < (arg_types.len() - 1) {
-                        Err(format!(
+                        return Err(format!(
                             "argument {} in call to {} is of wrong type (expected {})",
                             idx + 1,
                             self.name,
@@ -122,7 +138,7 @@ impl Function {
                     }
 
                     if idx == (arg_types.len() - 1) {
-                        Err(format!(
+                        return Err(format!(
                             "too many arguments in call to {}",
                             self.name
                         ));
@@ -131,24 +147,54 @@ impl Function {
             }
         }
 
-        self.times_called += 1;
-        return Ok((self.function)(args, vars, funcs));
+        match self.function {
+            Operation::Internal(f) => Ok((f)(n_args, vars, funcs)),
+            Operation::External(f) => {
+                // copy var table and add args
+                let temp = vars.clone();
+                for n in 0..f.arg_syms.len() {
+                    temp.insert(
+                        f.arg_syms[n],
+                        Box::new(n_args.index(n))
+                    );
+                }
+                eval(f.ast, temp, funcs, self.loose_syms)
+            }
+        }
     }
 }
 
-impl FTable {
-    pub fn declare(
-        &mut self,
-        f: Function
-    ) {
-        // memory leak here? where does Function go? maybe it should be boxed....
-        self.insert(f.name, f);
+pub fn declare(
+    ft: Box<FTable>,
+    f: Box<Function>
+) -> Option<String> {
+    if let Operation::External(fun) = f.function {
+        if let Args::Lazy(i) = f.args {
+            if fun.arg_syms.len() != i.try_into().unwrap() {
+                return Some(
+                    "external function must have lazy args equal to declared arg_syms length"
+                        .to_string()
+                );
+            }
+        } else {
+            return Some(
+                "external function must have lazy args"
+                    .to_string()
+            );
+        }
     }
 
-    pub fn get(
-        &mut self,
-        identifier: String
-    ) -> Result<Box<Cell>, String> {
-        self.get(identifier)
+    ft.insert(f.name, f);
+    None
+}
+
+pub fn get(
+    ft: Box<FTable>,
+    identifier: String
+) -> Option<Box<Function>> {
+    if let Some(f) = ft.get(&identifier) {
+        Some(*f)
+    } else {
+        None
     }
 }
diff --git a/src/lex.rs b/src/lex.rs
index dc8cbc2..8232e45 100644
--- a/src/lex.rs
+++ b/src/lex.rs
@@ -23,10 +23,6 @@ const UNMATCHED_LIST_DELIM: &str = "Unmatched list delimiter in input";
 
 /* takes a line of user input
  * returns an unsimplified tree of tokens.
- *
- * WARNING: lex and process ONLY SUPPORT ASCII CHARACTERS.
- * Unicode and other technology where one rune can take multiple indexes
- * can cause havoc if part of a rune matches a whitespace or other operator
  */
 pub fn lex(document: String) -> Result<Box<Cell>, String> {
     if !document.is_ascii() {
@@ -46,8 +42,6 @@ pub fn lex(document: String) -> Result<Box<Cell>, String> {
 /* The logic used in lex
  * Returns Ok(Box<Cell>) if lexing passes
  * Returns Err(String) if an error occurs
- *
- * WARNING: read docs for lex
  */
 fn process(document: String) -> Result<Box<Cell>, String> {
     let doc_len = document.len();
diff --git a/src/lib.rs b/src/lib.rs
index 7ee3609..5ca14df 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -19,10 +19,12 @@ mod cell;
 mod lex;
 mod func;
 mod eval;
+mod vars;
 
 pub mod ast {
     pub use crate::cell::{Cell, Ctr, cons, cell_as_string};
     pub use crate::lex::{lex};
     pub use crate::func::{Function, Operation, FTable};
+    pub use crate::vars::VTable;
     pub use crate::eval::{eval};
 }
diff --git a/src/vars.rs b/src/vars.rs
index e7c5f37..24c8f87 100644
--- a/src/vars.rs
+++ b/src/vars.rs
@@ -17,7 +17,7 @@
 
 use std::boxed::Box;
 use std::collections::HashMap;
-use crate::cell::{Ctr, Cell};
+use crate::cell::{Ctr};
 
 /* Mapping between a string token and a tree of Cells
  * The string token can be found in any Ctr::Symbol value
@@ -25,23 +25,25 @@ use crate::cell::{Ctr, Cell};
  * Considerations: should I use a structure of cells for this?
  * Current thoughts: if this was a language without proper data types, yes.
  */
-pub type VTable = HashMap<String, Cell>;
+pub type VTable = HashMap<String, Box<Ctr>>;
 
-impl VTable {
-    pub fn define(
-        &mut self,
-        identifier: String,
-        var_tree: Box<Cell>
-    ) {
-        if let Some(boxed_cell) = self.insert(identifier, var_tree) {
-            drop(boxed_cell);
-        }
-    }
-
-    pub fn get(
-        &self,
-        identifier: String
-    ) -> Option<Box<Cell>> {
-        self.get(identifier)
+pub fn define(
+    vt: Box<VTable>,
+    identifier: String,
+    var_tree: Box<Ctr>
+) {
+    if let Some(boxed_cell) = vt.insert(identifier, var_tree) {
+        drop(boxed_cell);
+    }
+}
+
+pub fn get(
+    vt: Box<VTable>,
+    identifier: String
+) -> Option<Box<Ctr>> {
+    if let Some(c) = vt.get(&identifier) {
+        Some(*c)
+    } else {
+        None
     }
 }