diff --git a/run_tests.sh.in b/run_tests.sh.in
index d9a1be9..3868185 100755
--- a/run_tests.sh.in
+++ b/run_tests.sh.in
@@ -8,4 +8,4 @@ for test in $TESTS; do
     if [ $? -ne 0 ] ; then
         exit $ret
     fi
-done
+done | tee | grep "Tests"
diff --git a/src/builtins.c b/src/builtins.c
index 2be67ad..ac29223 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -154,41 +154,6 @@ LISP_FUNC_0(ucl_builtin_now_millis_mono, state) {
     return NULL;
 }
 
-static void ucl_print_obj(struct ucl_object *obj) {
-    switch (obj->type) {
-        case UCL_TYPE_SYMBOL:
-            printf("%s", obj->symbol);
-            break;
-        case UCL_TYPE_INT:
-            printf("%d", obj->integer);
-            break;
-        case UCL_TYPE_STRING:
-            printf("\"%s\"", obj->string);
-            break;
-        case UCL_TYPE_ERROR:
-            printf("(error \"%s\")", obj->error);
-            break;
-        case UCL_TYPE_BUILTIN:
-            printf("<builtin %p>", obj->builtin);
-            break;
-        case UCL_TYPE_CELL: {
-            int first = true;
-            printf("%s", "(");
-            FOREACH_LIST(obj, iter, item) {
-                if (!first) {
-                    printf(" ");
-                }
-                ucl_print_obj(item);
-                first = false;
-            }
-            printf("%s",  ")");
-            break;
-        }
-        case UCL_TYPE_COUNT:
-            assert(0);
-    }
-}
-
 LISP_FUNC_1(ucl_builtin_print, state, arg0) {
     ucl_print_obj(arg0);
 
diff --git a/src/evaluate.c b/src/evaluate.c
index 9d6f358..c0fbd0c 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -19,17 +19,28 @@ struct ucl_object *ucl_evaluate_builtin_form(struct ucl_state *state, struct ucl
     };
 
     struct ucl_object *fun = ucl_car(evaluated_list);
-    struct ucl_object *args = ucl_cdr(evaluated_list);
     struct ucl_object *result = NULL;
 
-    assert(fun->type == UCL_TYPE_BUILTIN);
     if (fun->type == UCL_TYPE_BUILTIN) {
+        struct ucl_object *args = ucl_cdr(evaluated_list);
         result = fun->builtin(state, args);
+    } else if (fun->type == UCL_TYPE_CELL) {
+        struct ucl_state *fun_state = ucl_state_create_child(state);
+        struct ucl_object *fun_arg_syms = ucl_car(fun);
+        struct ucl_object *fun_forms = ucl_cdr(fun);
+        int i = 0;
+        FOREACH_LIST(fun_arg_syms, iter, sym) {
+            ucl_state_put(fun_state, sym->symbol, ucl_list_nth(evaluated_list, i + 1));
+            i++;
+        }
+        result = ucl_progn(fun_state, fun_forms);
+    } else {
+        assert(0);
     }
 
     // TODO: cleanup
 
-    return result;
+    return (result == NULL) ? ucl_nil_create() : result;
 }
 
 struct ucl_object *ucl_evaluate_special_form(struct ucl_state *state, struct ucl_object *list) {
@@ -45,7 +56,18 @@ struct ucl_object *ucl_evaluate_special_form(struct ucl_state *state, struct ucl
     return result;
 }
 
+struct ucl_object *ucl_evaluate_lisp_form(struct ucl_state *state, struct ucl_object *list) {
+    // TODO: Recursively eval args
+    const char *fun_sym = ucl_car(list)->symbol;
 
+    struct ucl_object *fun = ucl_state_get(state, ucl_car(list)->symbol);
+    struct ucl_object *args = ucl_cdr(list);
+    struct ucl_object *result = NULL;
+
+    result = fun->special(state, args);
+
+    return result;
+}
 
 struct ucl_object *ucl_evaluate_list(struct ucl_state *state, struct ucl_object *list) {
     if (list->cell.car == NULL) {
@@ -61,7 +83,7 @@ struct ucl_object *ucl_evaluate_list(struct ucl_state *state, struct ucl_object
 
     if (fun->type == UCL_TYPE_SPECIAL) {
         return ucl_evaluate_special_form(state, list);
-    } else if (fun->type == UCL_TYPE_BUILTIN) {
+    } else if (fun->type == UCL_TYPE_BUILTIN || fun->type == UCL_TYPE_CELL) {
         return ucl_evaluate_builtin_form(state, list);
     } else {
         assert(0);
diff --git a/src/main.c b/src/main.c
index 8e76b9d..66c7bde 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,5 +1,5 @@
-#include <assert.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 #include "uclisp.h"
 
@@ -15,7 +15,7 @@ int main(int argc, const char **argv) {
 
     ucl_state_put(state, "let", ucl_special_create(ucl_special_let));
     ucl_state_put(state, "if", ucl_special_create(ucl_special_if));
-
+    ucl_state_put(state, "defun", ucl_special_create(ucl_special_defun));
 
     ucl_state_put(state, "print", ucl_builtin_create(ucl_builtin_print));
     ucl_state_put(state, "list", ucl_builtin_create(ucl_builtin_list));
@@ -35,13 +35,32 @@ int main(int argc, const char **argv) {
     ucl_state_put(state, "int-p", ucl_builtin_create(ucl_builtin_int_p));
     ucl_state_put(state, "list-p", ucl_builtin_create(ucl_builtin_list_p));
 
-    struct ucl_object *sexp = ucl_parse(argv[1]);
-    struct ucl_object *result = ucl_evaluate(state, ucl_car(sexp));
+    if (argc < 2) {
+        while (1) {
+            printf("> ");
+            char *line = NULL;
+            size_t len = 0;
+            ssize_t lineSize = 0;
+            lineSize = getline(&line, &len, stdin);
 
-    if (result->type == UCL_TYPE_ERROR) {
-        printf("%s", result->error);
-        return -1;
+            struct ucl_object *sexp = ucl_parse(line);
+            struct ucl_object *result = ucl_evaluate(state, ucl_car(sexp));
+            ucl_print_obj(result);
+            printf("\n");
+
+            free(line);
+        }
+    } else {
+        struct ucl_object *sexp = ucl_parse(argv[1]);
+        struct ucl_object *result = ucl_evaluate(state, ucl_car(sexp));
+
+        if (result->type == UCL_TYPE_ERROR) {
+            printf("%s", result->error);
+            return -1;
+        }
+
+        return 0;
     }
-
-    return 0;
 }
+
+// '(let (()) (defun foo (a b) (+ a b)) (foo 1 2))'
diff --git a/src/special.c b/src/special.c
index 531e31d..1c5c9c7 100644
--- a/src/special.c
+++ b/src/special.c
@@ -27,15 +27,7 @@ struct ucl_object *ucl_special_let(struct ucl_state *state, struct ucl_object *a
         ucl_state_put(let_state, sym->symbol, value);
     }
 
-    struct ucl_object *result = NULL;
-    FOREACH_LIST(expressions, iter, item) {
-        result = ucl_evaluate(let_state, item);
-        if (result->type == UCL_TYPE_ERROR) {
-            return result;
-        }
-    }
-
-
+    struct ucl_object *result = ucl_progn(state, expressions);
     ucl_state_delete(let_state);
     return result;
 }
diff --git a/src/utility.c b/src/utility.c
index eba225b..93bf12f 100644
--- a/src/utility.c
+++ b/src/utility.c
@@ -4,8 +4,10 @@
 #include "utility.h"
 
 #include <stddef.h>
+#include <assert.h>
 #include <stdbool.h>
 #include <string.h>
+#include <stdio.h>
 
 struct ucl_object *ucl_car(struct ucl_object *list) {
     UCL_COND_OR_RET_ERROR(
@@ -117,3 +119,50 @@ struct ucl_object *ucl_list_append(struct ucl_object *list, struct ucl_object *o
 
     return list;
 }
+
+void ucl_print_obj(struct ucl_object *obj) {
+    switch (obj->type) {
+        case UCL_TYPE_SYMBOL:
+            printf("%s", obj->symbol);
+            break;
+        case UCL_TYPE_INT:
+            printf("%d", obj->integer);
+            break;
+        case UCL_TYPE_STRING:
+            printf("\"%s\"", obj->string);
+            break;
+        case UCL_TYPE_ERROR:
+            printf("(error \"%s\")", obj->error);
+            break;
+        case UCL_TYPE_BUILTIN:
+            printf("<builtin %p>", obj->builtin);
+            break;
+        case UCL_TYPE_CELL: {
+            int first = true;
+            printf("%s", "(");
+            FOREACH_LIST(obj, iter, item) {
+                if (!first) {
+                    printf(" ");
+                }
+                ucl_print_obj(item);
+                first = false;
+            }
+            printf("%s",  ")");
+            break;
+        }
+        case UCL_TYPE_COUNT:
+            assert(0);
+    }
+}
+
+struct ucl_object *ucl_progn(struct ucl_state *state, struct ucl_object *forms) {
+    struct ucl_object *result = NULL;
+    FOREACH_LIST(forms, iter, form) {
+        result = ucl_evaluate(state, form);
+        if (result->type == UCL_TYPE_ERROR) {
+            return result;
+        }
+    }
+
+    return (result == NULL) ? ucl_nil_create() : result;
+}
diff --git a/src/utility.h b/src/utility.h
index 3a06f91..11706f3 100644
--- a/src/utility.h
+++ b/src/utility.h
@@ -18,6 +18,9 @@ struct ucl_object* ucl_list_nth(struct ucl_object *list, int n);
 struct ucl_object* ucl_list_append(struct ucl_object *list, struct ucl_object *obj);
 struct ucl_object* ucl_tuple_create(struct ucl_object *obj0, struct ucl_object *obj1);
 
+struct ucl_object *ucl_progn(struct ucl_state *state, struct ucl_object *forms);
+
+void ucl_print_obj(struct ucl_object *obj);
 
 #define UCL_RET_IF_ERROR(obj)                   \
     do {                                        \