diff --git a/stepper.py b/stepper.py
index e74f166..6d63e02 100644
--- a/stepper.py
+++ b/stepper.py
@@ -41,6 +41,12 @@ def step(insns, terminator, blocks, stack_frames, ssa_env, global_env, memory,
         # TODO
         print('{} {}, {}'
               .format(bop, left_v, right_v))
+    elif isinstance(next_insn, ll.Alloca):
+        TODO('Alloca')
+    elif isinstance(next_insn, ll.Load):
+        TODO('Load')
+    elif isinstance(next_insn, ll.Store):
+        TODO('Store')
     elif isinstance(next_insn, ll.Icmp):
         cnd = next_insn.cnd
         left = next_insn.left
@@ -96,6 +102,8 @@ def step(insns, terminator, blocks, stack_frames, ssa_env, global_env, memory,
         # TODO
         print('bitcast {} {} to {}'
               .format(ll.ty2s(from_ty), oper_v, ll.ty2s(to_ty)))
+    elif isinstance(next_insn, ll.Gep):
+        TODO('Gep')
     elif isinstance(next_insn, ll.Zext):
         oper = next_insn.oper
         from_ty = next_insn.from_ty
@@ -126,6 +134,9 @@ def step(insns, terminator, blocks, stack_frames, ssa_env, global_env, memory,
         if ssa_target in ssa_env:
             err('Cannot assign to variable twice: {}'
                 .format(ssa_target))
+        elif res is None:
+            err('Cannot assign empty value to %{}'
+                .format(ssa_target))
         else:
             # TODO
             print('%{} <- {}'