diff --git a/src/backend/c-lisp.py b/src/backend/c-lisp.py
index ba5c708..6b00556 100755
--- a/src/backend/c-lisp.py
+++ b/src/backend/c-lisp.py
@@ -2,6 +2,7 @@
 import json
 import sys
 from utils.random import random_label
+from utils.shape import verify_shape
 
 CLISP_PREFIX = "tmp_clisp"
 
@@ -87,10 +88,53 @@ def gen_function(self, func):
             parm_types.append(parm[1])
             self.symbol_types[parm[0]] = parm[1]
         self.function_types[name] = [ret_type, parm_types]
+
+        # If the function has a body, we need to codegen for it
+        if len(func) > 2:
+            # Set up a return label and a return variable, if needed
+            self.ret_ptr_sym, ret_label, ret_alloc_size_sym, ret_val_sym = [
+                random_label(CLISP_PREFIX, [extra])
+                for extra in ("ret_ptr", "ret_lbl", "ret_alloc", "ret_val")
+            ]
+            self.ret_jmp_instr = ["jmp", ret_label]
+            if ret_type != "void":
+                # Function returns something, so we have to maintain a return variable
+                ret_alloc_instrs = [
+                    # Allocate space for the return variable
+                    ["set", [ret_alloc_size_sym, "int"], ["const", 1]],
+                    [
+                        "set",
+                        [self.ret_ptr_sym, ["ptr", ret_type]],
+                        ["alloc", ret_alloc_size_sym],
+                    ],
+                ]
+                ret_label_instrs = [
+                    # Load the return variable and return it.
+                    # Control jumps here for function return.
+                    ["label", ret_label],
+                    ["set", [ret_val_sym, ret_type], ["load", self.ret_ptr_sym]],
+                    ["ret", ret_val_sym],
+                ]
+            else:
+                # No return value, so no need to maintain a return variable
+                ret_alloc_instrs = []
+                ret_label_instrs = [["label", ret_label], ["ret"]]
+
+            body_instrs = [
+                *ret_alloc_instrs,
+                *self.gen_compound_stmt(
+                    func[2:], new_scope=False
+                ),  # C-Lisp function body
+                *ret_label_instrs,
+            ]
+        else:
+            # This is a declaration without a body
+            body_instrs = []
+
         return [
             "define",
             func[1],
-            *self.gen_compound_stmt(func[2:], new_scope=False),
+            *body_instrs,
         ]
 
     def gen_stmt(self, stmt):
@@ -115,7 +159,7 @@ def gen_stmt(self, stmt):
             else:
                 return self.gen_expr(stmt)
         except Exception as e:
-            print(f"Error in statement: {stmt}")
+            print(f"Error in statement: {stmt}", file=sys.stderr)
             raise e
 
     def is_while_stmt(self, stmt):
@@ -219,7 +263,7 @@ def is_decl_stmt(self, stmt):
 
     def gen_decl_stmt(self, stmt):
         if not len(stmt) == 3:
-            raise CodegenError(f"bad declare statement: {stmt}")
+            raise CodegenError(f"Bad declare statement: {stmt}")
 
         name, typ = stmt[1], stmt[2]
         scoped_name = self.construct_scoped_name(name, self.scopes)
@@ -233,11 +277,14 @@ def is_ret_stmt(self, stmt):
 
     def gen_ret_stmt(self, stmt):
         if len(stmt) == 1:
-            return [["ret"]]
+            return [self.ret_jmp_instr]
         elif len(stmt) == 2:
             res_sym = random_label(CLISP_PREFIX)
-            instr_list = self.gen_expr(stmt[1], res_sym=res_sym)
-            instr_list.append(["ret", res_sym])
+            instr_list = [
+                *self.gen_expr(stmt[1], res_sym=res_sym),
+                ["store", self.ret_ptr_sym, res_sym],
+                self.ret_jmp_instr,
+            ]
             return instr_list
         else:
             raise CodegenError(
@@ -262,11 +309,11 @@ def is_set_expr(self, expr):
         return expr[0] == "set"
 
     def gen_set_expr(self, expr, res_sym):
+        if not verify_shape(expr, [str, str, None]):
+            raise CodegenError(f"Bad set expression: {expr}")
+
         name = expr[1]
         scoped_name = self.scoped_lookup(name)
-        if not scoped_name in self.symbol_types:
-            raise CodegenError(f"Cannot set undeclared variable: {name}")
-
         instr_list = self.gen_expr(expr[2], res_sym=res_sym)
         instr_list.append(
             ["set", [scoped_name, self.symbol_types[scoped_name]], ["id", res_sym]]
@@ -300,6 +347,8 @@ def gen_call_expr(self, expr, res_sym):
             arg_syms.append(arg_sym)
             instr_list += self.gen_expr(arg, res_sym=arg_sym)
         name = expr[1]
+        if name not in self.function_types:
+            raise CodegenError(f"Call to undeclared function: {name}")
         instr_list.append(
             ["set", [res_sym, self.function_types[name][0]], ["call", name, *arg_syms]]
         )
@@ -310,14 +359,11 @@ def is_var_expr(self, expr):
 
     def gen_var_expr(self, expr, res_sym):
         scoped_name = self.scoped_lookup(expr)
-        if scoped_name in self.symbol_types:
-            typ = self.symbol_types[scoped_name]
-            instr_list = [["set", [res_sym, typ], ["id", scoped_name]]]
-            if typ[0] == "ptr":
-                self.pointer_types[res_sym] = typ
-            return instr_list
-        else:
-            raise CodegenError(f"Reference to undeclared variable: {expr}")
+        typ = self.symbol_types[scoped_name]
+        instr_list = [["set", [res_sym, typ], ["id", scoped_name]]]
+        if typ[0] == "ptr":
+            self.pointer_types[res_sym] = typ
+        return instr_list
 
     def is_fixed_type_expr(self, expr):
         return expr[0] in self.fixed_op_types
@@ -327,10 +373,8 @@ def gen_fixed_type_expr(self, expr, res_sym):
         opcode = expr[0]
         typ, n_ops = self.fixed_op_types[opcode]
         if not (len(expr) == n_ops + 1):
-            raise CodegenError(f"`{opcode}` takes only 2 operands: {expr}")
-        in_syms = [
-            random_label(CLISP_PREFIX, [f"inp_{n}"]) for n in range(n_ops)
-        ]
+            raise CodegenError(f"`{opcode}` takes only {n_ops} operands: {expr}")
+        in_syms = [random_label(CLISP_PREFIX, [f"inp_{n}"]) for n in range(n_ops)]
         input_instrs = []
         for n in range(n_ops):
             input_instrs += [*self.gen_expr(expr[n + 1], in_syms[n])]
@@ -376,8 +420,7 @@ def gen_store_expr(self, expr, res_sym):
             raise CodegenError(f"Bad store expression: {expr}")
 
         val_sym, ptr_sym = [
-            random_label(CLISP_PREFIX, [extra])
-            for extra in ("val", "ptr")
+            random_label(CLISP_PREFIX, [extra]) for extra in ("val", "ptr")
         ]
         return [
             *self.gen_expr(expr[1], res_sym=ptr_sym),
diff --git a/src/backend/tests/c-lisp/errors/alloc-bad.out b/src/backend/tests/c-lisp/errors/alloc-bad.out
new file mode 100644
index 0000000..b9e99d8
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/alloc-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['set', 'arr', ['alloc', 3]]
+CodegenError: Bad alloc expression: ['alloc', 3]
diff --git a/src/backend/tests/c-lisp/errors/alloc-bad.sexp b/src/backend/tests/c-lisp/errors/alloc-bad.sexp
new file mode 100644
index 0000000..33adc4a
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/alloc-bad.sexp
@@ -0,0 +1,4 @@
+(c-lisp
+    (define ((main void))
+        (declare arr (ptr float))
+        (set arr (alloc 3))))
diff --git a/src/backend/tests/c-lisp/errors/bad-expression.out b/src/backend/tests/c-lisp/errors/bad-expression.out
new file mode 100644
index 0000000..07c8b50
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/bad-expression.out
@@ -0,0 +1,2 @@
+Error in statement: ['while', [True], ['call', 'print', 4]]
+CodegenError: Bad expression: [True]
diff --git a/src/backend/tests/c-lisp/errors/bad-expression.sexp b/src/backend/tests/c-lisp/errors/bad-expression.sexp
new file mode 100644
index 0000000..a0a6e04
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/bad-expression.sexp
@@ -0,0 +1,4 @@
+(c-lisp
+    (define ((main int))
+        (while (#t)
+            (call print 4))))
diff --git a/src/backend/tests/c-lisp/errors/declare-bad.out b/src/backend/tests/c-lisp/errors/declare-bad.out
new file mode 100644
index 0000000..c1aba82
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/declare-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['declare', 'a']
+CodegenError: Bad declare statement: ['declare', 'a']
diff --git a/src/backend/tests/c-lisp/errors/declare-bad.sexp b/src/backend/tests/c-lisp/errors/declare-bad.sexp
new file mode 100644
index 0000000..361879e
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/declare-bad.sexp
@@ -0,0 +1,4 @@
+(c-lisp
+    (define ((main void))
+        (declare a)
+        (call print a)))
diff --git a/src/backend/tests/c-lisp/errors/fixed-op-count-1.out b/src/backend/tests/c-lisp/errors/fixed-op-count-1.out
new file mode 100644
index 0000000..4cef219
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/fixed-op-count-1.out
@@ -0,0 +1,2 @@
+Error in statement: ['ret', ['not', True, False]]
+CodegenError: `not` takes only 1 operands: ['not', True, False]
diff --git a/src/backend/tests/c-lisp/errors/fixed-op-count-1.sexp b/src/backend/tests/c-lisp/errors/fixed-op-count-1.sexp
new file mode 100644
index 0000000..bc9e359
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/fixed-op-count-1.sexp
@@ -0,0 +1,3 @@
+(c-lisp
+    (define ((main bool))
+        (ret (not #t #f))))
diff --git a/src/backend/tests/c-lisp/errors/fixed-op-count-2.out b/src/backend/tests/c-lisp/errors/fixed-op-count-2.out
new file mode 100644
index 0000000..ee48f23
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/fixed-op-count-2.out
@@ -0,0 +1,2 @@
+Error in statement: ['ret', ['add', 3, 4, 5]]
+CodegenError: `add` takes only 2 operands: ['add', 3, 4, 5]
diff --git a/src/backend/tests/c-lisp/errors/fixed-op-count-2.sexp b/src/backend/tests/c-lisp/errors/fixed-op-count-2.sexp
new file mode 100644
index 0000000..41334c0
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/fixed-op-count-2.sexp
@@ -0,0 +1,3 @@
+(c-lisp
+    (define ((main int))
+        (ret (add 3 4 5))))
diff --git a/src/backend/tests/c-lisp/errors/fn-proto-bad.out b/src/backend/tests/c-lisp/errors/fn-proto-bad.out
new file mode 100644
index 0000000..7dabea7
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/fn-proto-bad.out
@@ -0,0 +1 @@
+CodegenError: Bad function prototype: ['main', 'int']
diff --git a/src/backend/tests/c-lisp/errors/fn-proto-bad.sexp b/src/backend/tests/c-lisp/errors/fn-proto-bad.sexp
new file mode 100644
index 0000000..e5019ad
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/fn-proto-bad.sexp
@@ -0,0 +1,3 @@
+(c-lisp
+    (define (main int)
+        (ret 0)))
diff --git a/src/backend/tests/c-lisp/errors/for-bad.out b/src/backend/tests/c-lisp/errors/for-bad.out
new file mode 100644
index 0000000..6824c13
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/for-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['for', [['lt', 'i', 10], ['set', ['add', 'i', 1]], ['call', 'print', 'i']]]
+CodegenError: Bad for statement: ['for', [['lt', 'i', 10], ['set', ['add', 'i', 1]], ['call', 'print', 'i']]]
diff --git a/src/backend/tests/c-lisp/errors/for-bad.sexp b/src/backend/tests/c-lisp/errors/for-bad.sexp
new file mode 100644
index 0000000..f1f1d34
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/for-bad.sexp
@@ -0,0 +1,6 @@
+(c-lisp
+    (define ((main void))
+        (declare i int)
+        (set i 0)
+        (for ((lt i 10) (set (add i 1))
+            (call print i)))))
diff --git a/src/backend/tests/c-lisp/errors/if-bad.out b/src/backend/tests/c-lisp/errors/if-bad.out
new file mode 100644
index 0000000..e2e33f0
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/if-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['if', True, ['call', 'print', 5], ['call', 'print', 4], ['call', 'print', 3]]
+CodegenError: Bad if statement: ['if', True, ['call', 'print', 5], ['call', 'print', 4], ['call', 'print', 3]]
diff --git a/src/backend/tests/c-lisp/errors/if-bad.sexp b/src/backend/tests/c-lisp/errors/if-bad.sexp
new file mode 100644
index 0000000..6021cd0
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/if-bad.sexp
@@ -0,0 +1,8 @@
+(c-lisp
+    (define ((print int) (n int)))
+
+    (define ((main void))
+        (if #t
+            (call print 5)
+            (call print 4)
+            (call print 3))))
diff --git a/src/backend/tests/c-lisp/errors/load-bad.out b/src/backend/tests/c-lisp/errors/load-bad.out
new file mode 100644
index 0000000..963ebb9
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/load-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['load', 'argv', 'a']
+CodegenError: Bad load expression: ['load', 'argv', 'a']
diff --git a/src/backend/tests/c-lisp/errors/load-bad.sexp b/src/backend/tests/c-lisp/errors/load-bad.sexp
new file mode 100644
index 0000000..76c394e
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/load-bad.sexp
@@ -0,0 +1,4 @@
+(c-lisp
+    (define ((main void) (argc int) (argv (ptr (ptr int))))
+        (declare a (ptr int))
+        (load argv a)))
diff --git a/src/backend/tests/c-lisp/errors/not-clisp.out b/src/backend/tests/c-lisp/errors/not-clisp.out
new file mode 100644
index 0000000..c5cd791
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/not-clisp.out
@@ -0,0 +1 @@
+CodegenError: Input not a C-Lisp program
diff --git a/src/backend/tests/c-lisp/errors/not-clisp.sexp b/src/backend/tests/c-lisp/errors/not-clisp.sexp
new file mode 100644
index 0000000..d38802c
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/not-clisp.sexp
@@ -0,0 +1,3 @@
+(brilisp
+    (define ((main int))
+        (ret 0)))
diff --git a/src/backend/tests/c-lisp/errors/not-function.out b/src/backend/tests/c-lisp/errors/not-function.out
new file mode 100644
index 0000000..e5695c3
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/not-function.out
@@ -0,0 +1 @@
+CodegenError: Not a function: ['declare', 'a', 'int']
diff --git a/src/backend/tests/c-lisp/errors/not-function.sexp b/src/backend/tests/c-lisp/errors/not-function.sexp
new file mode 100644
index 0000000..0c65d85
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/not-function.sexp
@@ -0,0 +1,4 @@
+(c-lisp
+    (declare a int)
+    (set a 5)
+    (return a))
diff --git a/src/backend/tests/c-lisp/errors/ptradd-bad.out b/src/backend/tests/c-lisp/errors/ptradd-bad.out
new file mode 100644
index 0000000..3dcf006
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/ptradd-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['call', 'print', ['ptradd', 'arr', 4, 3]]
+CodegenError: Bad ptradd expression: ['ptradd', 'arr', 4, 3]
diff --git a/src/backend/tests/c-lisp/errors/ptradd-bad.sexp b/src/backend/tests/c-lisp/errors/ptradd-bad.sexp
new file mode 100644
index 0000000..066a1df
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/ptradd-bad.sexp
@@ -0,0 +1,5 @@
+(c-lisp
+    (define ((main int))
+        (declare arr (ptr int))
+        (set arr (alloc int 20))
+        (call print (ptradd arr 4 3))))
diff --git a/src/backend/tests/c-lisp/errors/redeclare.out b/src/backend/tests/c-lisp/errors/redeclare.out
new file mode 100644
index 0000000..6814420
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/redeclare.out
@@ -0,0 +1,2 @@
+Error in statement: ['declare', 'var', 'bool']
+CodegenError: Re-declaration of variable var
diff --git a/src/backend/tests/c-lisp/errors/redeclare.sexp b/src/backend/tests/c-lisp/errors/redeclare.sexp
new file mode 100644
index 0000000..9d1dac6
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/redeclare.sexp
@@ -0,0 +1,9 @@
+(c-lisp
+    (define ((main void))
+        (declare var int)
+
+        (if #t
+            ((declare var float)
+             (set var 0.5)))
+
+        (declare var bool)))
diff --git a/src/backend/tests/c-lisp/errors/ret-bad.out b/src/backend/tests/c-lisp/errors/ret-bad.out
new file mode 100644
index 0000000..74c3607
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/ret-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['ret', 0, 1]
+CodegenError: Return statement can contain only 1 optional return value: ['ret', 0, 1]
diff --git a/src/backend/tests/c-lisp/errors/ret-bad.sexp b/src/backend/tests/c-lisp/errors/ret-bad.sexp
new file mode 100644
index 0000000..b0687ee
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/ret-bad.sexp
@@ -0,0 +1,3 @@
+(c-lisp
+    (define ((main int))
+        (ret 0 1)))
diff --git a/src/backend/tests/c-lisp/errors/scope.out b/src/backend/tests/c-lisp/errors/scope.out
new file mode 100644
index 0000000..ff124d4
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/scope.out
@@ -0,0 +1,2 @@
+Error in statement: ['call', 'print', 'val']
+CodegenError: Undeclared symbol: val
diff --git a/src/backend/tests/c-lisp/errors/scope.sexp b/src/backend/tests/c-lisp/errors/scope.sexp
new file mode 100644
index 0000000..a42ed8f
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/scope.sexp
@@ -0,0 +1,15 @@
+(c-lisp
+    (define ((print int) (n int)))
+
+    (define ((main void))
+        (declare i int)
+
+        (for ((set i 0)
+              (lt i 100)
+              (set i (add i 1)))
+            (declare val int)
+            (if (eq
+                    i
+                    (mul (div i 7) 7))
+                (set val i)))
+        (call print val)))
diff --git a/src/backend/tests/c-lisp/errors/set-bad.out b/src/backend/tests/c-lisp/errors/set-bad.out
new file mode 100644
index 0000000..d8a3ca3
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/set-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['set', ['declare', 'var', 'int'], 4]
+CodegenError: Bad set expression: ['set', ['declare', 'var', 'int'], 4]
diff --git a/src/backend/tests/c-lisp/errors/set-bad.sexp b/src/backend/tests/c-lisp/errors/set-bad.sexp
new file mode 100644
index 0000000..876d9e3
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/set-bad.sexp
@@ -0,0 +1,3 @@
+(c-lisp
+    (define ((main int))
+        (set (declare var int) 4)))
diff --git a/src/backend/tests/c-lisp/errors/store-bad.out b/src/backend/tests/c-lisp/errors/store-bad.out
new file mode 100644
index 0000000..eeb1d1c
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/store-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['store', 'a', 5, 6, 7]
+CodegenError: Bad store expression: ['store', 'a', 5, 6, 7]
diff --git a/src/backend/tests/c-lisp/errors/store-bad.sexp b/src/backend/tests/c-lisp/errors/store-bad.sexp
new file mode 100644
index 0000000..30e268b
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/store-bad.sexp
@@ -0,0 +1,5 @@
+(c-lisp
+    (define ((main void))
+        (declare a (ptr int))
+        (set a (alloc int 3))
+        (store a 5 6 7)))
diff --git a/src/backend/tests/c-lisp/errors/turnt.toml b/src/backend/tests/c-lisp/errors/turnt.toml
new file mode 100644
index 0000000..0a7454e
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/turnt.toml
@@ -0,0 +1 @@
+command = "guile ../../../utils/sexp-json.scm < {filename} | python ../../../c-lisp.py 2>&1 | sed -e '/^[ (Traceback)]/d'"
diff --git a/src/backend/tests/c-lisp/errors/undeclared-fn.out b/src/backend/tests/c-lisp/errors/undeclared-fn.out
new file mode 100644
index 0000000..1f38ce8
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/undeclared-fn.out
@@ -0,0 +1,2 @@
+Error in statement: ['call', 'print', 4]
+CodegenError: Call to undeclared function: print
diff --git a/src/backend/tests/c-lisp/errors/undeclared-fn.sexp b/src/backend/tests/c-lisp/errors/undeclared-fn.sexp
new file mode 100644
index 0000000..eeac15a
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/undeclared-fn.sexp
@@ -0,0 +1,3 @@
+(c-lisp
+    (define ((main int))
+        (call print 4)))
diff --git a/src/backend/tests/c-lisp/errors/undeclared-var.out b/src/backend/tests/c-lisp/errors/undeclared-var.out
new file mode 100644
index 0000000..29c1e34
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/undeclared-var.out
@@ -0,0 +1,2 @@
+Error in statement: ['set', 'var', 5]
+CodegenError: Undeclared symbol: var
diff --git a/src/backend/tests/c-lisp/errors/undeclared-var.sexp b/src/backend/tests/c-lisp/errors/undeclared-var.sexp
new file mode 100644
index 0000000..e6d7e80
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/undeclared-var.sexp
@@ -0,0 +1,4 @@
+(c-lisp
+    (define ((main int))
+        (set var 5)
+        (ret var)))
diff --git a/src/backend/tests/c-lisp/errors/while-bad.out b/src/backend/tests/c-lisp/errors/while-bad.out
new file mode 100644
index 0000000..3d9e5ce
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/while-bad.out
@@ -0,0 +1,2 @@
+Error in statement: ['while', ['call', 'print', 5]]
+CodegenError: Bad while statement: ['while', ['call', 'print', 5]]
diff --git a/src/backend/tests/c-lisp/errors/while-bad.sexp b/src/backend/tests/c-lisp/errors/while-bad.sexp
new file mode 100644
index 0000000..c768f34
--- /dev/null
+++ b/src/backend/tests/c-lisp/errors/while-bad.sexp
@@ -0,0 +1,4 @@
+(c-lisp
+    (define ((main int))
+        (while
+            (call print 5))))
diff --git a/src/backend/tests/c-lisp/for-return.out b/src/backend/tests/c-lisp/for-return.out
new file mode 100644
index 0000000..de2df04
--- /dev/null
+++ b/src/backend/tests/c-lisp/for-return.out
@@ -0,0 +1,3 @@
+12
+-2
+-1
diff --git a/src/backend/tests/c-lisp/for-return.sexp b/src/backend/tests/c-lisp/for-return.sexp
new file mode 100644
index 0000000..43e35d3
--- /dev/null
+++ b/src/backend/tests/c-lisp/for-return.sexp
@@ -0,0 +1,47 @@
+(c-lisp
+    (define ((print int) (n int)))
+
+    (define ((cons void) (arr (ptr int)) (n int))
+        (declare i int)
+        (for ((set i 0)
+              (lt i n)
+              (set i (add i 1)))
+            (store
+                (ptradd arr i)
+                (mul i 3))))
+
+    (define ((find int) (arr (ptr int)) (key int) (n int))
+        (declare i int)
+        (for ((set i 0)
+                (lt i n)
+                (set i (add i 1)))
+            (if (eq key
+                    (load (ptradd arr i)))
+                (ret i))))
+
+    (define ((verify int) (arr (ptr int)) (key int) (idx int) (len int))
+        (declare val int)
+        (if (lt idx len)
+            ((set val (load (ptradd arr idx)))
+             (if (eq val key)
+                 (ret val)
+                 (ret -1)))
+            (ret -2)))
+
+    (define ((main void))
+        (declare input (ptr int))
+        (declare i int)
+
+        (set input (alloc int 10))
+        (call cons input 10)
+
+        (declare 12-idx int)
+        (declare 13-idx int)
+
+        (set 12-idx (call find input 12 10))
+        (set 13-idx (call find input 13 10))
+
+        (call print (call verify input 12 12-idx 10))
+        (call print (call verify input 13 13-idx 10))
+        (call print (call verify input 12 2 10))
+        (ret)))
diff --git a/src/backend/utils/shape.py b/src/backend/utils/shape.py
new file mode 100644
index 0000000..d8590bd
--- /dev/null
+++ b/src/backend/utils/shape.py
@@ -0,0 +1,17 @@
+def verify_shape(obj, template):
+    """
+    Verify the shape of `lst` with `template`.
+    For example, ["set", "a", 5] has shape [str, str, int].
+    `None` can be used as a wildcard; so ["set", "a", ["add", 5, 1]] matches [str, str, None]
+    """
+    if template is None:
+        return True
+    elif not isinstance(template, list):
+        return isinstance(obj, template)
+    else:
+        if not isinstance(obj, list):
+            return False
+        for c in range(len(obj)):
+            if not verify_shape(obj[c], template[c]):
+                return False
+    return True