diff --git a/eval.c b/eval.c
index 69517750..6958b9ee 100644
--- a/eval.c
+++ b/eval.c
@@ -200,6 +200,7 @@ static sexp finalize_bytecode (sexp ctx) {
     else
       sexp_bytecode_literals(bc) = sexp_list_to_vector(ctx, sexp_bytecode_literals(bc));
   }
+  /* sexp_disasm(ctx, bc, sexp_current_error_port(ctx)); */
   return bc;
 }
 
@@ -277,19 +278,20 @@ static sexp sexp_make_lit (sexp ctx, sexp value) {
 #define SEXP_STACK_SIZE (sexp_sizeof(stack)+sizeof(sexp)*SEXP_INIT_STACK_SIZE)
 
 void sexp_init_eval_context_globals (sexp ctx) {
+  sexp_gc_var2(bc, vec);
   ctx = sexp_make_child_context(ctx, NULL);
+  sexp_gc_preserve2(ctx, bc, vec);
   emit(ctx, OP_RESUMECC);
   sexp_global(ctx, SEXP_G_RESUMECC_BYTECODE) = finalize_bytecode(ctx);
   ctx = sexp_make_child_context(ctx, NULL);
   emit(ctx, OP_DONE);
+  bc = finalize_bytecode(ctx);
+  vec = sexp_make_vector(ctx, 0, SEXP_VOID);
   sexp_global(ctx, SEXP_G_FINAL_RESUMER)
-    = sexp_make_procedure(ctx,
-                          sexp_make_fixnum(0),
-                          sexp_make_fixnum(0),
-                          finalize_bytecode(ctx),
-                          sexp_make_vector(ctx, 0, SEXP_VOID));
+    = sexp_make_procedure(ctx, SEXP_ZERO, SEXP_ZERO, bc, vec);
   sexp_bytecode_name(sexp_procedure_code(sexp_global(ctx, SEXP_G_FINAL_RESUMER)))
     = sexp_intern(ctx, "final-resumer");
+  sexp_gc_release2(ctx);
 }
 
 sexp sexp_make_eval_context (sexp ctx, sexp stack, sexp env) {
@@ -842,8 +844,7 @@ static void generate_set (sexp ctx, sexp set) {
     emit(ctx, OP_SET_CDR);
   } else {
     lambda = sexp_ref_loc(ref);
-    if (sexp_memq(ctx, sexp_ref_name(ref), sexp_lambda_sv(lambda))
-        != SEXP_FALSE) {
+    if (sexp_truep(sexp_memq(ctx, sexp_ref_name(ref), sexp_lambda_sv(lambda)))) {
       /* stack or closure mutable vars are boxed */
       generate_ref(ctx, ref, 0);
       emit(ctx, OP_SET_CDR);
@@ -1013,7 +1014,7 @@ static void generate_lambda (sexp ctx, sexp lambda) {
   sexp_bytecode_name(bc) = sexp_lambda_name(lambda);
   if (sexp_nullp(fv)) {
     /* shortcut, no free vars */
-    tmp = sexp_make_vector(ctx2, sexp_make_fixnum(0), SEXP_VOID);
+    tmp = sexp_make_vector(ctx2, SEXP_ZERO, SEXP_VOID);
     tmp = sexp_make_procedure(ctx2, flags, len, bc, tmp);
     sexp_push(ctx, sexp_bytecode_literals(sexp_context_bc(ctx)), tmp);
     generate_lit(ctx, tmp);
@@ -1161,8 +1162,7 @@ static sexp make_opcode_procedure (sexp ctx, sexp op, sexp_uint_t i) {
   generate_opcode_app(ctx2, refs);
   bc = finalize_bytecode(ctx2);
   sexp_bytecode_name(bc) = sexp_c_string(ctx2, sexp_opcode_name(op), -1);
-  res = sexp_make_procedure(ctx2, sexp_make_fixnum(0), sexp_make_fixnum(i),
-                            bc, SEXP_VOID);
+  res=sexp_make_procedure(ctx2, SEXP_ZERO, sexp_make_fixnum(i), bc, SEXP_VOID);
   if (i == sexp_opcode_num_args(op))
     sexp_opcode_proc(op) = res;
   sexp_gc_release5(ctx);
@@ -1268,20 +1268,18 @@ sexp sexp_vm (sexp ctx, sexp proc) {
     _ARG1 = tmp1;
     break;
   case OP_CALLCC:
-    stack[top] = sexp_make_fixnum(1);
+    stack[top] = SEXP_ONE;
     stack[top+1] = sexp_make_fixnum(ip-sexp_bytecode_data(bc));
     stack[top+2] = self;
     stack[top+3] = sexp_make_fixnum(fp);
     tmp1 = _ARG1;
     i = 1;
     sexp_context_top(ctx) = top;
-    tmp2 = sexp_make_vector(ctx, sexp_make_fixnum(1), SEXP_UNDEF);
-    sexp_vector_set(tmp2,
-                    sexp_make_fixnum(0),
-                    sexp_save_stack(ctx, stack, top+4));
+    tmp2 = sexp_make_vector(ctx, SEXP_ONE, SEXP_UNDEF);
+    sexp_vector_set(tmp2, SEXP_ZERO, sexp_save_stack(ctx, stack, top+4));
     _ARG1 = sexp_make_procedure(ctx,
-                                sexp_make_fixnum(0),
-                                sexp_make_fixnum(1),
+                                SEXP_ZERO,
+                                SEXP_ONE,
                                 sexp_global(ctx, SEXP_G_RESUMECC_BYTECODE),
                                 tmp2);
     top++;
@@ -1686,7 +1684,7 @@ sexp sexp_vm (sexp ctx, sexp proc) {
     top--;
     break;
   case OP_DIV:
-    if (_ARG2 == sexp_make_fixnum(0)) {
+    if (_ARG2 == SEXP_ZERO) {
 #if USE_FLONUMS
       if (sexp_flonump(_ARG1) && sexp_flonum_value(_ARG1) == 0.0)
         _ARG2 = sexp_make_flonum(ctx, 0.0/0.0);
@@ -1722,7 +1720,7 @@ sexp sexp_vm (sexp ctx, sexp proc) {
     break;
   case OP_QUOTIENT:
     if (sexp_fixnump(_ARG1) && sexp_fixnump(_ARG2)) {
-      if (_ARG2 == sexp_make_fixnum(0))
+      if (_ARG2 == SEXP_ZERO)
         sexp_raise("divide by zero", SEXP_NULL);
       _ARG2 = sexp_fx_div(_ARG1, _ARG2);
       top--;
@@ -1738,7 +1736,7 @@ sexp sexp_vm (sexp ctx, sexp proc) {
     break;
   case OP_REMAINDER:
     if (sexp_fixnump(_ARG1) && sexp_fixnump(_ARG2)) {
-      if (_ARG2 == sexp_make_fixnum(0))
+      if (_ARG2 == SEXP_ZERO)
         sexp_raise("divide by zero", SEXP_NULL);
       tmp1 = sexp_fx_rem(_ARG1, _ARG2);
       top--;
@@ -2117,9 +2115,9 @@ static sexp sexp_expt (sexp ctx, sexp x, sexp e) {
   sexp res;
 #if USE_BIGNUMS
   if (sexp_bignump(e)) {        /* bignum exponent needs special handling */
-    if ((x == sexp_make_fixnum(0)) || (x == sexp_make_fixnum(-1)))
+    if ((x == SEXP_ZERO) || (x == SEXP_NEG_ONE))
       res = sexp_make_flonum(ctx, pow(0, 0));          /* +nan.0 */
-    else if (x == sexp_make_fixnum(1))
+    else if (x == SEXP_ONE)
       res = sexp_make_flonum(ctx, 1);                  /* 1.0    */
     else if (sexp_flonump(x))
       res = sexp_make_flonum(ctx, pow(sexp_flonum_value(x), sexp_bignum_to_double(e)));
@@ -2187,6 +2185,21 @@ static sexp sexp_string_cmp (sexp ctx, sexp str1, sexp str2, sexp ci) {
 #include "opt/plan9.c"
 #endif
 
+/************************** optimizations *****************************/
+
+static sexp sexp_apply_optimization (sexp ctx, sexp proc, sexp ast) {
+  sexp res;
+  sexp_gc_var1(args);
+  if (sexp_opcodep(proc)) {
+    res = ((sexp_proc2)sexp_opcode_func(proc))(ctx, ast);
+  } else {
+    sexp_gc_preserve1(ctx, args);
+    res = sexp_apply(ctx, proc, args=sexp_list1(ctx, ast));
+    sexp_gc_release1(ctx);
+  }
+  return res;
+}
+
 /*********************** standard environment *************************/
 
 static struct sexp_struct core_forms[] = {
@@ -2290,10 +2303,8 @@ sexp sexp_make_type_predicate (sexp ctx, sexp name, sexp type) {
   if (! sexp_fixnump(type))
     return sexp_type_exception(ctx, "make-type-predicate: bad type", type);
   return sexp_make_opcode(ctx, name, sexp_make_fixnum(OPC_TYPE_PREDICATE),
-                          sexp_make_fixnum(OP_TYPEP), sexp_make_fixnum(1),
-                          sexp_make_fixnum(0), sexp_make_fixnum(0),
-                          sexp_make_fixnum(0), sexp_make_fixnum(0), type,
-                          NULL, NULL);
+                          sexp_make_fixnum(OP_TYPEP), SEXP_ONE, SEXP_ZERO,
+                          SEXP_ZERO, SEXP_ZERO, SEXP_ZERO, type, NULL, NULL);
 }
 
 sexp sexp_make_constructor (sexp ctx, sexp name, sexp type) {
@@ -2302,9 +2313,8 @@ sexp sexp_make_constructor (sexp ctx, sexp name, sexp type) {
     return sexp_type_exception(ctx, "make-constructor: bad type", type);
   type_size = sexp_type_size_base(&(sexp_type_specs[sexp_unbox_fixnum(type)]));
   return sexp_make_opcode(ctx, name, sexp_make_fixnum(OPC_CONSTRUCTOR),
-                          sexp_make_fixnum(OP_MAKE), sexp_make_fixnum(0),
-                          sexp_make_fixnum(0), sexp_make_fixnum(0),
-                          sexp_make_fixnum(0), sexp_make_fixnum(0), type,
+                          sexp_make_fixnum(OP_MAKE), SEXP_ZERO, SEXP_ZERO,
+                          SEXP_ZERO, SEXP_ZERO, SEXP_ZERO, type,
                           sexp_make_fixnum(type_size), NULL);
 }
 
@@ -2316,8 +2326,7 @@ sexp sexp_make_accessor (sexp ctx, sexp name, sexp type, sexp index, sexp code)
   return
     sexp_make_opcode(ctx, name, sexp_make_fixnum(OPC_ACCESSOR), code,
                      sexp_make_fixnum(sexp_unbox_fixnum(code)==OP_SLOT_REF?1:2),
-                     sexp_make_fixnum(0), type, sexp_make_fixnum(0),
-                     sexp_make_fixnum(0), type, index, NULL);
+                     SEXP_ZERO, type, SEXP_ZERO, SEXP_ZERO, type, index, NULL);
 }
 
 sexp sexp_make_getter (sexp ctx, sexp name, sexp type, sexp index) {
@@ -2376,6 +2385,7 @@ static sexp sexp_make_standard_env (sexp ctx, sexp version) {
   tmp = sexp_list1(ctx, sym=sexp_intern(ctx, sexp_platform));
   sexp_push(ctx, tmp, sym=sexp_intern(ctx, "chibi"));
   sexp_env_define(ctx, e, sexp_intern(ctx, "*features*"), tmp);
+  sexp_global(ctx, SEXP_G_OPTIMIZATIONS) = SEXP_NULL;
   sexp_gc_release4(ctx);
   return e;
 }
@@ -2426,9 +2436,9 @@ sexp sexp_apply (sexp ctx, sexp proc, sexp args) {
       stack[--offset] = sexp_car(ls);
     stack[top] = sexp_make_fixnum(len);
     top++;
-    stack[top++] = sexp_make_fixnum(0);
+    stack[top++] = SEXP_ZERO;
     stack[top++] = sexp_global(ctx, SEXP_G_FINAL_RESUMER);
-    stack[top++] = sexp_make_fixnum(0);
+    stack[top++] = SEXP_ZERO;
     sexp_context_top(ctx) = top;
     res = sexp_vm(ctx, proc);
     if (! res) res = SEXP_VOID;
@@ -2443,12 +2453,16 @@ sexp sexp_compile (sexp ctx, sexp x) {
   if (sexp_exceptionp(ast)) {
     res = ast;
   } else {
+#if USE_SIMPLIFY
+    res = sexp_global(ctx, SEXP_G_OPTIMIZATIONS);
+    for ( ; sexp_pairp(res); res=sexp_cdr(res))
+      ast = sexp_apply_optimization(ctx, sexp_cdar(res), ast);
+#endif
     free_vars(ctx, ast, SEXP_NULL);    /* should return SEXP_NULL */
     generate(ctx, ast);
     res = finalize_bytecode(ctx);
     vec = sexp_make_vector(ctx, 0, SEXP_VOID);
-    res = sexp_make_procedure(ctx, sexp_make_fixnum(0), sexp_make_fixnum(0),
-                              res, vec);
+    res = sexp_make_procedure(ctx, SEXP_ZERO, SEXP_ZERO, res, vec);
   }
   sexp_gc_release3(ctx);
   return res;
diff --git a/include/chibi/config.h b/include/chibi/config.h
index 61dd03b2..779847af 100644
--- a/include/chibi/config.h
+++ b/include/chibi/config.h
@@ -12,6 +12,9 @@
 /*   sexp_init_library(ctx, env) function provided. */
 /* #define USE_DL 0 */
 
+/* uncomment this to disable a simplifying optimization pass */
+/* #define USE_SIMPLIFY 0 */
+
 /* uncomment this to disable dynamic type definitions */
 /*   This enables register-simple-type and related */
 /*   opcodes for defining types, needed by the default */
@@ -161,6 +164,10 @@
 #endif
 #endif
 
+#ifndef USE_SIMPLIFY
+#define USE_SIMPLIFY 1
+#endif
+
 #ifndef USE_BOEHM
 #define USE_BOEHM 0
 #endif
diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index 88ae48d9..9e58e0b9 100644
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -455,6 +455,12 @@ sexp sexp_make_flonum(sexp ctx, double f);
 #define sexp_make_fixnum(n)    ((sexp) ((((sexp_sint_t)(n))<<SEXP_FIXNUM_BITS) + SEXP_FIXNUM_TAG))
 #define sexp_unbox_fixnum(n)   (((sexp_sint_t)(n))>>SEXP_FIXNUM_BITS)
 
+#define SEXP_NEG_ONE sexp_make_fixnum(-1)
+#define SEXP_ZERO    sexp_make_fixnum(0)
+#define SEXP_ONE     sexp_make_fixnum(1)
+#define SEXP_TWO     sexp_make_fixnum(2)
+#define SEXP_THREE   sexp_make_fixnum(3)
+
 #define sexp_make_character(n)  ((sexp) ((((sexp_sint_t)(n))<<SEXP_EXTENDED_BITS) + SEXP_CHAR_TAG))
 #define sexp_unbox_character(n) ((int) (((sexp_sint_t)(n))>>SEXP_EXTENDED_BITS))
 
@@ -576,6 +582,7 @@ SEXP_API sexp sexp_make_integer(sexp ctx, sexp_sint_t x);
 
 #define sexp_opcode_variadic_p(x)  (sexp_opcode_flags(x) & 1)
 #define sexp_opcode_opt_param_p(x) (sexp_opcode_flags(x) & 2)
+#define sexp_opcode_ref_trans_p(x) (sexp_opcode_flags(x) & 4)
 
 #define sexp_lambda_name(x)   ((x)->value.lambda.name)
 #define sexp_lambda_params(x) ((x)->value.lambda.params)
diff --git a/opt/debug.c b/opt/debug.c
index 6d8b5de6..97d46d7b 100644
--- a/opt/debug.c
+++ b/opt/debug.c
@@ -28,7 +28,13 @@ static sexp sexp_disasm (sexp ctx, sexp bc, sexp out) {
   } else if (! sexp_bytecodep(bc)) {
     return sexp_type_exception(ctx, "not a procedure", bc);
   }
+  if (! sexp_oportp(out))
+    return SEXP_VOID;
   ip = sexp_bytecode_data(bc);
+  sexp_write_string(ctx, "-------------- ", out);
+  if (sexp_truep(sexp_bytecode_name(bc)))
+    sexp_write(ctx, sexp_bytecode_name(bc), out);
+  sexp_write_char(ctx, '\n', out);
  loop:
   opcode = *ip++;
   if (opcode*sizeof(char*) < sizeof(reverse_opcode_names)) {
@@ -43,14 +49,16 @@ static sexp sexp_disasm (sexp ctx, sexp bc, sexp out) {
   case OP_CLOSURE_REF:
   case OP_JUMP:
   case OP_JUMP_UNLESS:
+  case OP_TYPEP:
   case OP_FCALL0:
   case OP_FCALL1:
   case OP_FCALL2:
   case OP_FCALL3:
-  case OP_TYPEP:
     sexp_printf(ctx, out, "%ld", (sexp_sint_t) ((sexp*)ip)[0]);
     ip += sizeof(sexp);
     break;
+    ip += sizeof(sexp);
+    break;
   case OP_SLOT_REF:
   case OP_SLOT_SET:
   case OP_MAKE:
diff --git a/sexp.c b/sexp.c
index 2432c264..f6d9d529 100644
--- a/sexp.c
+++ b/sexp.c
@@ -154,9 +154,8 @@ sexp sexp_register_simple_type (sexp ctx, sexp name, sexp slots) {
   short type_size = sexp_sizeof_header + sizeof(sexp)*sexp_unbox_fixnum(slots);
   return
     sexp_register_type(ctx, name, sexp_make_fixnum(sexp_offsetof_slot0),
-                       slots, slots, sexp_make_fixnum(0), sexp_make_fixnum(0),
-                       sexp_make_fixnum(type_size), sexp_make_fixnum(0),
-                       sexp_make_fixnum(0), NULL);
+                       slots, slots, SEXP_ZERO, SEXP_ZERO,
+                       sexp_make_fixnum(type_size), SEXP_ZERO, SEXP_ZERO, NULL);
 }
 
 sexp sexp_finalize_c_type (sexp ctx, sexp obj) {
@@ -323,8 +322,7 @@ sexp sexp_print_exception (sexp ctx, sexp exn, sexp out) {
     }
     if (sexp_pairp(sexp_exception_source(exn))) {
       ls = sexp_exception_source(exn);
-      if (sexp_fixnump(sexp_cdr(ls))
-          && (sexp_cdr(ls) >= sexp_make_fixnum(0))) {
+      if (sexp_fixnump(sexp_cdr(ls)) && (sexp_cdr(ls) >= SEXP_ZERO)) {
         sexp_write_string(ctx, " on line ", out);
         sexp_write(ctx, sexp_cdr(ls), out);
       }
@@ -743,8 +741,8 @@ sexp sexp_make_cpointer (sexp ctx, sexp_uint_t typeid, void *value, sexp parent,
 
 #if SEXP_BSD
 
-#define sexp_stream_ctx(vec) sexp_vector_ref((sexp)vec, sexp_make_fixnum(0))
-#define sexp_stream_buf(vec) sexp_vector_ref((sexp)vec, sexp_make_fixnum(1))
+#define sexp_stream_ctx(vec) sexp_vector_ref((sexp)vec, SEXP_ZERO)
+#define sexp_stream_buf(vec) sexp_vector_ref((sexp)vec, SEXP_ONE)
 #define sexp_stream_size(vec) sexp_vector_ref((sexp)vec, sexp_make_fixnum(2))
 #define sexp_stream_pos(vec) sexp_vector_ref((sexp)vec, sexp_make_fixnum(3))
 
@@ -801,7 +799,7 @@ sexp sexp_make_input_string_port (sexp ctx, sexp str) {
   sexp_stream_ctx(cookie) = ctx;
   sexp_stream_buf(cookie) = str;
   sexp_stream_size(cookie) = sexp_make_fixnum(sexp_string_length(str));
-  sexp_stream_pos(cookie) = sexp_make_fixnum(0);
+  sexp_stream_pos(cookie) = SEXP_ZERO;
   in = funopen(cookie, &sstream_read, NULL, &sstream_seek, NULL);
   res = sexp_make_input_port(ctx, in, SEXP_FALSE);
   sexp_port_cookie(res) = cookie;
@@ -819,7 +817,7 @@ sexp sexp_make_output_string_port (sexp ctx) {
   sexp_stream_ctx(cookie) = ctx;
   sexp_stream_buf(cookie) = sexp_make_string(ctx, size, SEXP_VOID);
   sexp_stream_size(cookie) = size;
-  sexp_stream_pos(cookie) = sexp_make_fixnum(0);
+  sexp_stream_pos(cookie) = SEXP_ZERO;
   out = funopen(cookie, NULL, &sstream_write, &sstream_seek, NULL);
   res = sexp_make_output_port(ctx, out, SEXP_FALSE);
   sexp_port_cookie(res) = cookie;
@@ -832,7 +830,7 @@ sexp sexp_get_output_string (sexp ctx, sexp port) {
   fflush(sexp_port_stream(port));
   return sexp_substring(ctx,
                         sexp_stream_buf(cookie),
-                        sexp_make_fixnum(0),
+                        SEXP_ZERO,
                         sexp_stream_pos(cookie));
 }
 
@@ -1530,7 +1528,7 @@ sexp sexp_read_raw (sexp ctx, sexp in) {
             sexp_bignum_sign(res) = -sexp_bignum_sign(res);
           else
 #endif
-            res = sexp_fx_mul(res, sexp_make_fixnum(-1));
+            res = sexp_fx_mul(res, SEXP_NEG_ONE);
       }
     } else {
       sexp_push_char(ctx, c2, in);