diff --git a/py/Makefile b/py/Makefile
index 4d36f3c9760e2badbcefa335dfbb32cc7506666e..764676f6b0d07c1391fe91be59832cabea0ec049 100644
--- a/py/Makefile
+++ b/py/Makefile
@@ -17,6 +17,7 @@ SRC = \
 	emitbc.c \
 	asmx64.c \
 	emitx64.c \
+	emitviperx64.c \
 	emitthumb.c \
 	asmthumb.c \
 	emitinlinethumb.c \
diff --git a/py/asmx64.c b/py/asmx64.c
index 4fbd44f98c2616a34474ec4ece6b032f1dd1e02e..c7e3cdc849182bc6ad06993d23d9f51afba7a735 100644
--- a/py/asmx64.c
+++ b/py/asmx64.c
@@ -441,6 +441,9 @@ void asm_x64_cmp_i32_with_r32(asm_x64_t* as, int src_i32, int src_r32) {
 }
 
 void asm_x64_test_r8_with_r8(asm_x64_t* as, int src_r64_a, int src_r64_b) {
+    // TODO implement for other registers
+    assert(src_r64_a == REG_RAX);
+    assert(src_r64_b == REG_RAX);
     asm_x64_write_byte_2(as, OPCODE_TEST_R8_WITH_RM8, MODRM_R64(src_r64_a) | MODRM_RM_REG | MODRM_RM_R64(src_r64_b));
 }
 
diff --git a/py/compile.c b/py/compile.c
index 924938e02eb4dae173b63aebe95fd86250cbaa10..9e90f82dd90285057f5e9a12ce1b24a53fb89000 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -31,7 +31,8 @@ typedef enum {
 #define EMIT_OPT_NONE           (0)
 #define EMIT_OPT_BYTE_CODE      (1)
 #define EMIT_OPT_NATIVE_PYTHON  (2)
-#define EMIT_OPT_ASM_THUMB      (3)
+#define EMIT_OPT_VIPER          (3)
+#define EMIT_OPT_ASM_THUMB      (4)
 
 typedef struct _compiler_t {
     qstr qstr___class__;
@@ -43,6 +44,7 @@ typedef struct _compiler_t {
     qstr qstr_assertion_error;
     qstr qstr_micropython;
     qstr qstr_native;
+    qstr qstr_viper;
     qstr qstr_asm_thumb;
 
     pass_kind_t pass;
@@ -764,6 +766,8 @@ static bool compile_built_in_decorator(compiler_t *comp, int name_len, py_parse_
     qstr attr = PY_PARSE_NODE_LEAF_ARG(name_nodes[1]);
     if (attr == comp->qstr_native) {
         *emit_options = EMIT_OPT_NATIVE_PYTHON;
+    } else if (attr == comp->qstr_viper) {
+        *emit_options = EMIT_OPT_VIPER;
     } else if (attr == comp->qstr_asm_thumb) {
         *emit_options = EMIT_OPT_ASM_THUMB;
     } else {
@@ -2640,6 +2644,7 @@ void py_compile(py_parse_node_t pn) {
     comp->qstr_assertion_error = qstr_from_str_static("AssertionError");
     comp->qstr_micropython = qstr_from_str_static("micropython");
     comp->qstr_native = qstr_from_str_static("native");
+    comp->qstr_viper = qstr_from_str_static("viper");
     comp->qstr_asm_thumb = qstr_from_str_static("asm_thumb");
 
     comp->break_label = 0;
@@ -2684,6 +2689,7 @@ void py_compile(py_parse_node_t pn) {
     // compile pass 2 and 3
     emit_t *emit_bc = NULL;
     emit_t *emit_native = NULL;
+    emit_t *emit_viper = NULL;
     emit_inline_asm_t *emit_inline_thumb = NULL;
     for (scope_t *s = comp->scope_head; s != NULL; s = s->next) {
         if (s->emit_options == EMIT_OPT_ASM_THUMB) {
@@ -2706,6 +2712,14 @@ void py_compile(py_parse_node_t pn) {
                     comp->emit_method_table = &emit_x64_method_table;
                     break;
 
+                case EMIT_OPT_VIPER:
+                    if (emit_viper == NULL) {
+                        emit_viper = emit_viper_x64_new(max_num_labels);
+                    }
+                    comp->emit = emit_viper;
+                    comp->emit_method_table = &emit_viper_x64_method_table;
+                    break;
+
                 default:
                     if (emit_bc == NULL) {
                         emit_bc = emit_bc_new(max_num_labels);
@@ -2714,6 +2728,8 @@ void py_compile(py_parse_node_t pn) {
                     comp->emit_method_table = &emit_bc_method_table;
                     break;
             }
+            //comp->emit = emit_cpython_new(max_num_labels);
+            //comp->emit_method_table = &emit_cpython_method_table;
             compile_scope(comp, s, PASS_2);
             compile_scope(comp, s, PASS_3);
         }
diff --git a/py/emit.h b/py/emit.h
index 221fdb37840c06d11eadb186b1d5c9999348c26c..74795b5ab83b6d03025fdeef4310cd316581297c 100644
--- a/py/emit.h
+++ b/py/emit.h
@@ -120,6 +120,7 @@ extern const emit_method_table_t emit_pass1_method_table;
 extern const emit_method_table_t emit_cpython_method_table;
 extern const emit_method_table_t emit_bc_method_table;
 extern const emit_method_table_t emit_x64_method_table;
+extern const emit_method_table_t emit_viper_x64_method_table;
 extern const emit_method_table_t emit_thumb_method_table;
 
 emit_t *emit_pass1_new(qstr qstr___class__);
@@ -127,6 +128,7 @@ void emit_pass1_free(emit_t *emit);
 emit_t *emit_cpython_new(uint max_num_labels);
 emit_t *emit_bc_new(uint max_num_labels);
 emit_t *emit_x64_new(uint max_num_labels);
+emit_t *emit_viper_x64_new(uint max_num_labels);
 emit_t *emit_thumb_new(uint max_num_labels);
 
 typedef struct _emit_inline_asm_t emit_inline_asm_t;
diff --git a/py/emitviperx64.c b/py/emitviperx64.c
new file mode 100644
index 0000000000000000000000000000000000000000..0d89cc64a3607875488287d59f1dd6515fb38053
--- /dev/null
+++ b/py/emitviperx64.c
@@ -0,0 +1,941 @@
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+#include "misc.h"
+#include "lexer.h"
+#include "machine.h"
+#include "parse.h"
+#include "scope.h"
+#include "runtime.h"
+#include "emit.h"
+#include "asmx64.h"
+
+#ifdef EMIT_ENABLE_X64
+
+#define REG_LOCAL_1 (REG_RBX)
+#define REG_LOCAL_NUM (1)
+
+typedef enum {
+    NEED_TO_PUSH_NOTHING,
+    NEED_TO_PUSH_R64,
+    NEED_TO_PUSH_I64,
+} need_to_push_t;
+
+typedef enum {
+    VTYPE_UNBOUND,
+    VTYPE_PYOBJ,
+    VTYPE_BOOL,
+    VTYPE_INT,
+    VTYPE_PTR,
+    VTYPE_PTR_NONE,
+    VTYPE_BUILTIN_V_INT,
+} vtype_kind_t;
+
+struct _emit_t {
+    int pass;
+
+    vtype_kind_t *all_vtype;
+    vtype_kind_t *local_vtype;
+    vtype_kind_t *stack_vtype;
+    int stack_start;
+    int stack_size;
+
+    bool last_emit_was_return_value;
+
+    need_to_push_t need_to_push;
+    vtype_kind_t last_vtype;
+    int last_r64;
+    int64_t last_i64;
+
+    scope_t *scope;
+
+    asm_x64_t *as;
+};
+
+emit_t *emit_viper_x64_new(uint max_num_labels) {
+    emit_t *emit = m_new(emit_t, 1);
+    emit->all_vtype = NULL;
+    emit->as = asm_x64_new(max_num_labels);
+    return emit;
+}
+
+static void emit_viper_x64_set_native_types(emit_t *emit, bool do_native_types) {
+    //emit->do_native_types = do_native_types;
+}
+
+static void emit_viper_x64_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scope) {
+    emit->pass = pass;
+    emit->stack_start = 0;
+    emit->stack_size = 0;
+    emit->last_emit_was_return_value = false;
+    emit->need_to_push = NEED_TO_PUSH_NOTHING;
+    emit->scope = scope;
+
+    if (emit->all_vtype == NULL) {
+        emit->all_vtype = m_new(vtype_kind_t, scope->num_locals + scope->stack_size + 100); // XXX don't know stack size on entry
+        emit->local_vtype = emit->all_vtype;
+        emit->stack_vtype = emit->all_vtype + scope->num_locals;
+        memset(emit->all_vtype, VTYPE_UNBOUND, sizeof(vtype_kind_t));
+    }
+
+    asm_x64_start_pass(emit->as, pass);
+
+    // entry to function
+    int num_locals = 0;
+    if (pass > PASS_1) {
+        num_locals = scope->num_locals - REG_LOCAL_NUM;
+        if (num_locals < 0) {
+            num_locals = 0;
+        }
+        emit->stack_start = num_locals;
+        num_locals += scope->stack_size;
+    }
+    asm_x64_entry(emit->as, num_locals);
+
+    // initialise locals from parameters
+    for (int i = 0; i < scope->num_params; i++) {
+        if (i == 0) {
+            asm_x64_mov_r64_to_r64(emit->as, REG_ARG_1, REG_LOCAL_1);
+        } else if (i == 1) {
+            asm_x64_mov_r64_to_local(emit->as, REG_ARG_2, i - 1);
+        } else if (i == 2) {
+            asm_x64_mov_r64_to_local(emit->as, REG_ARG_3, i - 1);
+        } else {
+            // TODO not implemented
+            assert(0);
+        }
+    }
+}
+
+static void emit_viper_x64_end_pass(emit_t *emit) {
+    if (!emit->last_emit_was_return_value) {
+        asm_x64_exit(emit->as);
+    }
+    asm_x64_end_pass(emit->as);
+
+    // check stack is back to zero size
+    if (emit->stack_size != 0) {
+        printf("ERROR: stack size not back to zero; got %d\n", emit->stack_size);
+    }
+
+    if (emit->pass == PASS_3) {
+        py_fun_t f = asm_x64_get_code(emit->as);
+        rt_assign_native_code(emit->scope->unique_code_id, f, asm_x64_get_code_size(emit->as), emit->scope->num_params);
+    }
+}
+
+static bool emit_viper_x64_last_emit_was_return_value(emit_t *emit) {
+    return emit->last_emit_was_return_value;
+}
+
+static int emit_viper_x64_get_stack_size(emit_t *emit) {
+    return emit->stack_size;
+}
+
+static void emit_viper_x64_set_stack_size(emit_t *emit, int size) {
+    emit->stack_size = size;
+}
+
+static void adjust_stack(emit_t *emit, int stack_size_delta) {
+    emit->stack_size += stack_size_delta;
+    assert(emit->stack_size >= 0);
+    if (emit->pass > PASS_1 && emit->stack_size > emit->scope->stack_size) {
+        emit->scope->stack_size = emit->stack_size;
+    }
+}
+
+static void stack_settle(emit_t *emit) {
+    switch (emit->need_to_push) {
+        case NEED_TO_PUSH_NOTHING:
+            break;
+
+        case NEED_TO_PUSH_R64:
+            emit->stack_vtype[emit->stack_size] = emit->last_vtype;
+            asm_x64_mov_r64_to_local(emit->as, emit->last_r64, emit->stack_start + emit->stack_size);
+            adjust_stack(emit, 1);
+            break;
+
+        case NEED_TO_PUSH_I64:
+            emit->stack_vtype[emit->stack_size] = emit->last_vtype;
+            asm_x64_mov_i64_to_r64_optimised(emit->as, emit->last_i64, REG_RAX);
+            asm_x64_mov_r64_to_local(emit->as, REG_RAX, emit->stack_start + emit->stack_size);
+            adjust_stack(emit, 1);
+            break;
+    }
+    emit->need_to_push = NEED_TO_PUSH_NOTHING;
+}
+
+static void emit_pre_raw(emit_t *emit, int stack_size_delta) {
+    adjust_stack(emit, stack_size_delta);
+    emit->last_emit_was_return_value = false;
+}
+
+static void emit_pre(emit_t *emit) {
+    stack_settle(emit);
+    emit_pre_raw(emit, 0);
+}
+
+static vtype_kind_t peek_vtype(emit_t *emit) {
+    switch (emit->need_to_push) {
+        case NEED_TO_PUSH_NOTHING:
+            return emit->stack_vtype[emit->stack_size - 1];
+
+        case NEED_TO_PUSH_R64:
+        case NEED_TO_PUSH_I64:
+            return emit->last_vtype;
+
+        default:
+            assert(0);
+            return VTYPE_UNBOUND;
+    }
+}
+
+static void emit_pre_pop_r64(emit_t *emit, vtype_kind_t *vtype, int r64) {
+    switch (emit->need_to_push) {
+        case NEED_TO_PUSH_NOTHING:
+            *vtype = emit->stack_vtype[emit->stack_size - 1];
+            asm_x64_mov_local_to_r64(emit->as, emit->stack_start + emit->stack_size - 1, r64);
+            emit_pre_raw(emit, -1);
+            break;
+
+        case NEED_TO_PUSH_R64:
+            emit_pre_raw(emit, 0);
+            *vtype = emit->last_vtype;
+            if (emit->last_r64 != r64) {
+                asm_x64_mov_r64_to_r64(emit->as, emit->last_r64, r64);
+            }
+            break;
+
+        case NEED_TO_PUSH_I64:
+            emit_pre_raw(emit, 0);
+            *vtype = emit->last_vtype;
+            asm_x64_mov_i64_to_r64_optimised(emit->as, emit->last_i64, r64);
+            break;
+    }
+    emit->need_to_push = NEED_TO_PUSH_NOTHING;
+}
+
+static void emit_pre_pop_r64_r64(emit_t *emit, vtype_kind_t *vtypea, int r64a, vtype_kind_t *vtypeb, int r64b) {
+    emit_pre_pop_r64(emit, vtypea, r64a);
+    *vtypeb = emit->stack_vtype[emit->stack_size - 1];
+    asm_x64_mov_local_to_r64(emit->as, emit->stack_start + emit->stack_size - 1, r64b);
+    adjust_stack(emit, -1);
+}
+
+static void emit_pre_pop_r64_r64_r64(emit_t *emit, vtype_kind_t *vtypea, int r64a, vtype_kind_t *vtypeb, int r64b, vtype_kind_t *vtypec, int r64c) {
+    emit_pre_pop_r64(emit, vtypea, r64a);
+    *vtypeb = emit->stack_vtype[emit->stack_size - 1];
+    asm_x64_mov_local_to_r64(emit->as, emit->stack_start + emit->stack_size - 1, r64b);
+    *vtypec = emit->stack_vtype[emit->stack_size - 2];
+    asm_x64_mov_local_to_r64(emit->as, emit->stack_start + emit->stack_size - 2, r64c);
+    adjust_stack(emit, -2);
+}
+
+static void emit_post(emit_t *emit) {
+}
+
+static void emit_post_push_r64(emit_t *emit, vtype_kind_t vtype, int r64) {
+    emit->need_to_push = NEED_TO_PUSH_R64;
+    emit->last_vtype = vtype;
+    emit->last_r64 = r64;
+}
+
+static void emit_post_push_i64(emit_t *emit, vtype_kind_t vtype, int64_t i64) {
+    emit->need_to_push = NEED_TO_PUSH_I64;
+    emit->last_vtype = vtype;
+    emit->last_i64 = i64;
+}
+
+static void emit_post_push_r64_r64(emit_t *emit, vtype_kind_t vtypea, int r64a, vtype_kind_t vtypeb, int r64b) {
+    emit->stack_vtype[emit->stack_size] = vtypea;
+    asm_x64_mov_r64_to_local(emit->as, r64a, emit->stack_start + emit->stack_size);
+    emit->need_to_push = NEED_TO_PUSH_R64;
+    emit->last_vtype = vtypeb;
+    emit->last_r64 = r64b;
+    adjust_stack(emit, 1);
+}
+
+static void emit_post_push_r64_r64_r64(emit_t *emit, vtype_kind_t vtypea, int r64a, vtype_kind_t vtypeb, int r64b, vtype_kind_t vtypec, int r64c) {
+    emit->stack_vtype[emit->stack_size] = vtypea;
+    asm_x64_mov_r64_to_local(emit->as, r64a, emit->stack_start + emit->stack_size);
+    emit->stack_vtype[emit->stack_size + 1] = vtypeb;
+    asm_x64_mov_r64_to_local(emit->as, r64b, emit->stack_start + emit->stack_size + 1);
+    emit->stack_vtype[emit->stack_size + 2] = vtypec;
+    asm_x64_mov_r64_to_local(emit->as, r64c, emit->stack_start + emit->stack_size + 2);
+    adjust_stack(emit, 3);
+}
+
+static void emit_post_push_r64_r64_r64_r64(emit_t *emit, vtype_kind_t vtypea, int r64a, vtype_kind_t vtypeb, int r64b, vtype_kind_t vtypec, int r64c, vtype_kind_t vtyped, int r64d) {
+    emit->stack_vtype[emit->stack_size] = vtypea;
+    asm_x64_mov_r64_to_local(emit->as, r64a, emit->stack_start + emit->stack_size);
+    emit->stack_vtype[emit->stack_size + 1] = vtypeb;
+    asm_x64_mov_r64_to_local(emit->as, r64b, emit->stack_start + emit->stack_size + 1);
+    emit->stack_vtype[emit->stack_size + 2] = vtypec;
+    asm_x64_mov_r64_to_local(emit->as, r64c, emit->stack_start + emit->stack_size + 2);
+    emit->stack_vtype[emit->stack_size + 3] = vtyped;
+    asm_x64_mov_r64_to_local(emit->as, r64d, emit->stack_start + emit->stack_size + 3);
+    adjust_stack(emit, 4);
+}
+
+// vtype of all n_pop objects is VTYPE_PYOBJ
+static void emit_get_stack_pointer_to_r64_for_pop(emit_t *emit, int r64, int n_pop) {
+    asm_x64_mov_local_addr_to_r64(emit->as, emit->stack_start + emit->stack_size - 1, r64);
+    adjust_stack(emit, -n_pop);
+}
+
+// vtype of all n_push objects is VTYPE_PYOBJ
+static void emit_get_stack_pointer_to_r64_for_push(emit_t *emit, int r64, int n_push) {
+    for (int i = 0; i < n_push; i++) {
+        emit->stack_vtype[emit->stack_size + i] = VTYPE_PYOBJ;
+    }
+    asm_x64_mov_local_addr_to_r64(emit->as, emit->stack_start + emit->stack_size + n_push - 1, r64);
+    adjust_stack(emit, n_push);
+}
+
+static void emit_call(emit_t *emit, void *fun) {
+    asm_x64_call_ind(emit->as, fun, REG_RAX);
+}
+
+static void emit_call_with_i64_arg(emit_t *emit, void *fun, int64_t arg_val, int arg_r64) {
+    asm_x64_mov_i64_to_r64_optimised(emit->as, arg_val, arg_r64);
+    asm_x64_call_ind(emit->as, fun, REG_RAX);
+}
+
+static void emit_viper_x64_load_id(emit_t *emit, qstr qstr) {
+    // check for built-ins
+    if (strcmp(qstr_str(qstr), "v_int") == 0) {
+        emit_pre(emit);
+        //emit_post_push_blank(emit, VTYPE_BUILTIN_V_INT);
+
+    // not a built-in, so do usual thing
+    } else {
+        emit_common_load_id(emit, &emit_viper_x64_method_table, emit->scope, qstr);
+    }
+}
+
+static void emit_viper_x64_store_id(emit_t *emit, qstr qstr) {
+    // TODO check for built-ins and disallow
+    emit_common_store_id(emit, &emit_viper_x64_method_table, emit->scope, qstr);
+}
+
+static void emit_viper_x64_delete_id(emit_t *emit, qstr qstr) {
+    // TODO check for built-ins and disallow
+    emit_common_delete_id(emit, &emit_viper_x64_method_table, emit->scope, qstr);
+}
+
+static void emit_viper_x64_label_assign(emit_t *emit, int l) {
+    asm_x64_label_assign(emit->as, l);
+}
+
+static void emit_viper_x64_import_name(emit_t *emit, qstr qstr) {
+    // not supported
+    assert(0);
+}
+
+static void emit_viper_x64_import_from(emit_t *emit, qstr qstr) {
+    // not supported
+    assert(0);
+}
+
+static void emit_viper_x64_import_star(emit_t *emit) {
+    // not supported
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_tok(emit_t *emit, py_token_kind_t tok) {
+    emit_pre(emit);
+    int vtype;
+    machine_uint_t val;
+    switch (tok) {
+        case PY_TOKEN_KW_NONE: vtype = VTYPE_PTR_NONE; val = 0; break;
+        case PY_TOKEN_KW_FALSE: vtype = VTYPE_BOOL; val = 0; break;
+        case PY_TOKEN_KW_TRUE: vtype = VTYPE_BOOL; val = 1; break;
+        default: assert(0); vtype = 0; val = 0; // shouldn't happen
+    }
+    emit_post_push_i64(emit, vtype, val);
+}
+
+static void emit_viper_x64_load_const_small_int(emit_t *emit, int arg) {
+    emit_pre(emit);
+    emit_post_push_i64(emit, VTYPE_INT, arg);
+}
+
+static void emit_viper_x64_load_const_int(emit_t *emit, qstr qstr) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_dec(emit_t *emit, qstr qstr) {
+    // not supported
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_id(emit_t *emit, qstr qstr) {
+    // not supported?
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_str(emit_t *emit, qstr qstr, bool bytes) {
+    // not implemented properly
+    assert(0);
+    emit_pre(emit);
+    emit_post_push_i64(emit, VTYPE_PTR, (machine_uint_t)qstr_str(qstr));
+}
+
+static void emit_viper_x64_load_const_verbatim_start(emit_t *emit) {
+    // not supported/needed
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_verbatim_int(emit_t *emit, int val) {
+    // not supported/needed
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_verbatim_str(emit_t *emit, const char *str) {
+    // not supported/needed
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_verbatim_strn(emit_t *emit, const char *str, int len) {
+    // not supported/needed
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_verbatim_quoted_str(emit_t *emit, qstr qstr, bool bytes) {
+    // not supported/needed
+    assert(0);
+}
+
+static void emit_viper_x64_load_const_verbatim_end(emit_t *emit) {
+    // not supported/needed
+    assert(0);
+}
+
+static void emit_viper_x64_load_fast(emit_t *emit, qstr qstr, int local_num) {
+    if (emit->local_vtype[local_num] == VTYPE_UNBOUND) {
+        printf("ViperTypeError: local %s used before type known\n", qstr_str(qstr));
+    }
+    if (local_num == 0) {
+        emit_pre(emit);
+        emit_post_push_r64(emit, emit->local_vtype[local_num], REG_LOCAL_1);
+    } else {
+        emit_pre(emit);
+        asm_x64_mov_local_to_r64(emit->as, local_num - 1, REG_RAX);
+        emit_post_push_r64(emit, emit->local_vtype[local_num], REG_RAX);
+    }
+}
+
+static void emit_viper_x64_load_name(emit_t *emit, qstr qstr) {
+    emit_pre(emit);
+    emit_call_with_i64_arg(emit, rt_load_name, qstr, REG_ARG_1);
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+}
+
+static void emit_viper_x64_load_global(emit_t *emit, qstr qstr) {
+    emit_pre(emit);
+    emit_call_with_i64_arg(emit, rt_load_global, qstr, REG_ARG_1);
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+}
+
+static void emit_viper_x64_load_deref(emit_t *emit, qstr qstr) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_load_closure(emit_t *emit, qstr qstr) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_load_attr(emit_t *emit, qstr qstr) {
+    vtype_kind_t vtype_base;
+    emit_pre_pop_r64(emit, &vtype_base, REG_ARG_1); // arg1 = base
+    assert(vtype_base == VTYPE_PYOBJ);
+    emit_call_with_i64_arg(emit, rt_load_attr, qstr, REG_ARG_2); // arg2 = attribute name
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+}
+
+static void emit_viper_x64_load_method(emit_t *emit, qstr qstr) {
+    vtype_kind_t vtype_base;
+    emit_pre_pop_r64(emit, &vtype_base, REG_ARG_1); // arg1 = base
+    assert(vtype_base == VTYPE_PYOBJ);
+    emit_get_stack_pointer_to_r64_for_push(emit, REG_ARG_3, 2); // arg3 = dest ptr
+    emit_call_with_i64_arg(emit, rt_load_method, qstr, REG_ARG_2); // arg2 = method name
+}
+
+static void emit_viper_x64_load_build_class(emit_t *emit) {
+    // not supported
+   assert(0);
+}
+
+static void emit_viper_x64_store_fast(emit_t *emit, qstr qstr, int local_num) {
+    vtype_kind_t vtype;
+    if (local_num == 0) {
+        emit_pre_pop_r64(emit, &vtype, REG_LOCAL_1);
+        emit_post(emit);
+    } else {
+        emit_pre_pop_r64(emit, &vtype, REG_RAX);
+        asm_x64_mov_r64_to_local(emit->as, REG_RAX, local_num - 1);
+        emit_post(emit);
+    }
+
+    // check types
+    if (emit->local_vtype[local_num] == VTYPE_UNBOUND) {
+        // first time this local is assigned, so give it a type of the object stored in it
+        emit->local_vtype[local_num] = vtype;
+    } else if (emit->local_vtype[local_num] != vtype) {
+        // type of local is not the same as object stored in it
+        printf("ViperTypeError: type mismatch, local %s has type %d but source object has type %d\n", qstr_str(qstr), emit->local_vtype[local_num], vtype);
+    }
+}
+
+static void emit_viper_x64_store_name(emit_t *emit, qstr qstr) {
+    vtype_kind_t vtype;
+    emit_pre_pop_r64(emit, &vtype, REG_ARG_2);
+    assert(vtype == VTYPE_PYOBJ);
+    emit_call_with_i64_arg(emit, rt_store_name, qstr, REG_ARG_1); // arg1 = name
+    emit_post(emit);
+}
+
+static void emit_viper_x64_store_global(emit_t *emit, qstr qstr) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_store_deref(emit_t *emit, qstr qstr) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_store_attr(emit_t *emit, qstr qstr) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_store_locals(emit_t *emit) {
+    // not supported
+    assert(0);
+}
+
+static void emit_viper_x64_store_subscr(emit_t *emit) {
+    vtype_kind_t vtype_index, vtype_base, vtype_value;
+    emit_pre_pop_r64_r64_r64(emit, &vtype_index, REG_ARG_2, &vtype_base, REG_ARG_1, &vtype_value, REG_ARG_3); // index, base, value to store
+    assert(vtype_index == VTYPE_PYOBJ);
+    assert(vtype_base == VTYPE_PYOBJ);
+    assert(vtype_value == VTYPE_PYOBJ);
+    emit_call(emit, rt_store_subscr);
+}
+
+static void emit_viper_x64_delete_fast(emit_t *emit, qstr qstr, int local_num) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_delete_name(emit_t *emit, qstr qstr) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_delete_global(emit_t *emit, qstr qstr) {
+    // not implemented
+    assert(0);
+}
+
+static void emit_viper_x64_delete_deref(emit_t *emit, qstr qstr) {
+    // not supported
+    assert(0);
+}
+
+static void emit_viper_x64_delete_attr(emit_t *emit, qstr qstr) {
+    // not supported
+    assert(0);
+}
+
+static void emit_viper_x64_delete_subscr(emit_t *emit) {
+    // not supported
+    assert(0);
+}
+
+static void emit_viper_x64_dup_top(emit_t *emit) {
+    vtype_kind_t vtype;
+    emit_pre_pop_r64(emit, &vtype, REG_RAX);
+    emit_post_push_r64_r64(emit, vtype, REG_RAX, vtype, REG_RAX);
+}
+
+static void emit_viper_x64_dup_top_two(emit_t *emit) {
+    vtype_kind_t vtype1, vtype2;
+    emit_pre_pop_r64_r64(emit, &vtype1, REG_RAX, &vtype2, REG_RDI);
+    emit_post_push_r64_r64_r64_r64(emit, vtype2, REG_RDI, vtype1, REG_RAX, vtype2, REG_RDI, vtype1, REG_RAX);
+}
+
+static void emit_viper_x64_pop_top(emit_t *emit) {
+    vtype_kind_t vtype;
+    emit_pre_pop_r64(emit, &vtype, REG_RAX);
+    emit_post(emit);
+}
+
+static void emit_viper_x64_rot_two(emit_t *emit) {
+    assert(0);
+}
+
+static void emit_viper_x64_rot_three(emit_t *emit) {
+    vtype_kind_t vtype_rax, vtype_rdi, vtype_rsi;
+    emit_pre_pop_r64_r64_r64(emit, &vtype_rax, REG_RAX, &vtype_rdi, REG_RDI, &vtype_rsi, REG_RSI);
+    emit_post_push_r64_r64_r64(emit, vtype_rax, REG_RAX, vtype_rsi, REG_RSI, vtype_rdi, REG_RDI);
+}
+
+static void emit_viper_x64_jump(emit_t *emit, int label) {
+    emit_pre(emit);
+    asm_x64_jmp_label(emit->as, label);
+    emit_post(emit);
+}
+
+static void emit_viper_x64_pop_jump_if_false(emit_t *emit, int label) {
+    vtype_kind_t vtype = peek_vtype(emit);
+    if (vtype == VTYPE_BOOL) {
+        emit_pre_pop_r64(emit, &vtype, REG_RAX);
+        asm_x64_test_r8_with_r8(emit->as, REG_RAX, REG_RAX);
+        asm_x64_jcc_label(emit->as, JCC_JZ, label);
+        emit_post(emit);
+    } else if (vtype == VTYPE_PYOBJ) {
+        emit_pre_pop_r64(emit, &vtype, REG_ARG_1);
+        emit_call(emit, rt_is_true);
+        asm_x64_test_r8_with_r8(emit->as, REG_RET, REG_RET);
+        asm_x64_jcc_label(emit->as, JCC_JZ, label);
+        emit_post(emit);
+    } else {
+        printf("ViperTypeError: expecting a bool or pyobj, got %d\n", vtype);
+        assert(0);
+    }
+}
+
+static void emit_viper_x64_pop_jump_if_true(emit_t *emit, int label) {
+    assert(0);
+}
+static void emit_viper_x64_jump_if_true_or_pop(emit_t *emit, int label) {
+    assert(0);
+}
+static void emit_viper_x64_jump_if_false_or_pop(emit_t *emit, int label) {
+    assert(0);
+}
+
+static void emit_viper_x64_setup_loop(emit_t *emit, int label) {
+    emit_pre(emit);
+    emit_post(emit);
+}
+
+static void emit_viper_x64_break_loop(emit_t *emit, int label) {
+    assert(0);
+}
+static void emit_viper_x64_continue_loop(emit_t *emit, int label) {
+    assert(0);
+}
+static void emit_viper_x64_setup_with(emit_t *emit, int label) {
+    assert(0);
+}
+static void emit_viper_x64_with_cleanup(emit_t *emit) {
+    assert(0);
+}
+static void emit_viper_x64_setup_except(emit_t *emit, int label) {
+    assert(0);
+}
+static void emit_viper_x64_setup_finally(emit_t *emit, int label) {
+    assert(0);
+}
+static void emit_viper_x64_end_finally(emit_t *emit) {
+    assert(0);
+}
+static void emit_viper_x64_get_iter(emit_t *emit) {
+    assert(0);
+} // tos = getiter(tos)
+static void emit_viper_x64_for_iter(emit_t *emit, int label) {
+    assert(0);
+}
+static void emit_viper_x64_for_iter_end(emit_t *emit) {
+    assert(0);
+}
+static void emit_viper_x64_pop_except(emit_t *emit) {
+    assert(0);
+}
+
+static void emit_viper_x64_unary_op(emit_t *emit, rt_unary_op_t op) {
+    vtype_kind_t vtype;
+    emit_pre_pop_r64(emit, &vtype, REG_ARG_2);
+    assert(vtype == VTYPE_PYOBJ);
+    emit_call_with_i64_arg(emit, rt_unary_op, op, REG_ARG_1);
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+}
+
+static void emit_viper_x64_build_tuple(emit_t *emit, int n_args) {
+    assert(0);
+}
+
+static void emit_viper_x64_build_list(emit_t *emit, int n_args) {
+    emit_pre(emit);
+    emit_get_stack_pointer_to_r64_for_pop(emit, REG_ARG_2, n_args); // pointer to items in reverse order
+    emit_call_with_i64_arg(emit, rt_build_list, n_args, REG_ARG_1);
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET); // new list
+}
+
+static void emit_viper_x64_list_append(emit_t *emit, int list_index) {
+    assert(0);
+}
+
+static void emit_viper_x64_build_map(emit_t *emit, int n_args) {
+    emit_pre(emit);
+    emit_call_with_i64_arg(emit, rt_build_map, n_args, REG_ARG_1);
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET); // new map
+}
+
+static void emit_viper_x64_store_map(emit_t *emit) {
+    vtype_kind_t vtype_key, vtype_value, vtype_map;
+    emit_pre_pop_r64_r64_r64(emit, &vtype_key, REG_ARG_2, &vtype_value, REG_ARG_3, &vtype_map, REG_ARG_1); // key, value, map
+    assert(vtype_key == VTYPE_PYOBJ);
+    assert(vtype_value == VTYPE_PYOBJ);
+    assert(vtype_map == VTYPE_PYOBJ);
+    emit_call(emit, rt_store_map);
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET); // map
+}
+
+static void emit_viper_x64_map_add(emit_t *emit, int map_index) {
+    assert(0);
+}
+
+static void emit_viper_x64_build_set(emit_t *emit, int n_args) {
+    emit_pre(emit);
+    emit_get_stack_pointer_to_r64_for_pop(emit, REG_ARG_2, n_args); // pointer to items in reverse order
+    emit_call_with_i64_arg(emit, rt_build_set, n_args, REG_ARG_1);
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET); // new set
+}
+
+static void emit_viper_x64_set_add(emit_t *emit, int set_index) {
+    assert(0);
+}
+static void emit_viper_x64_build_slice(emit_t *emit, int n_args) {
+    assert(0);
+}
+static void emit_viper_x64_unpack_sequence(emit_t *emit, int n_args) {
+    assert(0);
+}
+static void emit_viper_x64_unpack_ex(emit_t *emit, int n_left, int n_right) {
+    assert(0);
+}
+
+static void emit_viper_x64_make_function(emit_t *emit, scope_t *scope, int n_dict_params, int n_default_params) {
+    assert(n_default_params == 0 && n_dict_params == 0);
+    emit_pre(emit);
+    emit_call_with_i64_arg(emit, rt_make_function_from_id, scope->unique_code_id, REG_ARG_1);
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+}
+
+static void emit_viper_x64_make_closure(emit_t *emit, scope_t *scope, int n_dict_params, int n_default_params) {
+    assert(0);
+}
+
+static void emit_viper_x64_call_function(emit_t *emit, int n_positional, int n_keyword, bool have_star_arg, bool have_dbl_star_arg) {
+    assert(n_keyword == 0 && !have_star_arg && !have_dbl_star_arg);
+    if (n_positional == 0) {
+        vtype_kind_t vtype_fun;
+        emit_pre_pop_r64(emit, &vtype_fun, REG_ARG_1); // the function
+        assert(vtype_fun == VTYPE_PYOBJ);
+        emit_call(emit, rt_call_function_0);
+    } else if (n_positional == 1) {
+        vtype_kind_t vtype_fun, vtype_arg1;
+        emit_pre_pop_r64_r64(emit, &vtype_arg1, REG_ARG_2, &vtype_fun, REG_ARG_1); // the single argument, the function
+        assert(vtype_fun == VTYPE_PYOBJ);
+        assert(vtype_arg1 == VTYPE_PYOBJ);
+        emit_call(emit, rt_call_function_1);
+    } else if (n_positional == 2) {
+        vtype_kind_t vtype_fun, vtype_arg1, vtype_arg2;
+        emit_pre_pop_r64_r64_r64(emit, &vtype_arg2, REG_ARG_3, &vtype_arg1, REG_ARG_2, &vtype_fun, REG_ARG_1); // the second argument, the first argument, the function
+        assert(vtype_fun == VTYPE_PYOBJ);
+        assert(vtype_arg1 == VTYPE_PYOBJ);
+        assert(vtype_arg2 == VTYPE_PYOBJ);
+        emit_call(emit, rt_call_function_2);
+    } else {
+        assert(0);
+    }
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+}
+
+static void emit_viper_x64_call_method(emit_t *emit, int n_positional, int n_keyword, bool have_star_arg, bool have_dbl_star_arg) {
+    assert(n_keyword == 0 && !have_star_arg && !have_dbl_star_arg);
+    if (n_positional == 0) {
+        vtype_kind_t vtype_meth, vtype_self;
+        emit_pre_pop_r64_r64(emit, &vtype_self, REG_ARG_2, &vtype_meth, REG_ARG_1); // the self object (or NULL), the method
+        assert(vtype_meth == VTYPE_PYOBJ);
+        assert(vtype_self == VTYPE_PYOBJ);
+        emit_call(emit, rt_call_method_1);
+    } else if (n_positional == 1) {
+        vtype_kind_t vtype_meth, vtype_self, vtype_arg1;
+        emit_pre_pop_r64_r64_r64(emit, &vtype_arg1, REG_ARG_3, &vtype_self, REG_ARG_2, &vtype_meth, REG_ARG_1); // the first argument, the self object (or NULL), the method
+        assert(vtype_meth == VTYPE_PYOBJ);
+        assert(vtype_self == VTYPE_PYOBJ);
+        assert(vtype_arg1 == VTYPE_PYOBJ);
+        emit_call(emit, rt_call_method_2);
+    } else {
+        assert(0);
+    }
+    emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+}
+
+static void emit_viper_x64_pop_block(emit_t *emit) {
+    emit_pre(emit);
+    emit_post(emit);
+}
+
+static void emit_viper_x64_binary_op(emit_t *emit, rt_binary_op_t op) {
+    vtype_kind_t vtype_lhs, vtype_rhs;
+    emit_pre_pop_r64_r64(emit, &vtype_rhs, REG_ARG_3, &vtype_lhs, REG_ARG_2);
+    if (vtype_lhs == VTYPE_INT && vtype_rhs == VTYPE_INT) {
+        assert(op == RT_BINARY_OP_ADD);
+        asm_x64_add_r64_to_r64(emit->as, REG_ARG_3, REG_ARG_2);
+        emit_post_push_r64(emit, VTYPE_INT, REG_ARG_2);
+    } else if (vtype_lhs == VTYPE_PYOBJ && vtype_rhs == VTYPE_PYOBJ) {
+        emit_call_with_i64_arg(emit, rt_binary_op, op, REG_ARG_1);
+        emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+    } else {
+        printf("ViperTypeError: can't do binary op between types %d and %d\n", vtype_lhs, vtype_rhs);
+        assert(0);
+    }
+}
+
+static void emit_viper_x64_compare_op(emit_t *emit, rt_compare_op_t op) {
+    vtype_kind_t vtype_lhs, vtype_rhs;
+    emit_pre_pop_r64_r64(emit, &vtype_rhs, REG_ARG_3, &vtype_lhs, REG_ARG_2);
+    if (vtype_lhs == VTYPE_INT && vtype_rhs == VTYPE_INT) {
+        assert(op == RT_COMPARE_OP_LESS);
+        asm_x64_xor_r64_to_r64(emit->as, REG_RET, REG_RET);
+        asm_x64_cmp_r64_with_r64(emit->as, REG_ARG_3, REG_ARG_2);
+        asm_x64_setcc_r8(emit->as, JCC_JL, REG_RET);
+        emit_post_push_r64(emit, VTYPE_BOOL, REG_RET);
+    } else if (vtype_lhs == VTYPE_PYOBJ && vtype_rhs == VTYPE_PYOBJ) {
+        emit_call_with_i64_arg(emit, rt_compare_op, op, REG_ARG_1);
+        emit_post_push_r64(emit, VTYPE_PYOBJ, REG_RET);
+    } else {
+        printf("ViperTypeError: can't do comparison between types %d and %d\n", vtype_lhs, vtype_rhs);
+        assert(0);
+    }
+}
+
+static void emit_viper_x64_return_value(emit_t *emit) {
+    vtype_kind_t vtype;
+    emit_pre_pop_r64(emit, &vtype, REG_RAX);
+    assert(vtype == VTYPE_PTR_NONE);
+    emit->last_emit_was_return_value = true;
+    //asm_x64_call_ind(emit->as, 0, REG_RAX); to seg fault for debugging with gdb
+    asm_x64_exit(emit->as);
+}
+
+static void emit_viper_x64_raise_varargs(emit_t *emit, int n_args) {
+    assert(0);
+}
+static void emit_viper_x64_yield_value(emit_t *emit) {
+    assert(0);
+}
+static void emit_viper_x64_yield_from(emit_t *emit) {
+    assert(0);
+}
+
+const emit_method_table_t emit_viper_x64_method_table = {
+    emit_viper_x64_set_native_types,
+    emit_viper_x64_start_pass,
+    emit_viper_x64_end_pass,
+    emit_viper_x64_last_emit_was_return_value,
+    emit_viper_x64_get_stack_size,
+    emit_viper_x64_set_stack_size,
+
+    emit_viper_x64_load_id,
+    emit_viper_x64_store_id,
+    emit_viper_x64_delete_id,
+
+    emit_viper_x64_label_assign,
+    emit_viper_x64_import_name,
+    emit_viper_x64_import_from,
+    emit_viper_x64_import_star,
+    emit_viper_x64_load_const_tok,
+    emit_viper_x64_load_const_small_int,
+    emit_viper_x64_load_const_int,
+    emit_viper_x64_load_const_dec,
+    emit_viper_x64_load_const_id,
+    emit_viper_x64_load_const_str,
+    emit_viper_x64_load_const_verbatim_start,
+    emit_viper_x64_load_const_verbatim_int,
+    emit_viper_x64_load_const_verbatim_str,
+    emit_viper_x64_load_const_verbatim_strn,
+    emit_viper_x64_load_const_verbatim_quoted_str,
+    emit_viper_x64_load_const_verbatim_end,
+    emit_viper_x64_load_fast,
+    emit_viper_x64_load_name,
+    emit_viper_x64_load_global,
+    emit_viper_x64_load_deref,
+    emit_viper_x64_load_closure,
+    emit_viper_x64_load_attr,
+    emit_viper_x64_load_method,
+    emit_viper_x64_load_build_class,
+    emit_viper_x64_store_fast,
+    emit_viper_x64_store_name,
+    emit_viper_x64_store_global,
+    emit_viper_x64_store_deref,
+    emit_viper_x64_store_attr,
+    emit_viper_x64_store_locals,
+    emit_viper_x64_store_subscr,
+    emit_viper_x64_delete_fast,
+    emit_viper_x64_delete_name,
+    emit_viper_x64_delete_global,
+    emit_viper_x64_delete_deref,
+    emit_viper_x64_delete_attr,
+    emit_viper_x64_delete_subscr,
+    emit_viper_x64_dup_top,
+    emit_viper_x64_dup_top_two,
+    emit_viper_x64_pop_top,
+    emit_viper_x64_rot_two,
+    emit_viper_x64_rot_three,
+    emit_viper_x64_jump,
+    emit_viper_x64_pop_jump_if_true,
+    emit_viper_x64_pop_jump_if_false,
+    emit_viper_x64_jump_if_true_or_pop,
+    emit_viper_x64_jump_if_false_or_pop,
+    emit_viper_x64_setup_loop,
+    emit_viper_x64_break_loop,
+    emit_viper_x64_continue_loop,
+    emit_viper_x64_setup_with,
+    emit_viper_x64_with_cleanup,
+    emit_viper_x64_setup_except,
+    emit_viper_x64_setup_finally,
+    emit_viper_x64_end_finally,
+    emit_viper_x64_get_iter,
+    emit_viper_x64_for_iter,
+    emit_viper_x64_for_iter_end,
+    emit_viper_x64_pop_block,
+    emit_viper_x64_pop_except,
+    emit_viper_x64_unary_op,
+    emit_viper_x64_binary_op,
+    emit_viper_x64_compare_op,
+    emit_viper_x64_build_tuple,
+    emit_viper_x64_build_list,
+    emit_viper_x64_list_append,
+    emit_viper_x64_build_map,
+    emit_viper_x64_store_map,
+    emit_viper_x64_map_add,
+    emit_viper_x64_build_set,
+    emit_viper_x64_set_add,
+    emit_viper_x64_build_slice,
+    emit_viper_x64_unpack_sequence,
+    emit_viper_x64_unpack_ex,
+    emit_viper_x64_make_function,
+    emit_viper_x64_make_closure,
+    emit_viper_x64_call_function,
+    emit_viper_x64_call_method,
+    emit_viper_x64_return_value,
+    emit_viper_x64_raise_varargs,
+    emit_viper_x64_yield_value,
+    emit_viper_x64_yield_from,
+};
+
+#endif // EMIT_ENABLE_X64
diff --git a/py/emitx64.c b/py/emitx64.c
index 8ed617f2b0daf6b1d8c9a7081160b858b4c568de..5af5614385df4f5a661044a81f0a33ae5558649b 100644
--- a/py/emitx64.c
+++ b/py/emitx64.c
@@ -130,18 +130,6 @@ static void emit_x64_set_stack_size(emit_t *emit, int size) {
     emit->stack_size = size;
 }
 
-static void emit_x64_load_id(emit_t *emit, qstr qstr) {
-    emit_common_load_id(emit, &emit_x64_method_table, emit->scope, qstr);
-}
-
-static void emit_x64_store_id(emit_t *emit, qstr qstr) {
-    emit_common_store_id(emit, &emit_x64_method_table, emit->scope, qstr);
-}
-
-static void emit_x64_delete_id(emit_t *emit, qstr qstr) {
-    emit_common_delete_id(emit, &emit_x64_method_table, emit->scope, qstr);
-}
-
 static void adjust_stack(emit_t *emit, int stack_size_delta) {
     emit->stack_size += stack_size_delta;
     assert(emit->stack_size >= 0);
@@ -268,6 +256,18 @@ static void emit_call_with_i64_arg(emit_t *emit, void *fun, int64_t arg_val, int
     asm_x64_call_ind(emit->as, fun, REG_RAX);
 }
 
+static void emit_x64_load_id(emit_t *emit, qstr qstr) {
+    emit_common_load_id(emit, &emit_x64_method_table, emit->scope, qstr);
+}
+
+static void emit_x64_store_id(emit_t *emit, qstr qstr) {
+    emit_common_store_id(emit, &emit_x64_method_table, emit->scope, qstr);
+}
+
+static void emit_x64_delete_id(emit_t *emit, qstr qstr) {
+    emit_common_delete_id(emit, &emit_x64_method_table, emit->scope, qstr);
+}
+
 static void emit_x64_label_assign(emit_t *emit, int l) {
     asm_x64_label_assign(emit->as, l);
 }