diff --git a/examples/assembly.dst b/examples/assembly.dst
new file mode 100644
index 00000000..d027e935
--- /dev/null
+++ b/examples/assembly.dst
@@ -0,0 +1,22 @@
+# Example of dst assembly
+
+# Fibonacci sequence, implemented with naive recursion.
+(def fibasm (asm '{
+  arity 1
+  bytecode [
+    (ldi 1 0x2)          # $1 = 2
+    (lt 1 0 1)          # $1 = $0 < $1
+    (jmpn 1 :recursive) # if (not $1) goto :recursive
+    (ret 0)             # return $0
+    :recursive
+    (lds 1)              # $1 = self
+    (addim 0 0 -0x1)    # $0 = $0 - 1
+    (push 0)            # push($0)
+    (call 2 1)          # $2 = call($1)
+    (addim 0 0 -0x1)    # $0 = $0 - 1
+    (push 0)            # push($0)
+    (call 0 1)          # $0 = call($1)
+    (addi 0 0 2)        # $0 = $0 + $2 (integers)
+    (ret 0)             # return $0
+  ]
+}))
diff --git a/src/assembler/asm.c b/src/assembler/asm.c
index 74c5088f..db8a8b62 100644
--- a/src/assembler/asm.c
+++ b/src/assembler/asm.c
@@ -56,6 +56,7 @@ struct DstAssembler {
     DstFuncDef *def;
     jmp_buf on_error;
     const uint8_t *errmessage;
+    int32_t errindex;
 
     int32_t environments_capacity;
     int32_t defs_capacity;
@@ -76,8 +77,8 @@ struct DstAssembler {
  * prefix tree. */
 static const DstInstructionDef dst_ops[] = {
     {"add", DOP_ADD},
-    {"addim", DOP_ADD_IMMEDIATE},
     {"addi", DOP_ADD_INTEGER},
+    {"addim", DOP_ADD_IMMEDIATE},
     {"addr", DOP_ADD_REAL},
     {"band", DOP_BAND},
     {"bnot", DOP_BNOT},
@@ -88,8 +89,8 @@ static const DstInstructionDef dst_ops[] = {
     {"cmp", DOP_COMPARE},
     {"debug", DOP_DEBUG},
     {"div", DOP_DIVIDE},
-    {"divim", DOP_DIVIDE_IMMEDIATE},
     {"divi", DOP_DIVIDE_INTEGER},
+    {"divim", DOP_DIVIDE_IMMEDIATE},
     {"divr", DOP_DIVIDE_REAL},
     {"eq", DOP_EQUALS},
     {"err", DOP_ERROR},
@@ -99,25 +100,25 @@ static const DstInstructionDef dst_ops[] = {
     {"jmp", DOP_JUMP},
     {"jmpi", DOP_JUMP_IF},
     {"jmpn", DOP_JUMP_IF_NOT},
+    {"ldc", DOP_LOAD_CONSTANT},
+    {"ldf", DOP_LOAD_FALSE},
+    {"ldi", DOP_LOAD_INTEGER},
+    {"ldn", DOP_LOAD_NIL},
+    {"lds", DOP_LOAD_SELF},
+    {"ldt", DOP_LOAD_TRUE},
+    {"ldu", DOP_LOAD_UPVALUE},
     {"lt", DOP_LESS_THAN},
-    {"lc", DOP_LOAD_CONSTANT},
-    {"lf", DOP_LOAD_FALSE},
-    {"li", DOP_LOAD_INTEGER},
-    {"ln", DOP_LOAD_NIL},
-    {"ls", DOP_LOAD_SELF},
-    {"lt", DOP_LOAD_TRUE},
-    {"lu", DOP_LOAD_UPVALUE},
     {"movf", DOP_MOVE_FAR},
     {"movn", DOP_MOVE_NEAR},
     {"mul", DOP_MULTIPLY},
-    {"mulim", DOP_MULTIPLY_IMMEDIATE},
     {"muli", DOP_MULTIPLY_INTEGER},
+    {"mulim", DOP_MULTIPLY_IMMEDIATE},
     {"mulr", DOP_MULTIPLY_REAL},
     {"noop", DOP_NOOP},
     {"push", DOP_PUSH},
-    {"pusha", DOP_PUSH_ARRAY},
     {"push2", DOP_PUSH_2},
     {"push3", DOP_PUSH_3},
+    {"pusha", DOP_PUSH_ARRAY},
     {"put", DOP_PUT},
     {"puti", DOP_PUT_INDEX},
     {"res", DOP_RESUME},
@@ -168,7 +169,7 @@ static void dst_asm_deinit(DstAssembler *a) {
 
 /* Throw some kind of assembly error */
 static void dst_asm_error(DstAssembler *a, const char *message) {
-    a->errmessage = dst_cstring(message);
+    a->errmessage = dst_formatc("%s, instruction %d", message, a->errindex);
     longjmp(a->on_error, 1);
 }
 #define dst_asm_assert(a, c, m) do { if (!(c)) dst_asm_error((a), (m)); } while (0)
@@ -469,6 +470,7 @@ static DstAssembleResult dst_asm1(DstAssembler *parent, Dst source, int flags) {
     a.def = def;
     a.parent = parent;
     a.errmessage = NULL;
+    a.errindex = 0;
     a.environments_capacity = 0;
     a.bytecode_count = 0;
     a.defs_capacity = 0;
@@ -613,6 +615,7 @@ static DstAssembleResult dst_asm1(DstAssembler *parent, Dst source, int flags) {
             } else if (dst_checktype(instr, DST_TUPLE)) {
                 blength++;
             } else {
+                a.errindex = i;
                 dst_asm_error(&a, "expected assembly instruction");
             }
         }
@@ -631,6 +634,7 @@ static DstAssembleResult dst_asm1(DstAssembler *parent, Dst source, int flags) {
                 uint32_t op;
                 const DstInstructionDef *idef;
                 const Dst *t;
+                a.errindex = i;
                 dst_asm_assert(&a, dst_checktype(instr, DST_TUPLE), "expected tuple");
                 t = dst_unwrap_tuple(instr);
                 if (dst_tuple_length(t) == 0) {
@@ -653,6 +657,7 @@ static DstAssembleResult dst_asm1(DstAssembler *parent, Dst source, int flags) {
     } else {
         dst_asm_error(&a, "bytecode expected");
     }
+    a.errindex = -1;
     
     /* Check for source mapping */
     x = dst_get(s, dst_csymbolv("sourcemap"));
diff --git a/src/compiler/boot.dst b/src/compiler/boot.dst
index d053e791..19740463 100644
--- a/src/compiler/boot.dst
+++ b/src/compiler/boot.dst
@@ -335,15 +335,13 @@ If no match is found, returns nil"
   (foreach s (fn [x] (put tab x true)))
   (keys tab))
 
-(defn make-env [parent]
+(defn make-env [parent safe]
  (def parent (if parent parent _env))
  (def newenv (setproto @{} parent))
- (put newenv '_env @{'value newenv})
+ (if (not safe)
+   (put newenv '_env @{'value newenv}))
  newenv)
 
-# Remove the reference to the default _env
-(put _env '_env nil)
-
 (def run-context 
 "Run a context. This evaluates expressions of dst in an environment,
 and is encapsulates the parsing, compilation, and evaluation of dst.
diff --git a/src/mainclient/init.dst b/src/mainclient/init.dst
index 6e0dab5f..d43957a3 100644
--- a/src/mainclient/init.dst
+++ b/src/mainclient/init.dst
@@ -28,7 +28,7 @@
   (dohandler (string-slice arg 1 2))
   (do
    (varset! no-file false)
-   (require arg))))
+   (import arg))))
 
 (when (or should-repl no-file) 
  (print (string "Dst " VERSION "  Copyright (C) 2017-2018 Calvin Rose"))