doc/opcode.md: update according to
@@ -97,7 +97,7 @@ sign) of operands.
| `OP_ARYPUSH` | `BB` | `ary_push(R(a),R(a+1)..R(a+b))` |
| `OP_ARYDUP` | `B` | `R(a) = ary_dup(R(a))` |
| `OP_AREF` | `BBB` | `R(a) = R(b)[c]` |
-| `OP_ASET` | `BBB` | `R(a)[c] = R(b)` |
+| `OP_ASET` | `BBB` | `R(b)[c] = R(a)` |
| `OP_APOST` | `BBB` | `*R(a),R(a+1)..R(a+c) = R(a)[b..]` |
| `OP_INTERN` | `B` | `R(a) = intern(R(a))` |
| `OP_STRING` | `BB` | `R(a) = str_dup(Pool(b))` |
