diff --git a/scripts/update_asm_instructions.py b/scripts/update_asm_instructions.py
index 2eef0e4..4d9cfa7 100755
--- a/scripts/update_asm_instructions.py
+++ b/scripts/update_asm_instructions.py
@@ -36,6 +36,12 @@ re_lookup = re.compile(
     r"(/\* @AUTOGEN_LOOKUP_BLOCK_START \*/\n*)(.*?)"
     r"(\n*/\* @AUTOGEN_LOOKUP_BLOCK_END \*/)", re.S)
 
+def _rindex(L, val):
+    """
+    Return the index of the last occurence of val in L.
+    """
+    return len(L) - L[::-1].index(val) - 1
+
 def _atoi(value):
     """
     Try to convert a string to an integer, supporting decimal and hexadecimal.
@@ -57,6 +63,22 @@ def _call_args(call, func):
     """
     return call[len(func) + 1:-1].strip()
 
+def _parse_step_args(call, func):
+    """
+    Parse arguments to a step function (e.g. reg() or cond()).
+    """
+    args = _call_args(call, func)
+    if " " in args:
+        return map(_atoi, args.split(" "))
+    else:
+        return _atoi(args), 1
+
+class ASMInstError(Exception):
+    """
+    Base class for all errors while trying to generate the instructions file.
+    """
+
+
 class Instruction(object):
     """
     Represent a single ASM instruction mnemonic.
@@ -72,13 +94,32 @@ class Instruction(object):
     PSEUDO_TYPES = {
         "indirect_hl_or_indexed": ["AT_INDIRECT", "AT_INDEXED"]
     }
+    REGISTER_OFFSETS = {
+        "a": 7,
+        "b": 0,
+        "c": 1,
+        "d": 2,
+        "e": 3,
+        "h": 4,
+        "ixh": 4,
+        "iyh": 4,
+        "l": 5,
+        "ixl": 5,
+        "iyl": 5,
+
+        "bc": 0,
+        "de": 1,
+        "hl": 2,
+        "ix": 2,
+        "iy": 2,
+        "sp": 3
+    }
+    CONDITION_ORDER = ["nz", "z", "nc", "c", "po", "pe", "p", "m"]
 
     def __init__(self, name, data):
         self._name = name
         self._data = data
-
         self._has_optional_args = False
-        self._step_state = {}
 
     def _get_arg_parse_mask(self, num):
         """
@@ -159,13 +200,13 @@ class Instruction(object):
             return "INST_INDIRECT({0}).type == AT_IMMEDIATE".format(num)
 
         err = "Unknown condition for indirect argument: {0}"
-        return RuntimeError(err.format(cond))
+        return ASMInstError(err.format(cond))
 
     def _build_indexed_check(self, num, cond):
         """
         Return an expression to check for a particular indexed value.
         """
-        raise RuntimeError("The indexed arg type does not support conditions")
+        raise ASMInstError("The indexed arg type does not support conditions")
 
     def _build_condition_check(self, num, cond):
         """
@@ -183,7 +224,7 @@ class Instruction(object):
             return "INST_PORT({0}).type == AT_IMMEDIATE".format(num)
 
         err = "Unknown condition for port argument: {0}"
-        return RuntimeError(err.format(cond))
+        return ASMInstError(err.format(cond))
 
     _SUBCASE_LOOKUP_TABLE = {
         "register": _build_register_check,
@@ -212,7 +253,7 @@ class Instruction(object):
                 merged = [choice for s in splits for choice in s]
                 if len(merged) != len(set(merged)):
                     msg = "Repeated conditions for {0}: {1}"
-                    raise RuntimeError(msg.format(typ, cond))
+                    raise ASMInstError(msg.format(typ, cond))
                 return merged
             if typ == "register":
                 if cond == "i":
@@ -228,32 +269,20 @@ class Instruction(object):
 
         if any(1 < len(cond) < num for cond in splits):
             msg = "Invalid condition permutations: {0}"
-            raise RuntimeError(msg.format(conds))
+            raise ASMInstError(msg.format(conds))
 
         choices = [cond * num if len(cond) == 1 else cond for cond in splits]
         return zip(*choices)
 
-    def _step(self, argdata):
-        """
-        Evaluate a step function call into a single byte.
-        """
-        args = _call_args(argdata, "step")
-        if " " in args:
-            base, stride = map(_atoi, args.split(" "))
-        else:
-            base, stride = _atoi(args), 1
-
-        if base not in self._step_state:
-            self._step_state[base] = 0
-
-        byte = base + self._step_state[base] * stride
-        self._step_state[base] += 1
-        return byte
-
     def _adapt_return(self, types, conds, ret):
         """
         Return a modified byte list to accomodate for prefixes and immediates.
         """
+        def handle_reg_func(call):
+            base, stride = _parse_step_args(call, "reg")
+            index = _rindex(types, "register")
+            return base + self.REGISTER_OFFSETS[conds[index]] * stride
+
         ret = ret[:]
         for i, byte in enumerate(ret):
             if not isinstance(byte, int):
@@ -268,7 +297,7 @@ class Instruction(object):
 
                 elif byte == "u16":
                     if i < len(ret) - 1:
-                        raise RuntimeError("U16 return byte must be last")
+                        raise ASMInstError("U16 return byte must be last")
                     try:
                         index = types.index("immediate")
                         imm = "INST_IMM({0})".format(index)
@@ -276,7 +305,7 @@ class Instruction(object):
                         indir = types.index("indirect")
                         if not conds[indir].startswith("imm"):
                             msg = "Passing non-immediate indirect as immediate"
-                            raise RuntimeError(msg)
+                            raise ASMInstError(msg)
                         imm = "INST_INDIRECT({0}).addr.imm".format(indir)
                     ret[i] = "INST_IMM_U16_B1({0})".format(imm)
                     ret.append("INST_IMM_U16_B2({0})".format(imm))
@@ -289,17 +318,23 @@ class Instruction(object):
                 elif _is_call(byte, "bit"):
                     index = types.index("immediate")
                     base = _call_args(byte, "bit")
-                    if _is_call(base, "step"):
-                        base = self._step(base)
+                    if _is_call(base, "reg"):
+                        base = handle_reg_func(base)
                     ret[i] = "0x{0:02X} + 8 * INST_IMM({1}).uval".format(
                         _atoi(base), index)
 
-                elif _is_call(byte, "step"):
-                    ret[i] = self._step(byte)
+                elif _is_call(byte, "reg"):
+                    ret[i] = handle_reg_func(byte)
+
+                elif _is_call(byte, "cond"):
+                    base, stride = _parse_step_args(byte, "cond")
+                    index = types.index("condition")
+                    offset = self.CONDITION_ORDER.index(conds[index])
+                    ret[i] = base + offset * stride
 
                 else:
                     msg = "Unsupported return byte: {0}"
-                    raise RuntimeError(msg.format(byte))
+                    raise ASMInstError(msg.format(byte))
 
         for i, cond in enumerate(conds):
             if types[i] == "register" and cond[0] == "i":
@@ -343,7 +378,7 @@ class Instruction(object):
 
             return indirect + indexed
 
-        raise RuntimeError("Unknown pseudo-type: {0}".format(pseudo))
+        raise ASMInstError("Unknown pseudo-type: {0}".format(pseudo))
 
     def _handle_case(self, case):
         """
@@ -361,9 +396,8 @@ class Instruction(object):
         cond = self._build_case_type_check(ctype)
         lines.append(TAB + "if ({0}) {{".format(cond))
 
-        self._step_state = {}
         subcases = [(perm, sub["return"]) for sub in case["cases"]
-                    for perm in self._iter_permutations(ctype, sub["cond"])]
+                    for perm in self._iter_permutations(ctype, sub["if"])]
         for cond, ret in subcases:
             check = self._build_subcase_check(ctype, cond)
             ret = self._adapt_return(ctype, cond, ret)
@@ -401,32 +435,32 @@ class Instruction(object):
             lines.append(TAB + "INST_ERROR(ARG_TYPE)")
         else:
             msg = "Missing return or case block for {0} instruction"
-            raise RuntimeError(msg.format(self._name))
+            raise ASMInstError(msg.format(self._name))
 
         contents = "\n".join(lines)
         return "INST_FUNC({0})\n{{\n{1}\n}}".format(self._name, contents)
 
 
-def build_inst_block(data):
+def _build_inst_block(data):
     """
     Return the instruction parser block, given instruction data.
     """
     return "\n\n".join(
         Instruction(k, v).render() for k, v in sorted(data.items()))
 
-def build_lookup_block(data):
+def _build_lookup_block(data):
     """
     Return the instruction lookup block, given instruction data.
     """
     macro = TAB + "HANDLE({0})"
     return "\n".join(macro.format(inst) for inst in sorted(data.keys()))
 
-def process(template, data):
+def _process(template, data):
     """
     Return C code generated from a source template and instruction data.
     """
-    inst_block = build_inst_block(data)
-    lookup_block = build_lookup_block(data)
+    inst_block = _build_inst_block(data)
+    lookup_block = _build_lookup_block(data)
     date = time.asctime(time.gmtime())
 
     result = re_date.sub(r"\1{0} UTC".format(date), template)
@@ -444,7 +478,7 @@ def main():
         template = fp.read().decode(ENCODING)
 
     data = yaml.load(text)
-    result = process(template, data)
+    result = _process(template, data)
 
     with open(DEST, "w") as fp:
         fp.write(result.encode(ENCODING))
diff --git a/src/assembler/instructions.inc.c b/src/assembler/instructions.inc.c
index 8c8e3f1..303691d 100644
--- a/src/assembler/instructions.inc.c
+++ b/src/assembler/instructions.inc.c
@@ -7,7 +7,7 @@
     `make` should trigger a rebuild when it is modified; if not, use:
     `python scripts/update_asm_instructions.py`.
 
-    @AUTOGEN_DATE Thu May 21 23:52:57 2015 UTC
+    @AUTOGEN_DATE Fri May 22 00:38:38 2015 UTC
 */
 
 /* @AUTOGEN_INST_BLOCK_START */
diff --git a/src/assembler/instructions.yml b/src/assembler/instructions.yml
index 1480004..309b180 100644
--- a/src/assembler/instructions.yml
+++ b/src/assembler/instructions.yml
@@ -15,23 +15,23 @@ adc:
     cases:
         - type: [register, register]
           cases:
-            - cond:   [a, a]
+            - if:     [a, a]
               return: [0x8F]
-            - cond:   [a, b|c|d|e]
-              return: [step(0x88)]
-            - cond:   [a, h|ih]
+            - if:     [a, b|c|d|e]
+              return: [reg(0x88)]
+            - if:     [a, h|ih]
               return: [0x8C]
-            - cond:   [a, l|il]
+            - if:     [a, l|il]
               return: [0x8D]
-            - cond:   [hl, bc|de|hl|sp]
-              return: [0xED, step(0x4A 0x10)]
+            - if:     [hl, bc|de|hl|sp]
+              return: [0xED, reg(0x4A 0x10)]
         - type: [register, immediate]
           cases:
-            - cond:   [a, u8]
+            - if:     [a, u8]
               return: [0xCE, u8]
         - type: [register, indirect_hl_or_indexed]
           cases:
-            - cond:   [a, _]
+            - if:     [a, _]
               return: [0x8E]
 
 add:
@@ -39,29 +39,29 @@ add:
     cases:
         - type: [register, register]
           cases:
-            - cond:   [a, a]
+            - if:     [a, a]
               return: [0x87]
-            - cond:   [a, b|c|d|e]
-              return: [step(0x80)]
-            - cond:   [a, h|ih]
+            - if:     [a, b|c|d|e]
+              return: [reg(0x80)]
+            - if:     [a, h|ih]
               return: [0x84]
-            - cond:   [a, l|il]
+            - if:     [a, l|il]
               return: [0x85]
-            - cond:   [hl|i, bc]
+            - if:     [hl|i, bc]
               return: [0x09]
-            - cond:   [hl|i, de]
+            - if:     [hl|i, de]
               return: [0x19]
-            - cond:   [hl|i, hl|i]
+            - if:     [hl|i, hl|i]
               return: [0x29]
-            - cond:   [hl|i, sp]
+            - if:     [hl|i, sp]
               return: [0x39]
         - type: [register, immediate]
           cases:
-            - cond:   [a, u8]
+            - if:     [a, u8]
               return: [0xC6, u8]
         - type: [register, indirect_hl_or_indexed]
           cases:
-            - cond:   [a, _]
+            - if:     [a, _]
               return: [0x86]
 
 and:
@@ -69,21 +69,21 @@ and:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xA7]
-            - cond:   [b|c|d|e]
-              return: [step(0xA0)]
-            - cond:   [h|ih]
+            - if:     [b|c|d|e]
+              return: [reg(0xA0)]
+            - if:     [h|ih]
               return: [0xA4]
-            - cond:   [l|il]
+            - if:     [l|il]
               return: [0xA5]
         - type: [immediate]
           cases:
-            - cond:   [u8]
+            - if:     [u8]
               return: [0xE6, u8]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xA6]
 
 bit:
@@ -91,13 +91,13 @@ bit:
     cases:
         - type: [immediate, register]
           cases:
-            - cond:   [bit, a]
+            - if:     [bit, a]
               return: [0xCB, bit(0x47)]
-            - cond:   [bit, b|c|d|e|h|l]
-              return: [0xCB, bit(step(0x40))]
+            - if:     [bit, b|c|d|e|h|l]
+              return: [0xCB, bit(reg(0x40))]
         - type: [immediate, indirect_hl_or_indexed]
           cases:
-            - cond:   [bit, _]
+            - if:     [bit, _]
               return: [0xCB, bit(0x46)]
 
 call:
@@ -105,12 +105,12 @@ call:
     cases:
         - type: [immediate]
           cases:
-            - cond:   [u16]
+            - if:     [u16]
               return: [0xCD, u16]
         - type: [condition, immediate]
           cases:
-            - cond:   [nz|z|nc|c|po|pe|p|m, u16]
-              return: [step(0xC4 0x08), u16]
+            - if:     [nz|z|nc|c|po|pe|p|m, u16]
+              return: [cond(0xC4 0x08), u16]
 
 ccf:
     args: no
@@ -121,21 +121,21 @@ cp:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xBF]
-            - cond:   [b|c|d|e]
-              return: [step(0xB8)]
-            - cond:   [h|ih]
+            - if:     [b|c|d|e]
+              return: [reg(0xB8)]
+            - if:     [h|ih]
               return: [0xBC]
-            - cond:   [l|il]
+            - if:     [l|il]
               return: [0xBD]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xBE]
         - type: [immediate]
           cases:
-            - cond:   [u8]
+            - if:     [u8]
               return: [0xFE, u8]
 
 cpd:
@@ -167,25 +167,25 @@ dec:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0x3D]
-            - cond:   [b|c|d|e]
-              return: [step(0x05 0x08)]
-            - cond:   [h|ih]
+            - if:     [b|c|d|e]
+              return: [reg(0x05 0x08)]
+            - if:     [h|ih]
               return: [0x25]
-            - cond:   [l|il]
+            - if:     [l|il]
               return: [0x2D]
-            - cond:   [bc]
+            - if:     [bc]
               return: [0x0B]
-            - cond:   [de]
+            - if:     [de]
               return: [0x1B]
-            - cond:   [hl|i]
+            - if:     [hl|i]
               return: [0x2B]
-            - cond:   [sp]
+            - if:     [sp]
               return: [0x3B]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0x35]
 
 di:
@@ -197,7 +197,7 @@ djnz:
     cases:
         - type: [immediate]
           cases:
-            - cond:   [rel]
+            - if:     [rel]
               return: [0x10, rel]
 
 ei:
@@ -209,13 +209,13 @@ ex:
     cases:
         - type: [register, register]
           cases:
-            - cond:   [af, af_]
+            - if:     [af, af_]
               return: [0x08]
-            - cond:   [de, hl]
+            - if:     [de, hl]
               return: [0xEB]
         - type: [indirect, register]
           cases:
-            - cond:   [reg.sp, hl|i]
+            - if:     [reg.sp, hl|i]
               return: [0xE3]
 
 exx:
@@ -231,11 +231,11 @@ im:
     cases:
         - type: [immediate]
           cases:
-            - cond:   [im.0]
+            - if:     [im.0]
               return: [0xED, 0x46]
-            - cond:   [im.1]
+            - if:     [im.1]
               return: [0xED, 0x56]
-            - cond:   [im.2]
+            - if:     [im.2]
               return: [0xED, 0x5E]
 
 in:
@@ -243,15 +243,15 @@ in:
     cases:
         - type: [register, port]
           cases:
-            - cond:   [a, imm]
+            - if:     [a, imm]
               return: [0xDB, u8]
-            - cond:   [a, reg.c]
+            - if:     [a, reg.c]
               return: [0xED, 0x78]
-            - cond:   [b|c|d|e|h|l, reg.c]
-              return: [0xED, step(0x40 0x08)]
+            - if:     [b|c|d|e|h|l, reg.c]
+              return: [0xED, reg(0x40 0x08)]
         - type: [port]
           cases:
-            - cond:   [reg.c]
+            - if:     [reg.c]
               return: [0xED, 0x70]
 
 inc:
@@ -259,25 +259,25 @@ inc:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0x3C]
-            - cond:   [b|c|d|e]
-              return: [step(0x04 0x08)]
-            - cond:   [h|ih]
+            - if:     [b|c|d|e]
+              return: [reg(0x04 0x08)]
+            - if:     [h|ih]
               return: [0x24]
-            - cond:   [l|il]
+            - if:     [l|il]
               return: [0x2C]
-            - cond:   [bc]
+            - if:     [bc]
               return: [0x03]
-            - cond:   [de]
+            - if:     [de]
               return: [0x13]
-            - cond:   [hl|i]
+            - if:     [hl|i]
               return: [0x23]
-            - cond:   [sp]
+            - if:     [sp]
               return: [0x33]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0x34]
 
 ind:
@@ -301,15 +301,15 @@ jp:
     cases:
         - type: [immediate]
           cases:
-            - cond:   [u16]
+            - if:     [u16]
               return: [0xC3, u16]
         - type: [condition, immediate]
           cases:
-            - cond:   [nz|z|nc|c|po|pe|p|m, u16]
-              return: [step(0xC2 0x08), u16]
+            - if:     [nz|z|nc|c|po|pe|p|m, u16]
+              return: [cond(0xC2 0x08), u16]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xE9]
 
 jr:
@@ -317,161 +317,161 @@ jr:
     cases:
         - type: [immediate]
           cases:
-            - cond:   [rel]
+            - if:     [rel]
               return: [0x18, rel]
         - type: [condition, immediate]
           cases:
-            - cond:   [nz|z|nc|c, rel]
-              return: [step(0x20 0x08), rel]
+            - if:     [nz|z|nc|c, rel]
+              return: [cond(0x20 0x08), rel]
 
 ld:
     args: yes
     cases:
         - type: [register, register]
           cases:
-            - cond:   [a, a]
+            - if:     [a, a]
               return: [0x7F]
-            - cond:   [a, b|c|d|e]
-              return: [step(0x78)]
-            - cond:   [a, h|ih]
+            - if:     [a, b|c|d|e]
+              return: [reg(0x78)]
+            - if:     [a, h|ih]
               return: [0x7C]
-            - cond:   [a, l|il]
+            - if:     [a, l|il]
               return: [0x7D]
-            - cond:   [b, a]
+            - if:     [b, a]
               return: [0x47]
-            - cond:   [b, b|c|d|e]
-              return: [step(0x40)]
-            - cond:   [b, h|ih]
+            - if:     [b, b|c|d|e]
+              return: [reg(0x40)]
+            - if:     [b, h|ih]
               return: [0x44]
-            - cond:   [b, l|il]
+            - if:     [b, l|il]
               return: [0x45]
-            - cond:   [c, a]
+            - if:     [c, a]
               return: [0x4F]
-            - cond:   [c, b|c|d|e]
-              return: [step(0x48)]
-            - cond:   [c, h|ih]
+            - if:     [c, b|c|d|e]
+              return: [reg(0x48)]
+            - if:     [c, h|ih]
               return: [0x4C]
-            - cond:   [c, l|il]
+            - if:     [c, l|il]
               return: [0x4D]
-            - cond:   [d, a]
+            - if:     [d, a]
               return: [0x57]
-            - cond:   [d, b|c|d|e]
-              return: [step(0x50)]
-            - cond:   [d, h|ih]
+            - if:     [d, b|c|d|e]
+              return: [reg(0x50)]
+            - if:     [d, h|ih]
               return: [0x54]
-            - cond:   [d, l|il]
+            - if:     [d, l|il]
               return: [0x55]
-            - cond:   [e, a]
+            - if:     [e, a]
               return: [0x5F]
-            - cond:   [e, b|c|d|e]
-              return: [step(0x58)]
-            - cond:   [e, h|ih]
+            - if:     [e, b|c|d|e]
+              return: [reg(0x58)]
+            - if:     [e, h|ih]
               return: [0x5C]
-            - cond:   [e, l|il]
+            - if:     [e, l|il]
               return: [0x5D]
-            - cond:   [h|ih, a]
+            - if:     [h|ih, a]
               return: [0x67]
-            - cond:   [h|ih, b]
+            - if:     [h|ih, b]
               return: [0x60]
-            - cond:   [h|ih, c]
+            - if:     [h|ih, c]
               return: [0x61]
-            - cond:   [h|ih, d]
+            - if:     [h|ih, d]
               return: [0x62]
-            - cond:   [h|ih, e]
+            - if:     [h|ih, e]
               return: [0x63]
-            - cond:   [h|ih, h|ih]
+            - if:     [h|ih, h|ih]
               return: [0x64]
-            - cond:   [h|ih, l|il]
+            - if:     [h|ih, l|il]
               return: [0x65]
-            - cond:   [l|il, a]
+            - if:     [l|il, a]
               return: [0x6F]
-            - cond:   [l|il, b]
+            - if:     [l|il, b]
               return: [0x68]
-            - cond:   [l|il, c]
+            - if:     [l|il, c]
               return: [0x69]
-            - cond:   [l|il, d]
+            - if:     [l|il, d]
               return: [0x6A]
-            - cond:   [l|il, e]
+            - if:     [l|il, e]
               return: [0x6B]
-            - cond:   [l|il, h|ih]
+            - if:     [l|il, h|ih]
               return: [0x6C]
-            - cond:   [l|il, l|il]
+            - if:     [l|il, l|il]
               return: [0x6D]
-            - cond:   [a, i]
+            - if:     [a, i]
               return: [0xED, 0x57]
-            - cond:   [i, a]
+            - if:     [i, a]
               return: [0xED, 0x47]
-            - cond:   [a, r]
+            - if:     [a, r]
               return: [0xED, 0x5F]
-            - cond:   [r, a]
+            - if:     [r, a]
               return: [0xED, 0x4F]
-            - cond:   [sp, hl|i]
+            - if:     [sp, hl|i]
               return: [0xF9]
         - type: [register, immediate]
           cases:
-            - cond:   [a, u8]
+            - if:     [a, u8]
               return: [0x3E, u8]
-            - cond:   [b|c|d|e, u8]
-              return: [step(0x06 0x08), u8]
-            - cond:   [h|ih, u8]
+            - if:     [b|c|d|e, u8]
+              return: [reg(0x06 0x08), u8]
+            - if:     [h|ih, u8]
               return: [0x26, u8]
-            - cond:   [l|il, u8]
+            - if:     [l|il, u8]
               return: [0x2E, u8]
-            - cond:   [bc, u16]
+            - if:     [bc, u16]
               return: [0x01, u16]
-            - cond:   [de, u16]
+            - if:     [de, u16]
               return: [0x11, u16]
-            - cond:   [hl|i, u16]
+            - if:     [hl|i, u16]
               return: [0x21, u16]
-            - cond:   [sp, u16]
+            - if:     [sp, u16]
               return: [0x31, u16]
         - type: [register, indirect_hl_or_indexed]
           cases:
-            - cond:   [a, _]
+            - if:     [a, _]
               return: [0x7E]
-            - cond:   [b|c|d|e|h|l, _]
-              return: [step(0x46 0x08)]
+            - if:     [b|c|d|e|h|l, _]
+              return: [reg(0x46 0x08)]
         - type: [register, indirect]
           cases:
-            - cond:   [a, reg.bc]
+            - if:     [a, reg.bc]
               return: [0x0A]
-            - cond:   [a, reg.de]
+            - if:     [a, reg.de]
               return: [0x1A]
-            - cond:   [hl|i, imm]
+            - if:     [hl|i, imm]
               return: [0x2A, u16]
-            - cond:   [a, imm]
+            - if:     [a, imm]
               return: [0x3A, u16]
-            - cond:   [bc, imm]
+            - if:     [bc, imm]
               return: [0xED, 0x4B, u16]
-            - cond:   [de, imm]
+            - if:     [de, imm]
               return: [0xED, 0x5B, u16]
-            - cond:   [sp, imm]
+            - if:     [sp, imm]
               return: [0xED, 0x7B, u16]
         - type: [indirect_hl_or_indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0x77]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [step(0x70)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [reg(0x70)]
         - type: [indirect_hl_or_indexed, immediate]
           cases:
-            - cond:   [_, u8]
+            - if:     [_, u8]
               return: [0x36, u8]
         - type: [indirect, register]
           cases:
-            - cond:   [reg.bc, a]
+            - if:     [reg.bc, a]
               return: [0x02]
-            - cond:   [reg.de, a]
+            - if:     [reg.de, a]
               return: [0x12]
-            - cond:   [imm, hl|i]
+            - if:     [imm, hl|i]
               return: [0x22, u16]
-            - cond:   [imm, a]
+            - if:     [imm, a]
               return: [0x32, u16]
-            - cond:   [imm, bc]
+            - if:     [imm, bc]
               return: [0xED, 0x43, u16]
-            - cond:   [imm, de]
+            - if:     [imm, de]
               return: [0xED, 0x53, u16]
-            - cond:   [imm, sp]
+            - if:     [imm, sp]
               return: [0xED, 0x73, u16]
 
 ldd:
@@ -503,21 +503,21 @@ or:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xB7]
-            - cond:   [b|c|d|e]
-              return: [step(0xB0)]
-            - cond:   [h|ih]
+            - if:     [b|c|d|e]
+              return: [reg(0xB0)]
+            - if:     [h|ih]
               return: [0xB4]
-            - cond:   [l|il]
+            - if:     [l|il]
               return: [0xB5]
         - type: [immediate]
           cases:
-            - cond:   [u8]
+            - if:     [u8]
               return: [0xF6, u8]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xB6]
 
 otdr:
@@ -533,15 +533,15 @@ out:
     cases:
         - type: [port, register]
           cases:
-            - cond:   [imm, a]
+            - if:     [imm, a]
               return: [0xD3, u8]
-            - cond:   [reg.c, a]
+            - if:     [reg.c, a]
               return: [0xED, 0x79]
-            - cond:   [reg.c, b|c|d|e|h|l]
-              return: [0xED, step(0x41 0x08)]
+            - if:     [reg.c, b|c|d|e|h|l]
+              return: [0xED, reg(0x41 0x08)]
         - type: [port, immediate]
           cases:
-            - cond:   [reg.c, u8.0]
+            - if:     [reg.c, u8.0]
               return: [0xED, 0x71]
 
 outd:
@@ -557,13 +557,13 @@ pop:
     cases:
         - type: [register]
           cases:
-            - cond:   [bc]
+            - if:     [bc]
               return: [0xC1]
-            - cond:   [de]
+            - if:     [de]
               return: [0xD1]
-            - cond:   [hl|i]
+            - if:     [hl|i]
               return: [0xE1]
-            - cond:   [af]
+            - if:     [af]
               return: [0xF1]
 
 push:
@@ -571,13 +571,13 @@ push:
     cases:
         - type: [register]
           cases:
-            - cond:   [bc]
+            - if:     [bc]
               return: [0xC5]
-            - cond:   [de]
+            - if:     [de]
               return: [0xD5]
-            - cond:   [hl|i]
+            - if:     [hl|i]
               return: [0xE5]
-            - cond:   [af]
+            - if:     [af]
               return: [0xF5]
 
 res:
@@ -585,20 +585,20 @@ res:
     cases:
         - type: [immediate, register]
           cases:
-            - cond:   [bit, a]
+            - if:     [bit, a]
               return: [0xCB, bit(0x87)]
-            - cond:   [bit, b|c|d|e|h|l]
-              return: [0xCB, bit(step(0x80))]
+            - if:     [bit, b|c|d|e|h|l]
+              return: [0xCB, bit(reg(0x80))]
         - type: [immediate, indirect_hl_or_indexed]
           cases:
-            - cond:   [bit, _]
+            - if:     [bit, _]
               return: [0xCB, bit(0x86)]
         - type: [immediate, indexed, register]
           cases:
-            - cond:   [bit, _, a]
+            - if:     [bit, _, a]
               return: [0xCB, bit(0x87)]
-            - cond:   [bit, _, b|c|d|e|h|l]
-              return: [0xCB, bit(step(0x80))]
+            - if:     [bit, _, b|c|d|e|h|l]
+              return: [0xCB, bit(reg(0x80))]
 
 ret:
     args: yes
@@ -607,8 +607,8 @@ ret:
           return: [0xC9]
         - type: [condition]
           cases:
-            - cond:   [nz|z|nc|c|po|pe|p|m]
-              return: [step(0xC0 0x08)]
+            - if:     [nz|z|nc|c|po|pe|p|m]
+              return: [cond(0xC0 0x08)]
 
 reti:
     args: no
@@ -623,20 +623,20 @@ rl:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xCB, 0x17]
-            - cond:   [b|c|d|e|h|l]
-              return: [0xCB, step(0x10)]
+            - if:     [b|c|d|e|h|l]
+              return: [0xCB, reg(0x10)]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xCB, 0x16]
         - type: [indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0xCB, 0x17]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [0xCB, step(0x10)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [0xCB, reg(0x10)]
 
 rla:
     args: no
@@ -647,20 +647,20 @@ rlc:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xCB, 0x07]
-            - cond:   [b|c|d|e|h|l]
-              return: [0xCB, step(0x00)]
+            - if:     [b|c|d|e|h|l]
+              return: [0xCB, reg(0x00)]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xCB, 0x06]
         - type: [indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0xCB, 0x07]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [0xCB, step(0x00)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [0xCB, reg(0x00)]
 
 rlca:
     args: no
@@ -675,20 +675,20 @@ rr:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xCB, 0x1F]
-            - cond:   [b|c|d|e|h|l]
-              return: [0xCB, step(0x18)]
+            - if:     [b|c|d|e|h|l]
+              return: [0xCB, reg(0x18)]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xCB, 0x1E]
         - type: [indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0xCB, 0x1F]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [0xCB, step(0x18)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [0xCB, reg(0x18)]
 
 rra:
     args: no
@@ -699,20 +699,20 @@ rrc:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xCB, 0x0F]
-            - cond:   [b|c|d|e|h|l]
-              return: [0xCB, step(0x08)]
+            - if:     [b|c|d|e|h|l]
+              return: [0xCB, reg(0x08)]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xCB, 0x0E]
         - type: [indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0xCB, 0x0F]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [0xCB, step(0x08)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [0xCB, reg(0x08)]
 
 rrca:
     args: no
@@ -727,21 +727,21 @@ rst:
     cases:
         - type: [immediate]
           cases:
-            - cond:   [rst.0x00]
+            - if:     [rst.0x00]
               return: [0xC7]
-            - cond:   [rst.0x08]
+            - if:     [rst.0x08]
               return: [0xCF]
-            - cond:   [rst.0x10]
+            - if:     [rst.0x10]
               return: [0xD7]
-            - cond:   [rst.0x18]
+            - if:     [rst.0x18]
               return: [0xDF]
-            - cond:   [rst.0x20]
+            - if:     [rst.0x20]
               return: [0xE7]
-            - cond:   [rst.0x28]
+            - if:     [rst.0x28]
               return: [0xEF]
-            - cond:   [rst.0x30]
+            - if:     [rst.0x30]
               return: [0xF7]
-            - cond:   [rst.0x38]
+            - if:     [rst.0x38]
               return: [0xFF]
 
 sbc:
@@ -749,23 +749,23 @@ sbc:
     cases:
         - type: [register, register]
           cases:
-            - cond:   [a, a]
+            - if:     [a, a]
               return: [0x9F]
-            - cond:   [a, b|c|d|e]
-              return: [step(0x98)]
-            - cond:   [a, h|ih]
+            - if:     [a, b|c|d|e]
+              return: [reg(0x98)]
+            - if:     [a, h|ih]
               return: [0x9C]
-            - cond:   [a, l|il]
+            - if:     [a, l|il]
               return: [0x9D]
-            - cond:   [hl, bc|de|hl|sp]
-              return: [0xED, step(0x42 0x10)]
+            - if:     [hl, bc|de|hl|sp]
+              return: [0xED, reg(0x42 0x10)]
         - type: [register, immediate]
           cases:
-            - cond:   [a, u8]
+            - if:     [a, u8]
               return: [0xDE, u8]
         - type: [register, indirect_hl_or_indexed]
           cases:
-            - cond:   [a, _]
+            - if:     [a, _]
               return: [0x9E]
 
 scf:
@@ -777,60 +777,60 @@ set:
     cases:
         - type: [immediate, register]
           cases:
-            - cond:   [bit, a]
+            - if:     [bit, a]
               return: [0xCB, bit(0xC7)]
-            - cond:   [bit, b|c|d|e|h|l]
-              return: [0xCB, bit(step(0xC0))]
+            - if:     [bit, b|c|d|e|h|l]
+              return: [0xCB, bit(reg(0xC0))]
         - type: [immediate, indirect_hl_or_indexed]
           cases:
-            - cond:   [bit, _]
+            - if:     [bit, _]
               return: [0xCB, bit(0xC6)]
         - type: [immediate, indexed, register]
           cases:
-            - cond:   [bit, _, a]
+            - if:     [bit, _, a]
               return: [0xCB, bit(0xC7)]
-            - cond:   [bit, _, b|c|d|e|h|l]
-              return: [0xCB, bit(step(0xC0))]
+            - if:     [bit, _, b|c|d|e|h|l]
+              return: [0xCB, bit(reg(0xC0))]
 
 sl1: &sl1
     args: yes
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xCB, 0x37]
-            - cond:   [b|c|d|e|h|l]
-              return: [0xCB, step(0x30)]
+            - if:     [b|c|d|e|h|l]
+              return: [0xCB, reg(0x30)]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xCB, 0x36]
         - type: [indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0xCB, 0x37]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [0xCB, step(0x30)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [0xCB, reg(0x30)]
 
 sla:
     args: yes
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xCB, 0x27]
-            - cond:   [b|c|d|e|h|l]
-              return: [0xCB, step(0x20)]
+            - if:     [b|c|d|e|h|l]
+              return: [0xCB, reg(0x20)]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xCB, 0x26]
         - type: [indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0xCB, 0x27]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [0xCB, step(0x20)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [0xCB, reg(0x20)]
 
 sll: *sl1
 
@@ -841,61 +841,61 @@ sra:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xCB, 0x2F]
-            - cond:   [b|c|d|e|h|l]
-              return: [0xCB, step(0x28)]
+            - if:     [b|c|d|e|h|l]
+              return: [0xCB, reg(0x28)]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xCB, 0x2E]
         - type: [indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0xCB, 0x2F]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [0xCB, step(0x28)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [0xCB, reg(0x28)]
 
 srl:
     args: yes
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xCB, 0x3F]
-            - cond:   [b|c|d|e|h|l]
-              return: [0xCB, step(0x38)]
+            - if:     [b|c|d|e|h|l]
+              return: [0xCB, reg(0x38)]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xCB, 0x3E]
         - type: [indexed, register]
           cases:
-            - cond:   [_, a]
+            - if:     [_, a]
               return: [0xCB, 0x3F]
-            - cond:   [_, b|c|d|e|h|l]
-              return: [0xCB, step(0x38)]
+            - if:     [_, b|c|d|e|h|l]
+              return: [0xCB, reg(0x38)]
 
 sub:
     args: yes
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0x97]
-            - cond:   [b|c|d|e]
-              return: [step(0x90)]
-            - cond:   [h|ih]
+            - if:     [b|c|d|e]
+              return: [reg(0x90)]
+            - if:     [h|ih]
               return: [0x94]
-            - cond:   [l|il]
+            - if:     [l|il]
               return: [0x95]
         - type: [immediate]
           cases:
-            - cond:   [u8]
+            - if:     [u8]
               return: [0xD6, u8]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0x96]
 
 xor:
@@ -903,19 +903,19 @@ xor:
     cases:
         - type: [register]
           cases:
-            - cond:   [a]
+            - if:     [a]
               return: [0xAF]
-            - cond:   [b|c|d|e]
-              return: [step(0xA8)]
-            - cond:   [h|ih]
+            - if:     [b|c|d|e]
+              return: [reg(0xA8)]
+            - if:     [h|ih]
               return: [0xAC]
-            - cond:   [l|il]
+            - if:     [l|il]
               return: [0xAD]
         - type: [immediate]
           cases:
-            - cond:   [u8]
+            - if:     [u8]
               return: [0xEE, u8]
         - type: [indirect_hl_or_indexed]
           cases:
-            - cond:   [_]
+            - if:     [_]
               return: [0xAE]