diff --git a/src/holt59/aoc/2015/day23.py b/src/holt59/aoc/2015/day23.py
new file mode 100644
index 0000000..c93c253
--- /dev/null
+++ b/src/holt59/aoc/2015/day23.py
@@ -0,0 +1,107 @@
+import inspect
+from typing import Any, Callable, Final, Iterator, Mapping
+
+from ..base import BaseSolver
+
+
+class Instruction:
+    def __init__(self, fn: Callable[..., None]):
+        self._fn = fn
+
+        args = inspect.getfullargspec(fn)
+
+        self._argtypes = [args.annotations[arg] for arg in args.args[1:]]
+
+    def __call__(self, args: tuple[str, ...]):
+        self._fn(
+            *(argtype(arg) for arg, argtype in zip(args, self._argtypes, strict=True))
+        )
+
+
+class Machine:
+    def __init__(
+        self, instructions: list[str], registers: dict[str, int] = {"a": 0, "b": 1}
+    ):
+        self.instructions: Final = [
+            (part[0], tuple(arg.strip() for arg in " ".join(part[1:]).split(",")))
+            for instruction in instructions
+            if (part := instruction.split())
+        ]
+
+        self._fns = {
+            name: Instruction(getattr(self, name))
+            for name in ("hlf", "tpl", "inc", "jmp", "jie", "jio")
+        }
+
+        self._registers = registers.copy()
+        self._ip = 0
+
+    @property
+    def registers(self) -> Mapping[str, int]:
+        return self._registers
+
+    @property
+    def ip(self) -> int:
+        return self._ip
+
+    def reset(self, registers: dict[str, int] = {"a": 0, "b": 0}):
+        self._registers = registers.copy()
+        self._ip = 0
+
+    def hlf(self, register: str):
+        self._registers[register] //= 2
+        self._ip += 1
+
+    def tpl(self, register: str):
+        self._registers[register] *= 3
+        self._ip += 1
+
+    def inc(self, register: str):
+        self._registers[register] += 1
+        self._ip += 1
+
+    def jmp(self, offset: int):
+        self._ip += offset
+        assert 0 <= self._ip < len(self.instructions)
+
+    def jie(self, register: str, offset: int):
+        if self._registers[register] % 2 == 0:
+            self._ip += offset
+        else:
+            self._ip += 1
+
+    def jio(self, register: str, offset: int):
+        if self._registers[register] == 1:
+            self._ip += offset
+        else:
+            self._ip += 1
+
+    def _exec(self) -> bool:
+        # execute next instruction
+        if self._ip >= len(self.instructions):
+            return False
+
+        ins, args = self.instructions[self._ip]
+
+        if ins not in self._fns:
+            return False
+
+        self._fns[ins](args)
+        return True
+
+    def run(self):
+        while self._exec():
+            ...
+        return self.registers
+
+
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        machine = Machine(input.splitlines())
+
+        registers = machine.run()
+        yield registers["b"]
+
+        machine.reset({"a": 1, "b": 0})
+        registers = machine.run()
+        yield registers["b"]
diff --git a/src/holt59/aoc/inputs/holt59/2015/day23.txt b/src/holt59/aoc/inputs/holt59/2015/day23.txt
new file mode 100644
index 0000000..07b1c76
--- /dev/null
+++ b/src/holt59/aoc/inputs/holt59/2015/day23.txt
@@ -0,0 +1,49 @@
+jio a, +19
+inc a
+tpl a
+inc a
+tpl a
+inc a
+tpl a
+tpl a
+inc a
+inc a
+tpl a
+tpl a
+inc a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+jmp +23
+tpl a
+tpl a
+inc a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+inc a
+tpl a
+inc a
+tpl a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+tpl a
+inc a
+jio a, +8
+inc b
+jie a, +4
+tpl a
+inc a
+jmp +2
+hlf a
+jmp -7
diff --git a/src/holt59/aoc/inputs/tests/2015/day23.txt b/src/holt59/aoc/inputs/tests/2015/day23.txt
new file mode 100644
index 0000000..c55ca77
--- /dev/null
+++ b/src/holt59/aoc/inputs/tests/2015/day23.txt
@@ -0,0 +1,4 @@
+inc a
+jio a, +2
+tpl a
+inc a