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diff --git a/entries/jj/tm/tm.nim b/entries/jj/tm/tm.nim
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+# A simple Turing machine simulator implemented in Nim.
+
+import std/enumerate
+
+type Symbol = enum
+  `_`, `$`, `X`, `0`, `1`, `0*`, `1*`,
+  noop
+
+type Tape = seq[Symbol]
+
+type Direction = enum
+  L, R, S
+
+type State = enum
+  ca, cb, cc, cd, ce, cf, cg, ch, ci
+  sa, sb, sc, sd,
+  aa, ab, ac,
+  aaa, aab, aac, aad, aae, aaf,
+  aba, abb, abc, abd, abe, abf,
+  ba, bb, bc,
+  baa, bab, bac, bad, bae, baf,
+  bba, bbb, bbc, bbd, bbe, bbf,
+  za, zb, zc, zd
+
+type Transition = object
+  current_state: State
+  read_symbol: seq[Symbol]
+  next_state: State
+  write_symbol: Symbol
+  move_direction: Direction
+
+# convenience constructor
+func δ(a: State, b: seq[Symbol], c: State, d: Symbol, e: Direction): Transition =
+  return Transition(current_state: a, read_symbol: b, next_state: c, write_symbol: d, move_direction: e)
+
+# safe get for an infinite tape: pretty, right?
+func get(tape: var Tape, i: int): Symbol =
+  for j in tape.len .. i:
+    tape.add(`_`)
+  return tape[i]
+
+# safe set for an infinite tape
+func set(tape: var Tape, i: int, s: Symbol) =
+  for j in tape.len .. i:
+    tape.add(`_`)
+  tape[i] = s
+
+let turing_machine = @[
+  δ(ca, @[`_`], cb, `$`, R),
+  δ(cb, @[`_`], cc, `0`, R),
+  δ(cc, @[`_`], cd, `$`, R),
+  δ(cd, @[`_`], ce, `1*`, R),
+  δ(ce, @[`_`], cf, `$`, R),
+  δ(cf, @[`_`], cg, `1`, R),
+  δ(cg, @[`_`], ch, `$`, R),
+  δ(ch, @[`_`], sa, noop, S),
+
+  δ(sa, @[`_`, `X`], sa, noop, L),
+  δ(sa, @[`$`], sb, noop, L),
+  δ(sb, @[`0*`, `1*`], sb, noop, L),
+  δ(sb, @[`0`], sc, `0*`, R),
+  δ(sb, @[`1`], sc, `1*`, R),
+  δ(sb, @[`$`], sd, noop, R),
+  δ(sc, @[`$`, `X`, `0*`, `1*`], sc, noop, R),
+  δ(sc, @[`_`], sa, `X`, L),
+  δ(sd, @[`$`, `X`], sd, noop, R),
+  δ(sd, @[`0*`], sd, `0`, R),
+  δ(sd, @[`1*`], sd, `1`, R),
+  δ(sd, @[`_`], aa, noop, L),
+
+  δ(aa, @[`X`, `0`, `1`], aa, noop, L),
+  δ(aa, @[`$`], ab, noop, L),
+  δ(ab, @[`0*`, `1*`], ab, noop, L),
+  δ(ab, @[`0`], aaa, `0*`, L),
+  δ(ab, @[`1`], aba, `1*`, L),
+  δ(ab, @[`$`], ac, noop, R),
+  δ(ac, @[`$`, `X`, `0`, `1`, `0*`, `1*`], ac, noop, R),
+  δ(ac, @[`_`], sa, `$`, R),
+
+  δ(aaa, @[`0`, `1`], aaa, noop, L),
+  δ(aaa, @[`$`], aab, noop, L),
+  δ(aab, @[`0*`], aac, `0`, R),
+  δ(aac, @[`$`, `X`, `0`, `1`, `0*`, `1*`], aac, noop, R),
+  δ(aac, @[`_`], aad, noop, L),
+  δ(aad, @[`0`, `1`], aad, noop, L),
+  δ(aad, @[`X`], aa, `0`, L),
+  δ(aab, @[`1*`], aae, `1`, R),
+  δ(aae, @[`$`, `X`, `0`, `1`, `0*`, `1*`], aae, noop, R),
+  δ(aae, @[`_`], aaf, noop, L),
+  δ(aaf, @[`0`, `1`], aaf, noop, L),
+  δ(aaf, @[`X`], aa, `1`, L),
+  δ(aab, @[`0`, `1`], aab, noop, L),
+
+  δ(aba, @[`0`, `1`], aba, noop, L),
+  δ(aba, @[`$`], abb, noop, L),
+  δ(abb, @[`0*`], abc, `0`, R),
+  δ(abc, @[`$`, `X`, `0`, `1`, `0*`, `1*`], abc, noop, R),
+  δ(abc, @[`_`], abd, noop, L),
+  δ(abd, @[`0`, `1`], abd, noop, L),
+  δ(abd, @[`X`], aa, `1`, L),
+  δ(abb, @[`1*`], abe, `1`, R),
+  δ(abe, @[`$`, `X`, `0`, `1`, `0*`, `1*`], abe, noop, R),
+  δ(abe, @[`_`], abf, noop, L),
+  δ(abf, @[`0`, `1`], abf, noop, L),
+  δ(abf, @[`X`], ba, `0`, L),
+  δ(abb, @[`$`], abc, noop, R),
+  δ(abb, @[`0`, `1`], abb, noop, L),
+
+  δ(ba, @[`X`, `0`, `1`], ba, noop, L),
+  δ(ba, @[`$`], bb, noop, L),
+  δ(bb, @[`0*`, `1*`], bb, noop, L),
+  δ(bb, @[`0`], baa, `0*`, L),
+  δ(bb, @[`1`], bba, `1*`, L),
+  δ(bb, @[`$`], bc, noop, R),
+  δ(bc, @[`$`, `X`, `0`, `1`, `0*`, `1*`], bc, noop, R),
+  δ(bc, @[`_`], za, noop, L),
+
+  δ(baa, @[`0`, `1`], baa, noop, L),
+  δ(baa, @[`$`], bab, noop, L),
+  δ(bab, @[`0*`], bac, `0`, R),
+  δ(bac, @[`$`, `X`, `0`, `1`, `0*`, `1*`], bac, noop, R),
+  δ(bac, @[`_`], bad, noop, L),
+  δ(bad, @[`0`, `1`], bad, noop, L),
+  δ(bad, @[`X`], aa, `1`, L),
+  δ(bab, @[`1*`], bae, `1`, R),
+  δ(bae, @[`$`, `X`, `0`, `1`, `0*`, `1*`], bae, noop, R),
+  δ(bae, @[`_`], baf, noop, L),
+  δ(baf, @[`0`, `1`], baf, noop, L),
+  δ(baf, @[`X`], ba, `0`, L),
+  δ(bab, @[`0`, `1`], bab, noop, L),
+
+  δ(bba, @[`0`, `1`], bba, noop, L),
+  δ(bba, @[`$`], bbb, noop, L),
+  δ(bbb, @[`0*`], bbc, `0`, R),
+  δ(bbc, @[`$`, `X`, `0`, `1`, `0*`, `1*`], bbc, noop, R),
+  δ(bbc, @[`_`], bbd, noop, L),
+  δ(bbd, @[`0`, `1`], bbd, noop, L),
+  δ(bbd, @[`X`], ba, `0`, L),
+  δ(bbb, @[`1*`], bbe, `1`, R),
+  δ(bbe, @[`$`, `X`, `0`, `1`, `0*`, `1*`], bbe, noop, R),
+  δ(bbe, @[`_`], bbf, noop, L),
+  δ(bbf, @[`0`, `1`], bbf, noop, L),
+  δ(bbf, @[`X`], ba, `1`, L),
+  δ(bbb, @[`$`], bbc, noop, R),
+  δ(bbb, @[`0`, `1`], bbb, noop, L),
+
+  δ(za, @[`0`, `1`], za, noop, L),
+  δ(za, @[`$`], zb, noop, R),
+
+  δ(zb, @[`0`], zc, `1`, R),
+  δ(zb, @[`1`], zb, `1`, R),
+  δ(zb, @[`_`], zd, `1`, R),
+
+  δ(zc, @[`0`], zc, `0`, R),
+  δ(zc, @[`1`], zb, `0`, R),
+  δ(zc, @[`_`], zd, `0`, R),
+
+  δ(zd, @[`_`], sa, `$`, R)
+]
+
+proc print(state: State, tape: Tape, position: int) =
+  stdout.write($state)
+  for i, s in enumerate(tape):
+    if i == position:
+      stdout.write("[" & $s & "]")
+    elif s == `$`:
+      stdout.write(" ")
+    else:
+      stdout.write($s)
+  stdout.write("\n")
+
+var state = ca
+var position = 0
+var tape = @[`_`]
+
+proc step() =
+  # print(state, tape, position)
+  for δ in turing_machine:
+    if state == δ.current_state and tape.get(position) in δ.read_symbol:
+      state = δ.next_state
+      if δ.write_symbol != noop: tape.set(position, δ.write_symbol)
+      if δ.move_direction == L: position.dec
+      elif δ.move_direction == R: position.inc
+      return
+  echo "Invalid state! crashing"
+  quit()
+
+while true:
+  step()