diff --git a/users/sterni/exercises/aoc/2022/21/21.bqn b/users/sterni/exercises/aoc/2022/21/21.bqn
new file mode 100644
index 000000000..2f91f55d4
--- /dev/null
+++ b/users/sterni/exercises/aoc/2022/21/21.bqn
@@ -0,0 +1,25 @@
+⟨ImportBqnLibs, IsAsciiNum, ReadDec⟩ ← •Import "../../lib.bqn"
+⟨ReplaceAll, Split⟩ ← ImportBqnLibs "strings.bqn"
+
+i ← ": "⊸Split¨ •FLines "input"
+ReplaceInts ← {
+  𝕊 𝕩: 𝕊´ 2↑(¬∘(∧´IsAsciiNum∘⊑∘⌽)¨⊔⊢) 𝕩;
+  # TODO: Efficient replace on tokens
+  is 𝕊 es: (((•Fmt⍟(0⊸≠•Type))¨⌾(1⊸⊑) <˘⍉>is)⊸ReplaceAll⌾(1⊸⊑))¨ es
+}
+
+c ← 0
+CanEval ← (IsAsciiNum∨∊⟜"+-/* ")
+Eval ← {
+  a‿s‿b ← " " Split 𝕩
+  f ← ⊑+‿-‿×‿÷⊏˜"+-*/"⊐s
+  a F○ReadDec b
+}
+EvalExprs ← {
+  p‿e ← 2↑((∧´CanEval∘⊑∘⌽)¨⊔⊢) 𝕩
+  ev ← (Eval⌾(⊑⌽))¨ e
+  c +↩1
+  (⊑(⊑¨ev)∊˜<"root")◶⟨EvalExprs∘(ReplaceInts⟜p),1⊸⊑⊑⟩ ev
+}
+
+•Show EvalExprs ReplaceInts i
diff --git a/users/sterni/exercises/aoc/lib.bqn b/users/sterni/exercises/aoc/lib.bqn
index 37c518d1f..e870a5dfa 100644
--- a/users/sterni/exercises/aoc/lib.bqn
+++ b/users/sterni/exercises/aoc/lib.bqn
@@ -1,4 +1,5 @@
 IsAsciiNum ⇐ ('0'⊸≤∧≤⟜'9')
+IsAlpha ⇐ (('a'⊸≤∧≤⟜'z')∨('A'⊸≤∧≤⟜'Z'))
 
 # based on leah2's function
 ReadInt ⇐ {