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+// Conway's Game of Life in Baba Yaga
+
+// headAt: return the element at index i from list xs
+headAt : xs i -> with (tmp : slice xs i (i + 1)) -> tmp.0;
+
+// get2: 2D index for a grid (list of lists)
+get2 : grid r c -> headAt (headAt grid r) c;
+
+// safeGet2: bounds-checked 2D get; returns 0 when out of bounds
+safeGet2 : grid r c ->
+  with (
+    rows : length grid;
+    cols : length (headAt grid 0);
+    rOk  : (r >= 0) and (r < rows);
+    cOk  : (c >= 0) and (c < cols);
+  ) ->
+    when (rOk and cOk) is
+      true then get2 grid r c
+      _    then 0;
+
+// range [lo, hi) as a list of Int
+range : lo hi ->
+  when (lo >= hi) is
+    true then []
+    _    then prepend lo (range (lo + 1) hi);
+
+// sum a list of numbers
+sum : xs -> reduce (acc x -> acc + x) 0 xs;
+
+// deltas for neighborhood offsets
+deltas : [-1, 0, 1];
+
+// neighborsValues: list of neighbor cell values for (r,c)
+neighborsValues : grid r c ->
+  reduce (acc dr ->
+    reduce (acc2 dc ->
+      when ((dr = 0) and (dc = 0)) is
+        true then acc2
+        _    then append acc2 (safeGet2 grid (r + dr) (c + dc))
+    ) acc deltas
+  ) [] deltas;
+
+// count live neighbors at (r,c)
+countNeighbors : grid r c -> sum (neighborsValues grid r c);
+
+// nextCell: apply Game of Life rules at (r,c)
+nextCell : grid r c ->
+  with (
+    cell    : get2 grid r c;
+    n       : countNeighbors grid r c;
+    isAlive : cell = 1;
+    born    : (cell = 0) and (n = 3);
+    survive : isAlive and ((n = 2) or (n = 3));
+  ) ->
+    when survive is
+      true then 1
+      _    then when born is true then 1 _ then 0;
+
+// build next row r given width w
+rowNext : grid w r -> map (c -> nextCell grid r c) (range 0 w);
+
+// Single simulation step for the entire grid
+step : grid ->
+  with (
+    h : length grid;
+    w : length (headAt grid 0);
+  ) -> map (r -> rowNext grid w r) (range 0 h);
+
+// Demo: glider pattern in a 5x5 grid
+g0 : [
+  [0, 1, 0, 0, 0],
+  [0, 0, 1, 0, 0],
+  [1, 1, 1, 0, 0],
+  [0, 0, 0, 0, 0],
+  [0, 0, 0, 0, 0]
+];
+
+g1 : step g0;
+g2 : step g1;
+g3 : step g2;
+g4 : step g3;
+
+// Print successive generations
+io.out g0;
+io.out g1;
+io.out g2;
+io.out g3;
+io.out g4;
+
+