smalltalk: eight-queens classic program (sizes 1/4/5 verified)

lib/smalltalk/tests/programs.sx

@@ -82,4 +82,64 @@
      ^ b memoFib: 10")
   55)
 
+;; ── eight-queens.st (kept in sync with lib/smalltalk/tests/programs/eight-queens.st) ──
+(define
+  queens-source
+  "Object subclass: #EightQueens
+     instanceVariableNames: 'columns count size'!
+
+   !EightQueens methodsFor: 'init'!
+   init
+     size := 8.
+     columns := Array new: size.
+     count := 0.
+     ^ self!
+
+   size: n
+     size := n.
+     columns := Array new: n.
+     count := 0.
+     ^ self! !
+
+   !EightQueens methodsFor: 'access'!
+   count ^ count!
+
+   size ^ size! !
+
+   !EightQueens methodsFor: 'solve'!
+   solve
+     self placeRow: 1.
+     ^ count!
+
+   placeRow: row
+     row > size ifTrue: [count := count + 1. ^ self].
+     1 to: size do: [:col |
+       (self isSafe: col atRow: row) ifTrue: [
+         columns at: row put: col.
+         self placeRow: row + 1]]!
+
+   isSafe: col atRow: row
+     | r prevCol delta |
+     r := 1.
+     [r < row] whileTrue: [
+       prevCol := columns at: r.
+       prevCol = col ifTrue: [^ false].
+       delta := col - prevCol.
+       delta abs = (row - r) ifTrue: [^ false].
+       r := r + 1].
+     ^ true! !")
+
+(smalltalk-load queens-source)
+
+;; Backtracking is correct but slow on the spec interpreter (call/cc per
+;; method, dict-based ivar reads). 4- and 5-queens cover the corners
+;; and run in under 10s; 6+ work but would push past the test-runner
+;; timeout. The class itself defaults to size 8, ready for the JIT.
+(st-test "1 queen on 1x1 board" (evp "^ (EightQueens new size: 1) solve") 1)
+(st-test "4 queens on 4x4 board" (evp "^ (EightQueens new size: 4) solve") 2)
+(st-test "5 queens on 5x5 board" (evp "^ (EightQueens new size: 5) solve") 10)
+(st-test "EightQueens class is registered" (st-class-exists? "EightQueens") true)
+(st-test "EightQueens init sets size 8"
+  (evp "^ EightQueens new init size") 8)
+
 (list st-test-pass st-test-fail)

lib/smalltalk/tests/programs/eight-queens.st

@@ -0,0 +1,47 @@
+"Eight-queens — classic backtracking search. Counts the number of
+ distinct placements of 8 queens on an 8x8 board with no two attacking.
+ Expected count: 92."
+
+Object subclass: #EightQueens
+  instanceVariableNames: 'columns count size'!
+
+!EightQueens methodsFor: 'init'!
+init
+  size := 8.
+  columns := Array new: size.
+  count := 0.
+  ^ self!
+
+size: n
+  size := n.
+  columns := Array new: n.
+  count := 0.
+  ^ self! !
+
+!EightQueens methodsFor: 'access'!
+count ^ count!
+
+size ^ size! !
+
+!EightQueens methodsFor: 'solve'!
+solve
+  self placeRow: 1.
+  ^ count!
+
+placeRow: row
+  row > size ifTrue: [count := count + 1. ^ self].
+  1 to: size do: [:col |
+    (self isSafe: col atRow: row) ifTrue: [
+      columns at: row put: col.
+      self placeRow: row + 1]]!
+
+isSafe: col atRow: row
+  | r prevCol delta |
+  r := 1.
+  [r < row] whileTrue: [
+    prevCol := columns at: r.
+    prevCol = col ifTrue: [^ false].
+    delta := col - prevCol.
+    delta abs = (row - r) ifTrue: [^ false].
+    r := r + 1].
+  ^ true! !

plans/smalltalk-on-sx.md

@@ -71,7 +71,7 @@ Core mapping:
 - [x] `ifTrue:` / `ifFalse:` / `ifTrue:ifFalse:` / `ifFalse:ifTrue:` as block sends, plus `and:`/`or:` short-circuit, eager `&`/`|`, `not`. Implemented in `st-bool-send` (eval iteration); pinned by 24 tests in `lib/smalltalk/tests/conditional.sx` covering laziness of the non-taken branch, every keyword variant, return type generality, nested ifs, closures over outer locals, and an idiomatic `myMax:and:` method. Parser now also accepts a bare `|` as a binary selector (it was emitted by the tokenizer as `bar` and unhandled by `parse-binary-message`, which silently truncated `false | true` to `false`).
 - [x] Escape past returned-from method raises (the SX-level analogue of `BlockContext>>cannotReturn:`). Each method invocation allocates a small `:active-cell` `{:active true}` shared between the method-frame and any block created in its scope. `st-invoke` flips `:active false` after `call/cc` returns; `^expr` checks the captured frame's cell before invoking k and raises with a "BlockContext>>cannotReturn:" message if dead. Verified by `lib/smalltalk/tests/cannot_return.sx` (5 tests using SX `guard` to catch the raise). A normal value-returning block (no `^`) still survives across method boundaries.
 - [ ] Classic programs in `lib/smalltalk/tests/programs/`:
-  - [ ] `eight-queens.st`
+  - [x] `eight-queens.st` — backtracking N-queens search in `lib/smalltalk/tests/programs/eight-queens.st`. The `.st` source supports any board size; tests verify 1, 4, 5 queens (1, 2, 10 solutions respectively). 6+ queens are correct but too slow on the spec interpreter (call/cc + dict-based ivars per send) — they'll come back inside the test runner once the JIT lands. The 8-queens canonical case will run in production.
   - [ ] `quicksort.st`
   - [ ] `mandelbrot.st`
   - [ ] `life.st` (Conway's Life, glider gun)
@@ -108,6 +108,7 @@ Core mapping:
 
 _Newest first. Agent appends on every commit._
 
+- 2026-04-25: classic-corpus #2 eight-queens (`tests/programs/eight-queens.st`, 5 tests). Backtracking search; verified for boards of size 1, 4, 5. Larger boards are correct but too slow on the spec interpreter without JIT — `(EightQueens new size: 6) solve` is ~38s, 8-queens minutes. 382/382 total.
 - 2026-04-25: classic-corpus #1 fibonacci (`tests/programs/fibonacci.st` + `tests/programs.sx`, 13 tests). Added `smalltalk-load` chunk loader, class-side `subclass:instanceVariableNames:` (and longer Pharo variants), `Array new:` size, `methodsFor:`/`category:` no-ops, `st-split-ivars`. 377/377 total.
 - 2026-04-25: cannotReturn: implemented (`lib/smalltalk/tests/cannot_return.sx`, 5 tests). Each method-invocation gets an `{:active true}` cell shared with its blocks; `st-invoke` flips it on exit; `^expr` raises if the cell is dead. Tests use SX `guard` to catch the raise. Non-`^` blocks unaffected. 364/364 total.
 - 2026-04-25: `ifTrue:` / `ifFalse:` family pinned (`lib/smalltalk/tests/conditional.sx`, 24 tests) + parser fix: `|` is now accepted as a binary selector in expression position (tokenizer still emits it as `bar` for block param/temp delimiting; `parse-binary-message` accepts both). Caught by `false | true` truncating silently to `false`. 359/359 total.