cl: Phase 6 FORMAT + substr fixes — 514/514 tests

FORMAT with ~A/~S/~D/~F/~%/~&/~T/~P/~{...~}/~^; cl-fmt-loop,
cl-fmt-find-close, cl-fmt-iterate, cl-fmt-a/cl-fmt-s helpers.
Fix substr(start,length) semantics throughout: SUBSEQ end formula
corrected to (- end start), cl-fmt-loop char extraction fixed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/common-lisp/eval.sx

@@ -191,6 +191,140 @@
                       (cl-eval-body body e5)))))))))))))
 
 
+;; ── FORMAT helpers ──────────────────────────────────────────────
+
+(define cl-fmt-a
+  (fn (arg)
+    (cond
+      ((= arg nil) "()")
+      ((= arg true) "T")
+      ((= arg false) "NIL")
+      ((string? arg) arg)
+      ((number? arg) (str arg))
+      ((list? arg)
+        (if (= (len arg) 0) "()"
+          (str "("
+               (reduce (fn (a x) (str a " " (cl-fmt-a x)))
+                       (cl-fmt-a (nth arg 0))
+                       (rest arg))
+               ")")))
+      ((and (dict? arg) (= (get arg "cl-type") "keyword"))
+        (str ":" (get arg "name")))
+      ((and (dict? arg) (= (get arg "cl-type") "char"))
+        (get arg "value"))
+      (:else (str arg)))))
+
+(define cl-fmt-s
+  (fn (arg)
+    (cond
+      ((= arg nil) "NIL")
+      ((= arg true) "T")
+      ((= arg false) "NIL")
+      ((string? arg) (str "\"" arg "\""))
+      ((number? arg) (str arg))
+      ((list? arg)
+        (if (= (len arg) 0) "NIL"
+          (str "("
+               (reduce (fn (a x) (str a " " (cl-fmt-s x)))
+                       (cl-fmt-s (nth arg 0))
+                       (rest arg))
+               ")")))
+      ((and (dict? arg) (= (get arg "cl-type") "keyword"))
+        (str ":" (get arg "name")))
+      ((and (dict? arg) (= (get arg "cl-type") "char"))
+        (str "#\\" (get arg "value")))
+      (:else (str arg)))))
+
+;; Find position of ~CH (tilde+ch) in ctrl, starting from i, tracking nesting
+(define cl-fmt-find-close
+  (fn (ctrl ch i depth)
+    (if (>= i (- (len ctrl) 1)) -1
+      (let ((c (substr ctrl i 1)))
+        (if (= c "~")
+          (let ((nxt (upcase (substr ctrl (+ i 1) 1))))
+            (cond
+              ((= nxt ch)
+                (if (= depth 0) i (cl-fmt-find-close ctrl ch (+ i 2) (- depth 1))))
+              ((or (= nxt "{") (= nxt "["))
+                (cl-fmt-find-close ctrl ch (+ i 2) (+ depth 1)))
+              (:else
+                (cl-fmt-find-close ctrl ch (+ i 2) depth))))
+          (cl-fmt-find-close ctrl ch (+ i 1) depth))))))
+
+;; Process inner ~{...~} string over each element of a list
+(define cl-fmt-iterate
+  (fn (inner items)
+    (if (= items nil) ""
+      (if (= (len items) 0) ""
+        (reduce
+          (fn (acc x)
+            (str acc (get (cl-fmt-loop inner (list x) 0 "") "out")))
+          "" items)))))
+
+;; Main format loop: returns {:out string :args remaining}
+(define cl-fmt-loop
+  (fn (ctrl args i out)
+    (if (>= i (len ctrl))
+      {:out out :args args}
+      (let ((ch (substr ctrl i 1)))
+        (if (not (= ch "~"))
+          (cl-fmt-loop ctrl args (+ i 1) (str out ch))
+          (let ((dir (if (< (+ i 1) (len ctrl))
+                       (upcase (substr ctrl (+ i 1) 1))
+                       "")))
+            (cond
+              ((= dir "A")
+                (cl-fmt-loop ctrl (rest args) (+ i 2)
+                  (str out (if (> (len args) 0) (cl-fmt-a (nth args 0)) ""))))
+              ((= dir "S")
+                (cl-fmt-loop ctrl (rest args) (+ i 2)
+                  (str out (if (> (len args) 0) (cl-fmt-s (nth args 0)) ""))))
+              ((or (= dir "D") (= dir "F") (= dir "B") (= dir "X") (= dir "O"))
+                (cl-fmt-loop ctrl (rest args) (+ i 2)
+                  (str out (if (> (len args) 0) (str (nth args 0)) ""))))
+              ((= dir "%")
+                (cl-fmt-loop ctrl args (+ i 2) (str out "\n")))
+              ((= dir "&")
+                (cl-fmt-loop ctrl args (+ i 2)
+                  (if (or (= (len out) 0)
+                          (= (substr out (- (len out) 1) 1) "\n"))
+                    out (str out "\n"))))
+              ((= dir "T")
+                (cl-fmt-loop ctrl args (+ i 2) (str out "\t")))
+              ((= dir "P")
+                (let ((arg (if (> (len args) 0) (nth args 0) 1)))
+                  (cl-fmt-loop ctrl (rest args) (+ i 2)
+                    (str out (if (= arg 1) "" "s")))))
+              ((= dir "{")
+                (let ((end-i (cl-fmt-find-close ctrl "}" (+ i 2) 0)))
+                  (if (= end-i -1)
+                    {:out (str out "~{") :args args}
+                    (let ((inner (if (> end-i (+ i 2))
+                                   (substr ctrl (+ i 2) (- end-i (+ i 2)))
+                                   "")))
+                      (let ((list-arg (if (> (len args) 0) (nth args 0) (list))))
+                        (cl-fmt-loop ctrl (rest args) (+ end-i 2)
+                          (str out (cl-fmt-iterate inner (if (= list-arg nil) (list) list-arg)))))))))
+              ((= dir "[")
+                (let ((end-i (cl-fmt-find-close ctrl "]" (+ i 2) 0)))
+                  (if (= end-i -1)
+                    {:out (str out "~[") :args args}
+                    (let ((inner (if (> end-i (+ i 2))
+                                   (substr ctrl (+ i 2) (- end-i (+ i 2)))
+                                   "")))
+                      (let ((arg (if (> (len args) 0) (nth args 0) 0)))
+                        (let ((chosen (if (= arg true) "T"
+                                        (if (= arg nil) "NIL"
+                                          (get (cl-fmt-loop inner (list arg) 0 "") "out")))))
+                          (cl-fmt-loop ctrl (rest args) (+ end-i 2)
+                            (str out chosen))))))))
+              ((= dir "~")
+                (cl-fmt-loop ctrl args (+ i 2) (str out "~")))
+              ((= dir "^")
+                {:out out :args args})
+              (:else
+                (cl-fmt-loop ctrl args (+ i 2) (str out "~" dir))))))))))
+
 ;; ── sequence/list helpers (needed by builtins) ───────────────────
 
 (define cl-member-helper
@@ -520,7 +654,7 @@
                         (start (nth args 1))
                         (end   (if (> (len args) 2) (nth args 2) nil)))
                     (if (string? seq)
-                      (if end (substr seq start (- end 1)) (substr seq start (- (len seq) 1)))
+                      (if end (substr seq start (- end start)) (substr seq start (- (len seq) start)))
                       (if (= seq nil) (list)
                         (if end (slice seq start end) (slice seq start (len seq)))))))
     "STRING"   (fn (args)
@@ -552,6 +686,12 @@
                                (reduce (fn (a c) (str a (if (dict? c) (get c "value") c))) "" x)
                                (str x)))
                              (:else x))))
+    "FORMAT"   (fn (args)
+                  (let ((dest   (nth args 0))
+                        (ctrl   (if (> (len args) 1) (nth args 1) ""))
+                        (fargs  (if (> (len args) 2) (slice args 2 (len args)) (list))))
+                    (let ((result (get (cl-fmt-loop ctrl fargs 0 "") "out")))
+                      (if (= dest nil) result nil))))
     "MAKE-LIST" (fn (args)
                    (let ((n (nth args 0)))
                      (map (fn (_) nil) (range 0 n))))))

lib/common-lisp/scoreboard.json

@@ -1,6 +1,6 @@
 {
-  "generated": "2026-05-05T12:16:51Z",
-  "total_pass": 508,
+  "generated": "2026-05-05T12:23:35Z",
+  "total_pass": 514,
   "total_fail": 0,
   "suites": [
     {"name": "Phase 1: tokenizer/reader", "pass": 79, "fail": 0},
@@ -14,6 +14,6 @@
     {"name": "Phase 4: geometry", "pass": 12, "fail": 0},
     {"name": "Phase 4: mop-trace", "pass": 13, "fail": 0},
     {"name": "Phase 5: macros+LOOP", "pass": 27, "fail": 0},
-    {"name": "Phase 6: stdlib", "pass": 44, "fail": 0}
+    {"name": "Phase 6: stdlib", "pass": 50, "fail": 0}
   ]
 }

lib/common-lisp/scoreboard.md

@@ -1,6 +1,6 @@
 # Common Lisp on SX — Scoreboard
 
-_Generated: 2026-05-05 12:16 UTC_
+_Generated: 2026-05-05 12:23 UTC_
 
 | Suite | Pass | Fail | Status |
 |-------|------|------|--------|
@@ -15,6 +15,6 @@ _Generated: 2026-05-05 12:16 UTC_
 | Phase 4: geometry | 12 | 0 | pass |
 | Phase 4: mop-trace | 13 | 0 | pass |
 | Phase 5: macros+LOOP | 27 | 0 | pass |
-| Phase 6: stdlib | 44 | 0 | pass |
+| Phase 6: stdlib | 50 | 0 | pass |
 
-**Total: 508 passed, 0 failed**
+**Total: 514 passed, 0 failed**

lib/common-lisp/tests/stdlib.sx

@@ -234,6 +234,32 @@
   (ev "(subseq \"hello\" 2)")
   "llo")
 
+;; ── FORMAT ─────────────────────────────────────────────────────────
+
+(check "format ~A"
+  (ev "(format nil \"hello ~A\" \"world\")")
+  "hello world")
+
+(check "format ~D"
+  (ev "(format nil \"~D items\" 42)")
+  "42 items")
+
+(check "format two args"
+  (ev "(format nil \"~A ~A\" 1 2)")
+  "1 2")
+
+(check "format ~A+~A=~A"
+  (ev "(format nil \"~A + ~A = ~A\" 1 2 3)")
+  "1 + 2 = 3")
+
+(check "format iterate"
+  (ev "(format nil \"~{~A~}\" (quote (1 2 3)))")
+  "123")
+
+(check "format iterate with space"
+  (ev "(format nil \"(~{~A ~})\" (quote (1 2 3)))")
+  "(1 2 3 )")
+
 ;; ── summary ──────────────────────────────────────────────────────
 
 (define stdlib-passed passed)