HS: remove .class from .coll when it matches .filter

Parser produces remove-class-when AST node; compiler emits
filter + for-each pattern matching add-class-when.

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

lib/hyperscript/compiler.sx

@@ -1571,6 +1571,35 @@
                         (quote dom-remove-class)
                         (if (nil? raw-tgt) (quote me) (hs-to-sx raw-tgt))
                         (nth ast 1)))))
+                ((= head (quote remove-class-when))
+                  (let
+                    ((cls (nth ast 1))
+                      (raw-tgt (nth ast 2))
+                      (when-cond (nth ast 3)))
+                    (let
+                      ((tgt-expr (cond
+                                   ((and (list? raw-tgt) (= (first raw-tgt) (quote query)))
+                                     (list (quote hs-query-all) (nth raw-tgt 1)))
+                                   (true (hs-to-sx raw-tgt)))))
+                      (list
+                        (quote let)
+                        (list
+                          (list
+                            (quote __hs-matched)
+                            (list
+                              (quote filter)
+                              (list
+                                (quote fn)
+                                (list (quote it))
+                                (hs-to-sx when-cond))
+                              tgt-expr)))
+                        (list
+                          (quote for-each)
+                          (list
+                            (quote fn)
+                            (list (quote it))
+                            (list (quote dom-remove-class) (quote it) cls))
+                          (quote __hs-matched))))))
                 ((= head (quote remove-element))
                   (let
                     ((tgt (nth ast 1)))

lib/hyperscript/parser.sx

@@ -1133,12 +1133,17 @@
                 (collect-classes!)
                 (let
                   ((tgt (if (match-kw "from") (parse-expr) (list (quote beingTold)))))
-                  (if
+                  (let
-                    (empty? extra-classes)
+                    ((when-clause (if (match-kw "when") (parse-expr) nil)))
-                    (list (quote remove-class) cls tgt)
+                    (if
-                    (cons
+                      (empty? extra-classes)
-                      (quote multi-remove-class)
+                      (if
-                      (cons tgt (cons cls extra-classes)))))))
+                        when-clause
+                        (list (quote remove-class-when) cls tgt when-clause)
+                        (list (quote remove-class) cls tgt))
+                      (cons
+                        (quote multi-remove-class)
+                        (cons tgt (cons cls extra-classes))))))))
             ((= (tp-type) "attr")
               (let
                 ((attr-name (get (adv!) "value")))

shared/static/wasm/sx/hs-compiler.sx

@@ -1571,6 +1571,35 @@
                         (quote dom-remove-class)
                         (if (nil? raw-tgt) (quote me) (hs-to-sx raw-tgt))
                         (nth ast 1)))))
+                ((= head (quote remove-class-when))
+                  (let
+                    ((cls (nth ast 1))
+                      (raw-tgt (nth ast 2))
+                      (when-cond (nth ast 3)))
+                    (let
+                      ((tgt-expr (cond
+                                   ((and (list? raw-tgt) (= (first raw-tgt) (quote query)))
+                                     (list (quote hs-query-all) (nth raw-tgt 1)))
+                                   (true (hs-to-sx raw-tgt)))))
+                      (list
+                        (quote let)
+                        (list
+                          (list
+                            (quote __hs-matched)
+                            (list
+                              (quote filter)
+                              (list
+                                (quote fn)
+                                (list (quote it))
+                                (hs-to-sx when-cond))
+                              tgt-expr)))
+                        (list
+                          (quote for-each)
+                          (list
+                            (quote fn)
+                            (list (quote it))
+                            (list (quote dom-remove-class) (quote it) cls))
+                          (quote __hs-matched))))))
                 ((= head (quote remove-element))
                   (let
                     ((tgt (nth ast 1)))

shared/static/wasm/sx/hs-parser.sx

@@ -1133,12 +1133,17 @@
                 (collect-classes!)
                 (let
                   ((tgt (if (match-kw "from") (parse-expr) (list (quote beingTold)))))
-                  (if
+                  (let
-                    (empty? extra-classes)
+                    ((when-clause (if (match-kw "when") (parse-expr) nil)))
-                    (list (quote remove-class) cls tgt)
+                    (if
-                    (cons
+                      (empty? extra-classes)
-                      (quote multi-remove-class)
+                      (if
-                      (cons tgt (cons cls extra-classes)))))))
+                        when-clause
+                        (list (quote remove-class-when) cls tgt when-clause)
+                        (list (quote remove-class) cls tgt))
+                      (cons
+                        (quote multi-remove-class)
+                        (cons tgt (cons cls extra-classes))))))))
             ((= (tp-type) "attr")
               (let
                 ((attr-name (get (adv!) "value")))