js-on-sx: hoist var across nested blocks; var-decls become set!

JS var is function-scoped, but the transpiler only collected
top-level vars and re-emitted (define) everywhere; for-body var
shadowed the outer (un-hoisted) scope. Three-part fix:
1. js-collect-var-names recurses into js-block/js-for/js-while
   /js-do-while/js-if/js-try/js-switch/js-for-of-in;
2. var-kind decls emit (set! ...) instead of (define ...) since
   the binding is already created at function scope;
3. js-block uses js-transpile-stmt-list (no re-hoist) instead of
   js-transpile-stmts.
built-ins/Array: 17/45 → 18/45, String: 77/99 → 78/99.
conformance.sh: 148/148.

lib/js/transpile.sx

@@ -116,7 +116,8 @@
           ((js-tag? ast "js-arrow")
             (js-transpile-arrow (nth ast 1) (nth ast 2)))
           ((js-tag? ast "js-program") (js-transpile-stmts (nth ast 1)))
-          ((js-tag? ast "js-block") (js-transpile-stmts (nth ast 1)))
+          ((js-tag? ast "js-block")
+            (cons (js-sym "begin") (js-transpile-stmt-list (nth ast 1))))
           ((js-tag? ast "js-exprstmt") (js-transpile (nth ast 1)))
           ((js-tag? ast "js-empty") nil)
           ((js-tag? ast "js-var")
@@ -509,11 +510,55 @@
     (stmts)
     (cond
       ((empty? stmts) (list))
-      ((and (list? (first stmts)) (js-tag? (first stmts) "js-var") (= (nth (first stmts) 1) "var"))
+      (else
         (append
-          (js-collect-var-decl-names (nth (first stmts) 2))
-          (js-collect-var-names (rest stmts))))
-      (else (js-collect-var-names (rest stmts))))))
+          (js-collect-var-names-stmt (first stmts))
+          (js-collect-var-names (rest stmts)))))))
+
+(define
+  js-collect-var-names-stmt
+  (fn
+    (stmt)
+    (cond
+      ((not (list? stmt)) (list))
+      ((and (js-tag? stmt "js-var") (= (nth stmt 1) "var"))
+        (js-collect-var-decl-names (nth stmt 2)))
+      ((js-tag? stmt "js-block") (js-collect-var-names (nth stmt 1)))
+      ((js-tag? stmt "js-for")
+        (append
+          (js-collect-var-names-stmt (nth stmt 1))
+          (js-collect-var-names-stmt (nth stmt 4))))
+      ((js-tag? stmt "js-for-of-in")
+        (js-collect-var-names-stmt (nth stmt 4)))
+      ((js-tag? stmt "js-while")
+        (js-collect-var-names-stmt (nth stmt 2)))
+      ((js-tag? stmt "js-do-while")
+        (js-collect-var-names-stmt (nth stmt 1)))
+      ((js-tag? stmt "js-if")
+        (append
+          (js-collect-var-names-stmt (nth stmt 2))
+          (if (>= (len stmt) 4) (js-collect-var-names-stmt (nth stmt 3)) (list))))
+      ((js-tag? stmt "js-try")
+        (append
+          (js-collect-var-names-stmt (nth stmt 1))
+          (if (and (>= (len stmt) 3) (list? (nth stmt 2)))
+              (js-collect-var-names-stmt (nth (nth stmt 2) 2))
+              (list))
+          (if (>= (len stmt) 4) (js-collect-var-names-stmt (nth stmt 3)) (list))))
+      ((js-tag? stmt "js-switch")
+        (js-collect-var-names-cases (nth stmt 2)))
+      (else (list)))))
+
+(define
+  js-collect-var-names-cases
+  (fn
+    (cases)
+    (cond
+      ((empty? cases) (list))
+      (else
+        (append
+          (js-collect-var-names (nth (first cases) 2))
+          (js-collect-var-names-cases (rest cases)))))))
 
 (define
   js-dedup-names
@@ -985,12 +1030,12 @@
 
 (define
   js-transpile-var
-  (fn (kind decls) (cons (js-sym "begin") (js-vardecl-forms decls))))
+  (fn (kind decls) (cons (js-sym "begin") (js-vardecl-forms decls (= kind "var")))))
 
 (define
   js-vardecl-forms
   (fn
-    (decls)
+    (decls is-var)
     (cond
       ((empty? decls) (list))
       (else
@@ -1000,10 +1045,10 @@
             ((js-tag? d "js-vardecl")
               (cons
                 (list
-                  (js-sym "define")
+                  (js-sym (if is-var "set!" "define"))
                   (js-sym (nth d 1))
                   (js-transpile (nth d 2)))
-                (js-vardecl-forms (rest decls))))
+                (js-vardecl-forms (rest decls) is-var)))
             ((js-tag? d "js-vardecl-obj")
               (let
                 ((names (nth d 1))
@@ -1014,7 +1059,7 @@
                   (js-vardecl-obj-forms
                     names
                     tmp-sym
-                    (js-vardecl-forms (rest decls))))))
+                    (js-vardecl-forms (rest decls) is-var)))))
             ((js-tag? d "js-vardecl-arr")
               (let
                 ((names (nth d 1))
@@ -1026,7 +1071,7 @@
                     names
                     tmp-sym
                     0
-                    (js-vardecl-forms (rest decls))))))
+                    (js-vardecl-forms (rest decls) is-var)))))
             (else (error "js-vardecl-forms: unexpected decl"))))))))
 
 (define