hash union

quad2/linearize.rkt

@@ -15,9 +15,7 @@
   #:pre quad?
   #:post (list-of simple-quad?)
   (let loop ([q q][attrs-context (make-quad-attrs)]) ;; returns (list-of quad?)
-    (define current-attrs (let ([qas (make-quad-attrs)])
-                            (hash-union! #:combine (λ (v1 v2) v2) qas attrs-context (quad-attrs q))
-                            qas))
+    (define current-attrs (quad-attrs-union attrs-context (quad-attrs q)))
     (define (mq es) (make-quad #:tag (quad-tag q) #:attrs current-attrs #:elems es))
     (match (quad-elems q)
       [(? null?) (list (mq null))]

quad2/quad.rkt

@@ -1,5 +1,8 @@
 #lang debug racket/base
-(require racket/contract racket/match (for-syntax racket/base racket/syntax))
+(require racket/contract
+         racket/match
+         racket/hash
+         (for-syntax racket/base racket/syntax))
 (provide (all-defined-out))
 
 (struct $point (x y) #:transparent #:mutable)
@@ -26,6 +29,12 @@
                         [(or (? symbol?) #false) #true]
                         [_ #false]))
 (define (make-quad-attrs [alist null]) (make-hasheq alist))
+
+(define (quad-attrs-union . attrss)
+  (define qas (make-quad-attrs))
+  (apply hash-union! #:combine (λ (v1 v2) v2) qas attrss)
+  qas)
+
 (define (quad-attrs? x) (hash-eq? x))
 (define (quad-elems? x) (list? x))