document set-links-label!

svn: r14381

collects/mrlib/graph.ss

@@ -146,9 +146,10 @@
                                  label)
     (send parent add-child child)
     (send child add-parent parent dark-pen light-pen dark-brush light-brush dark-text light-text dx dy label))
+
   (define (set-links-label! parent child label)
     (send child set-parent-link-label parent label))
-  
+
   (define graph-snip-mixin
     (mixin ((class->interface snip%)) (graph-snip<%>)
       (field (children null))
@@ -163,15 +164,6 @@
       (field (parent-links null))
       (define/public (get-parent-links) parent-links)
       (define/public (get-parents) (map link-snip parent-links))
-      (define/public (set-parent-link-label parent label)
-        (let ([parent-link
-               (cond [(memf (lambda (parent-link)
-                              (eq? (link-snip parent-link) parent))
-                            parent-links)
-                      => car]
-                     [else #f])])
-          (when parent-link
-            (set-link-label! parent-link label))))
       (define/public add-parent
         (case-lambda
           [(parent) (add-parent parent #f #f #f #f)]
@@ -202,6 +194,15 @@
                  parent
                  parent-links
                  (lambda (parent parent-link) (eq? (link-snip parent-link) parent))))))
+      (define/public (set-parent-link-label parent label)
+        (let ([parent-link
+               (cond [(memf (lambda (parent-link)
+                              (eq? (link-snip parent-link) parent))
+                            parent-links)
+                      => car]
+                     [else #f])])
+          (when parent-link
+            (set-link-label! parent-link label))))
       
       (define/public (has-self-loop?)
         (memq this (get-children)))

collects/mrlib/scribblings/graph/graph-snip-intf.scrbl

@@ -60,4 +60,16 @@ this snip.
   Removes a parent snip from this snip. Be sure to remove this
   snip as a child from the argument, too.
 
-}}
+}
+
+
+@defmethod[(set-parent-link-label [parent (is-a?/c graph-snip<%>)]
+                                  [label (or/c false/c string/)])
+           void?]{
+
+  Changes the label on the edge going to the @scheme[parent] to be
+  @scheme[label].  Ignored if no such egde exists.
+
+}
+
+}

collects/mrlib/scribblings/graph/graph.scrbl

@@ -74,3 +74,12 @@ used.}
 
 Like @scheme[add-links], but with extra @scheme[dark-text] and
 @scheme[light-text] arguments to set the colors of the label.}
+
+@defproc[(set-links-label! [parent (is-a?/c graph-snip<%>)]
+                           [child (is-a?/c graph-snip<%>)]
+                           [label (or/c string? false/c)])
+          void?]{
+
+Changes the label on the edge going from @scheme[child] to
+@scheme[parent] to be @scheme[label].  If there is no existing edge
+between the two nodes, then nothing happens.}