add `other-siblings`

pollen/pagetree.rkt

@@ -175,6 +175,23 @@
  (check-false (siblings 'invalid-key test-pagetree)))
 
 
+(define+provide/contract (other-siblings pnish [pt-or-path (current-pagetree)])
+  (((or/c #f pagenodeish?)) ((or/c pagetree? pathish?)) . ->* . (or/c #f pagenodes?))  
+  (define sibs (for/list ([sib (in-list (or (siblings pnish pt-or-path) empty))]
+                          #:unless (eq? sib (->pagenode pnish)))
+                         sib))
+  (and (pair? sibs) sibs))
+
+(module-test-external
+ (define test-pagetree `(pagetree-main foo bar (one (two three four))))
+ (check-equal? (other-siblings 'one test-pagetree) '(foo bar))
+ (check-equal? (other-siblings 'foo test-pagetree) '(bar one))
+ (check-equal? (other-siblings 'two test-pagetree) #f)
+ (check-equal? (other-siblings 'three test-pagetree) '(four))
+ (check-false (other-siblings #f test-pagetree))
+ (check-false (other-siblings 'invalid-key test-pagetree)))
+
+
 ;; private helper function.
 ;; only takes pt as input.
 ;; used by `pagetree?` predicate, so can't use `pagetree?` contract.

pollen/private/ts.rktd

@@ -1 +1 @@
-1494629838
+1494630905

pollen/scribblings/pagetree.scrbl

@@ -352,15 +352,29 @@ Find the child pagenodes of @racket[_p] within @racket[_pagetree]. Return @racke
 [p (or/c #f pagenodeish?)]
 [pagetree (or/c pagetree? pathish?) (current-pagetree)])
 (or/c #f pagenode?)]
-Find the sibling pagenodes of @racket[_p] within @racket[_pagetree]. The list will include @racket[_p] itself. But the function will still return @racket[#f] if @racket[_pagetree] is @racket[#f].
+Find the sibling pagenodes of @racket[_p] within @racket[_pagetree]. The result includes @racket[_p] itself. But the function will still return @racket[#f] if @racket[_pagetree] is @racket[#f].
 
 @examples[#:eval my-eval
-(current-pagetree '(root (mama.html son.html daughter.html) uncle.html))
+(current-pagetree '(root (mama.html son.html daughter.html)))
 (siblings 'son.html)
 (siblings 'daughter.html)
 (siblings 'mama.html)
 ]
 
+@defproc[
+(other-siblings
+[p (or/c #f pagenodeish?)]
+[pagetree (or/c pagetree? pathish?) (current-pagetree)])
+(or/c #f pagenode?)]
+Like @racket[siblings], but the result does not include @racket[_p] itself.
+
+@examples[#:eval my-eval
+(current-pagetree '(root (mama.html son.html daughter.html)))
+(other-siblings 'son.html)
+(other-siblings 'daughter.html)
+(other-siblings 'mama.html)
+]
+
 
 @deftogether[(