Let transform-modifier take PROC instead of VALUE.

1 files changed, 19 insertions, 7 deletions

diff --git a/pict.scm b/pict.scm
index db5df15..957910a 100644
--- a/pict.scm
+++ b/pict.scm
@@ -179,17 +179,29 @@ of transform lists LST."
                        (string-append key "(" val ")")))
                     lst)))
 
-(define (transform-modifier key value)
+(define (transform-modifier key proc)
+  "Return a function that replaces KEY in the transforms of a pict
+with the return value of PROC applied to the current value.  If KEY
+does not exist it is added with PROC applied to #F."
   (attribute-modifier
    'transform
    (lambda (transform-str)
      (transform-list->string
-      (cons (list key value)
-            (filter (match-lambda
-                      ((k _)
-                       (not (string=? k key)))
-                      (_ '()))
-                    (transform-string->list (or transform-str ""))))))))
+      (match (fold (lambda (item state)
+                     (match item
+                       ((k v)
+                        (if (string=? k key)
+                            (cons #t    ; replaced!
+                                  (cons (list key (proc v))
+                                        (cdr state)))
+                            (cons (car state)
+                                  (cons item (cdr state)))))))
+                   '(#f . ())
+                   (transform-string->list (or transform-str "")))
+        ((#f . items)
+         (cons (list key (proc #f))
+               items))
+        ((_ . items) items))))))
 
 (define (style-string->list styles)
   "Split the styles string into a list of lists from keys to values."