semen: extract counting header length into a function

semen.scm

@@ -144,12 +144,15 @@
 (define (comment-form? f)
   (and (pair? f) (eq? (car f) 'comment)))
 
+(define (fn-header-length fn-form)
+  (if (memq (first fn-form) '(pub extern)) 5 4))
+
 (define (strip-fn-header-comments fn-form)
   ;; Remove comment forms from the function header
   ;; ([pub|extern] fn name arglist rettype) so the positional accessors
   ;; below are not shifted. Comments in the body are left in place as
   ;; ordinary statements and preserved into the generated C.
-  (let ((header-count (if (memq (car fn-form) '(pub extern)) 5 4)))
+  (let ((header-count (fn-header-length fn-form)))
     ;; This always rebuilds the list, so the location has to be carried
     ;; over explicitly -- otherwise every function loses it
     (copy-form-source!
@@ -265,13 +268,9 @@ Returns #f if the form is not a function, returns the form otherwise"
   "Returns all except body"
   (assert (sex-fn? fn-form)
           (fmt #f "Form " fn-form " is not a function"))
-  (if (sex-fn-public? fn-form)
-      (take fn-form 5)
-      (take fn-form 4)))
+  (take fn-form (fn-header-length fn-form)))
 
 (define (sex-fn-body fn-form)
   (assert (sex-fn? fn-form)
           (fmt #f "Form " fn-form " is not a function"))
-  (if (sex-fn-public? fn-form)
-      (drop fn-form 5)
-      (drop fn-form 4)))
+  (drop fn-form (fn-header-length fn-form)))