fixed pattern problem:

now, a normal rule can be inside common-%. this will work:
    (common-% "foo" ("%.c") (run (gcc -o ,($@) ,($<))))

added head->rc/-%/-rx, tail->rc/-%/-rx

make.scm

@@ -25,6 +25,12 @@
 (define (file->rc target prereqs thunk)
   (make-rc target prereqs file thunk))
 
+(define (head->rc target prereqs thunk)
+  (make-rc target prereqs head thunk))
+
+(define (tail->rc target prereqs thunk)
+  (make-rc target prereqs tail thunk))
+
 (define (once->rc target prereqs thunk)
   (make-rc target prereqs once thunk))
 
@@ -53,11 +59,13 @@
 			    pattern 'pre 1 match 3 'post))
 
 (define (%-pattern->match pattern no)
-  (match:substring (regexp-search (rx (: (submatch (: bos (* any)))
-					 (submatch "%") 
-					 (submatch (: (* any) eos))))
-				  pattern)
-		   no))
+  (let ((re (rx (: (submatch (: bos (* any)))
+		   (submatch "%") 
+		   (submatch (: (* any) eos)))))
+	(found-%? (regexp-search (rx (: "%")) pattern)))
+    (if found-%?
+	(match:substring (regexp-search re pattern) no)
+	(if (= no 2) pattern ""))))
 
 (define (%-pattern->rx pattern)
   (let* ((left (%-pattern->match pattern 1))
@@ -75,6 +83,12 @@
 (define (file-rx target prereqs thunk)
   (rx->func string=? target prereqs file thunk))
 
+(define (head-rx target prereqs thunk)
+  (rx->func string=? target prereqs head thunk))
+
+(define (tail-rx target prereqs thunk)
+  (rx->func string=? target prereqs tail thunk))
+
 (define (once-rx target prereqs thunk)
   (rx->func string=? target prereqs once thunk))
 
@@ -104,6 +118,12 @@
 (define (file-% target prereqs thunk)
   (%->func string=? target prereqs file thunk))
 
+(define (head-% target prereqs thunk)
+  (%->func string=? target prereqs head thunk))
+
+(define (tail-% target prereqs thunk)
+  (%->func string=? target prereqs tail thunk))
+
 (define (once-% target prereqs thunk)
   (%->func string=? target prereqs once thunk))