X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/fringe/blobdiff_plain/652d4a587e0ab95a9673ca1c8fd6f109a0df6a25..8a4f4f075a6e2e90039b172242097a4eca48d60b:/scheme-fringe.scm

diff --git a/scheme-fringe.scm b/scheme-fringe.scm
index 0dc93df..47b1266 100644
--- a/scheme-fringe.scm
+++ b/scheme-fringe.scm
@@ -3,8 +3,6 @@
 ;;; Scheme implementation of a `same-fringe' solver.  Assumes Chicken, but
 ;;; should port easily.
 
-(use syntax-case)			; Chicken-specfic
-
 ;;;--------------------------------------------------------------------------
 ;;; Utilities.
 
@@ -76,8 +74,8 @@
     ((define-generator (name . args) . body)
      (define (name . args)
        (make-coroutine (lambda ()
-                         (begin . body)
-                         (resume (calling-coroutine) #f #f)))))))
+			 (begin . body)
+			 (resume (calling-coroutine) #f #f)))))))
 
 (define (yield object)
   ;; Yield OBJECT from a generator.  The generator protocol returns two
@@ -86,14 +84,23 @@
 
   (with-values () (resume (calling-coroutine) object #t) #f))
 
+(define (reduce-generator func init gen)
+  ;; Call FUNC for each item in the generator GEN.
+  ;;
+  ;; We maintain a STATE, which is initially INIT.  For each ITEM produced by
+  ;; the generator, we replace the state by (FUNC ITEM STATE); finally, we
+  ;; return the final state.
+
+  (let loop ((state init))
+    (with-values (item any?) (resume gen)
+      (if any?
+	  (loop (func item state))
+	  state))))
+
 (define (list-generator gen)
   ;; Collect the elements generated by GEN into a list and return it.
 
-  (let loop ((l '()))
-    (with-values (it any?) (resume gen)
-      (if any?
-	  (loop (cons it l))
-	  (reverse l)))))
+  (reverse (reduce-generator cons '() gen)))
 
 (define (same-generators? gen-a gen-b)
   ;; Return whether GEN-A and GEN-B generate the same elements in the same
@@ -161,9 +168,8 @@
 (define (main args)
   (cond ((null? args) (error "bad args"))
 	((null? (cdr args))
-	 (do ((l (list-generator (fringe (parse-tree (car args)))) (cdr l)))
-	     ((null? l))
-	   (write-char (car l)))
+	 (reduce-generator (lambda (ch ?) (write-char ch)) #f
+			   (fringe (parse-tree (car args))))
 	 (newline))
 	((null? (cddr args))
 	 (display (if (same-generators? (fringe (parse-tree (car args)))