1 files changed, 39 insertions, 0 deletions
diff --git a/algebraic-structs.foldable.make.scm b/algebraic-structs.foldable.make.scm
new file mode 100644
index 0000000..46b4dd5
--- /dev/null
+++ b/algebraic-structs.foldable.make.scm
@@ -0,0 +1,39 @@
+(functor ((algebraic-structs foldable make) (F (foldl foldr)))
+    (foldl foldr length find any every ->list)
+  (import (except scheme length) F
+          (only (chicken base) add1 call/cc))
+
+  (define (length xs)
+    (foldl (lambda (acc _) (add1 acc))
+           0
+           xs))
+
+  (define (find p? xs)
+    (call/cc
+     (lambda (k)
+       (foldl (lambda (acc e)
+                (if (p? e)
+                    (k e)
+                    acc))
+              #f
+              xs))))
+
+  (define (any pred xs)
+    (call/cc
+     (lambda (return)
+       (foldl (lambda (acc e)
+                (cond ((pred e) => return)
+                      (else acc)))
+              #f
+              xs))))
+
+  (define (every pred xs)
+    (call/cc
+     (lambda (return)
+       (foldl (lambda (acc e)
+                (or (pred e) (return #f)))
+              #t
+              xs))))
+
+  (define (->list xs)
+    (foldr cons '() xs)))