1 files changed, 51 insertions, 0 deletions
diff --git a/examples/mod7.scm b/examples/mod7.scm
new file mode 100644
index 0000000..cfdce61
--- /dev/null
+++ b/examples/mod7.scm
@@ -0,0 +1,51 @@
+(import (algebraic-structures semigroup)
+        (algebraic-structures monoid)
+        (algebraic-structures group)
+        (algebraic-structures monoid fold)
+        (algebraic-structures list foldable))
+
+(module (mod7 semigroup) = (algebraic-structures semigroup)
+  (import scheme
+          (chicken module)
+          (chicken base))
+  (export <>)
+
+  (define (<> x y)
+    (assert (integer? x))
+    (assert (integer? y))
+    (assert (not (zero? x)))
+    (assert (not (zero? y)))
+    (modulo (* x y) 7)))
+
+(module (mod7 monoid) = (algebraic-structures monoid)
+  (import scheme
+          (chicken module)
+          (chicken base))
+  (reexport (mod7 semigroup))
+  (export unit)
+
+  (define unit 1))
+
+(module (mod7 group) = (algebraic-structures group)
+  (import scheme
+          (chicken base)
+          (chicken module)
+          matchable)
+  (reexport (mod7 monoid))
+  (export inv)
+
+  (define (inv n)
+    (assert (integer? n))
+    (assert (not (zero? n)))
+    (match (modulo n 7)
+      (1 1)
+      (2 4)
+      (3 5)
+      (4 2)
+      (5 3)
+      (6 6))))
+
+(module (mod7 fold) = ((algebraic-structures monoid fold) (mod7 monoid) (algebraic-structures list foldable)))
+
+(import (prefix (mod7 group) mod7:)
+        (prefix (mod7 fold) mod7:))