From a1b1d10ad5fc505f8b83ac6976e5eb68b87427ff Mon Sep 17 00:00:00 2001
From: Masaya Tojo <masaya@tojo.tokyo>
Date: Wed, 12 Jun 2024 02:43:00 +0900
Subject: Add group modules

---
 algebraic-structures.egg                      |  3 +++
 algebraic-structures.group.make.scm           | 16 ++++++++++++++++
 algebraic-structures.group.number.product.scm |  8 ++++++++
 algebraic-structures.group.number.sum.scm     |  8 ++++++++
 tests/run.scm                                 | 13 +++++++++++++
 5 files changed, 48 insertions(+)
 create mode 100644 algebraic-structures.group.make.scm
 create mode 100644 algebraic-structures.group.number.product.scm
 create mode 100644 algebraic-structures.group.number.sum.scm

diff --git a/algebraic-structures.egg b/algebraic-structures.egg
index 9b21678..bf62bd3 100644
--- a/algebraic-structures.egg
+++ b/algebraic-structures.egg
@@ -16,6 +16,9 @@
   (extension algebraic-structures.monoid.number.product.base)
   (extension algebraic-structures.monoid.number.product)
   (extension algebraic-structures.monoid.make.fold)
+  (extension algebraic-structures.group.make)
+  (extension algebraic-structures.group.number.sum)
+  (extension algebraic-structures.group.number.product)
   (extension algebraic-structures.foldable.make)
   (extension algebraic-structures.foldable.list.base)
   (extension algebraic-structures.foldable.list)
diff --git a/algebraic-structures.group.make.scm b/algebraic-structures.group.make.scm
new file mode 100644
index 0000000..7568ac9
--- /dev/null
+++ b/algebraic-structures.group.make.scm
@@ -0,0 +1,16 @@
+(functor ((algebraic-structures group make) (M (<> unit inv)))
+    (<> unit inv pow)
+  (import M
+          scheme
+          (chicken base))
+
+  (define (pow x n)
+    (assert (exact-integer? n))
+    (if (negative? n)
+        (pow (inv x) (- n))
+        (let loop ((i n)
+                   (acc unit))
+          (if (= i 0)
+              acc
+              (loop (sub1 i)
+                    (<> acc x)))))))
diff --git a/algebraic-structures.group.number.product.scm b/algebraic-structures.group.number.product.scm
new file mode 100644
index 0000000..a57cdf6
--- /dev/null
+++ b/algebraic-structures.group.number.product.scm
@@ -0,0 +1,8 @@
+(import (only (algebraic-structures group make)))
+(module (algebraic-structures group number product) = (algebraic-structures group make)
+  (import scheme
+          (chicken module)
+          (algebraic-structures monoid number product))
+  (export <> unit inv)
+
+  (define (inv x) (/ x)))
diff --git a/algebraic-structures.group.number.sum.scm b/algebraic-structures.group.number.sum.scm
new file mode 100644
index 0000000..2bb7331
--- /dev/null
+++ b/algebraic-structures.group.number.sum.scm
@@ -0,0 +1,8 @@
+(import (only (algebraic-structures group make)))
+(module (algebraic-structures group number sum) = (algebraic-structures group make)
+  (import scheme
+          (chicken module)
+          (algebraic-structures monoid number sum))
+  (export <> unit inv)
+
+  (define (inv x) (- x)))
diff --git a/tests/run.scm b/tests/run.scm
index ed2cd8f..6b6a74e 100644
--- a/tests/run.scm
+++ b/tests/run.scm
@@ -107,6 +107,19 @@
 
 (test-end "monoid")
 
+(test-begin "group")
+
+(import (prefix (algebraic-structures group number product) product:))
+(import (prefix (algebraic-structures group number sum) sum:))
+
+(test -9 (sum:inv 9))
+(test 9 (sum:pow 3 3))
+
+(test 1/9 (product:inv 9))
+(test 9 (product:pow 3 2))
+
+(test-end "group")
+
 (test-begin "functor")
 
 (test '((a) (b) (c)) (list:map list '(a b c)))
-- 
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