From 1f60d4a7e3e4804ac68592bdbb7e9827fee1adbf Mon Sep 17 00:00:00 2001
From: Masaya Tojo <masaya@tojo.tokyo>
Date: Fri, 14 Jun 2024 10:50:44 +0900
Subject: Add semigroup

---
 algebraic-structures.egg           |  1 +
 algebraic-structures.semigroup.scm |  2 ++
 tests/run.scm                      | 39 +++++++++++++++++++++++++++++---------
 3 files changed, 33 insertions(+), 9 deletions(-)
 create mode 100644 algebraic-structures.semigroup.scm

diff --git a/algebraic-structures.egg b/algebraic-structures.egg
index 1c9e574..ba71745 100644
--- a/algebraic-structures.egg
+++ b/algebraic-structures.egg
@@ -8,6 +8,7 @@
  (dependencies matchable)
  (test-dependencies test)
  (components
+  (extension algebraic-structures.semigroup)
   (extension algebraic-structures.monoid)
   (extension algebraic-structures.monoid.fold)
   (extension algebraic-structures.group)
diff --git a/algebraic-structures.semigroup.scm b/algebraic-structures.semigroup.scm
new file mode 100644
index 0000000..3912349
--- /dev/null
+++ b/algebraic-structures.semigroup.scm
@@ -0,0 +1,2 @@
+(functor ((algebraic-structures semigroup) (S (<>))) (<>)
+  (import S))
diff --git a/tests/run.scm b/tests/run.scm
index 8d78396..6110b98 100644
--- a/tests/run.scm
+++ b/tests/run.scm
@@ -2,29 +2,43 @@
 
 (test-begin "algebraic-structures")
 
-(test-begin "monoid")
+(test-begin "semigroup")
 
-(import (algebraic-structures monoid))
+(import (algebraic-structures semigroup))
 
-(module (mod7 monoid) = (algebraic-structures monoid)
+(module (mod7 semigroup) = (algebraic-structures semigroup)
   (import scheme
           (chicken module)
           (chicken base))
-  (export <> unit)
+  (export <>)
 
   (define (<> x y)
     (assert (integer? x))
     (assert (integer? y))
     (assert (not (zero? x)))
     (assert (not (zero? y)))
-    (modulo (* x y) 7))
+    (modulo (* x y) 7)))
+
+(import (prefix (algebraic-structures semigroup) mod7:<>))
+
+(test 5 (mod7:<> 3 4))
+
+(test-end "semigroup")
+
+(import (algebraic-structures monoid))
+
+(module (mod7 monoid) = (algebraic-structures monoid)
+  (import scheme
+          (chicken module)
+          (chicken base))
+  (reexport (mod7 semigroup))
+  (export unit)
 
   (define unit 1))
 
 (import (prefix (mod7 monoid) mod7:)
         (srfi 1))
 
-(test 5 (mod7:<> 3 4))
 (test 1 mod7:unit)
 
 (test-end "monoid")
@@ -95,18 +109,25 @@
 
 (test-begin "monoid.fold")
 
-(module (product monoid) = (algebraic-structures monoid)
+(module (product semigroup) = (algebraic-structures semigroup)
   (import scheme
           (chicken base)
           (chicken module))
-  (export <> unit)
+  (export <>)
 
   (define (<> x y)
     (assert (number? x))
     (assert (not (zero? x)))
     (assert (number? y))
     (assert (not (zero? y)))
-    (* x y))
+    (* x y)))
+
+(module (product monoid) = (algebraic-structures monoid)
+  (import scheme
+          (chicken base)
+          (chicken module))
+  (reexport (product semigroup))
+  (export unit)
 
   (define unit 1))
 
-- 
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