From e650a80856edc1d1df1f163c3f84082455717fa0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Mon, 18 Mar 2019 18:43:51 +0100
Subject: Compleately redid file structure.

---
 monad/monoid.scm | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 monad/monoid.scm

(limited to 'monad/monoid.scm')

diff --git a/monad/monoid.scm b/monad/monoid.scm
new file mode 100644
index 0000000..4b10a72
--- /dev/null
+++ b/monad/monoid.scm
@@ -0,0 +1,26 @@
+;;; ???
+(define-module (monad monoid)
+  #:use-module (oop goops)
+  #:use-module (srfi srfi-1)
+  #:export (null mappend <>))
+
+(define-generic null)
+(define-generic mappend)
+
+(define (<> . args)
+  (fold mappend (null (car args)) (reverse args)))
+
+;;; Lists
+
+(define-method (mappend (a <pair>) (b <pair>))
+  (append a b))
+(define-method (mappend (a <pair>) (b <null>)) a)
+(define-method (mappend (a <null>) (b <pair>)) b)
+(define-method (mappend (a <null>) (b <null>)) '())
+(define-method (null (a <pair>)) '())
+(define-method (null (a <null>)) '())
+
+;;; Strings
+(define-method (mappend (a <string>) (b <string>))
+  (string-append a b))
+(define-method (null (a <string>)) "")
-- 
cgit v1.2.3