1 files changed, 28 insertions, 0 deletions
diff --git a/data/writer.scm b/data/writer.scm
new file mode 100644
index 0000000..b79c670
--- /dev/null
+++ b/data/writer.scm
@@ -0,0 +1,28 @@
+(define-module (data writer)
+  #:use-module (oop goops)
+  #:use-module (ice-9 match)
+  #:use-module (data monoid)
+  #:use-module (control monad)
+  #:export (writer))
+
+(read-enable 'curly-infix)
+
+(define-class <writer> ()
+  (value #:init-keyword #:value)
+  (monoid #:init-keyword #:monoid))
+
+(define (writer value context)
+  (make <writer>
+    #:value value
+    #:monoid context))
+
+(define-method (>>= (this <writer>)
+                    (proc <procedure>))
+  (match this (($ <writer> value monoid)
+               (match (proc value)
+                 (($ <writer> nval ncontext)
+                  (writer nval { monoid <> ", " <> ncontext }))))))
+
+(define-method (write (this <writer>) port)
+  (match this (($ <writer> value monoid)
+               (format port "[Writer ~s, ~s]" value monoid))))