From 3c96e1e1819d3fe68d5986cc8cb268e7698e0ab9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Fri, 16 Nov 2018 00:53:15 +0100
Subject: Add instance of fmap for <optional>.

---
 data/optional.scm | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/data/optional.scm b/data/optional.scm
index b008471..c90fec5 100644
--- a/data/optional.scm
+++ b/data/optional.scm
@@ -2,11 +2,11 @@
   #:use-module (oop goops)
   #:use-module (ice-9 match)
   #:use-module (control monad)
+  #:use-module (data functor)
   #:export (nothing just
                     nothing? just?
                     return-optional)
-  ;; TODO is this reexport needed?
-  #:re-export (>>=))
+  #:re-export (>>= >> fmap))
 
 (define-class <optional> ()
   (slot #:init-value #f
@@ -47,3 +47,8 @@
           (nothing? b))
       (nothing)
       b))
+
+(define-method (fmap (f <procedure>)
+                     (m <optional>))
+  (do x <- m
+      (return-optional (f x))))
-- 
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