From 1fde17abca63694279707e6ea3e8b46b6845b67c Mon Sep 17 00:00:00 2001
From: pimjager <pim@pimjager.nl>
Date: Thu, 23 Jun 2016 12:38:59 +0200
Subject: [PATCH] Maybe fmap no longer edits input

---
 examples/demo/maybe.spl | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/examples/demo/maybe.spl b/examples/demo/maybe.spl
index a4b9416..b676aea 100644
--- a/examples/demo/maybe.spl
+++ b/examples/demo/maybe.spl
@@ -6,26 +6,26 @@ pure(a) :: a -> (Int, a) {
     return (1, a);
 }
 
-//note, ma is edited by reference!
 fmap(f, ma) :: (a -> b) -> (Int, a) -> (Int, b) {
+    var t = ma.snd; //copy to avoid editing ma by reference
     if (ma.fst == 0) { return ma; }
     else {
-        ma.snd = f(ma.snd);
-        return ma;
+        t = f(ma.snd);
+        return (ma.fst, t);
     }
 }
 
+
 bind(ma, f) :: (Int, a) -> (a -> (Int, b)) -> (Int, b) {
     if (ma.fst == 0) { return ma; }
     else {
-        return f(ma.snd);
+        return f(ma.snd); 
     }
 }
 
 main() {
     
     var j = pure(True);
-    var f = \b->!b;
     var n = (0, False); //ugly that we need the additional parameter
 
     var jf = fmap(\b->!b, j);
@@ -33,12 +33,12 @@ main() {
 
     var fma = \b -> pure(!b);
 
-    var bjf = bind(j, fma); //note is true because ma is passed by reference
+    var bjf = bind(j, fma); 
     bar bnf = bind(n, fma);
 
     print("fmap Just false: ", jf.fst, jf.snd, "\n");
     print("fmap Nothing: ", nf.fst, "\n");
 
-    print("bind Just True: ", bjf.fst, bjf.snd, "\n");
+    print("bind Just False: ", bjf.fst, bjf.snd, "\n");
     print("bind Nothing: ", bnf.fst, "\n");
 }
\ No newline at end of file
-- 
2.20.1