From 0660fe3b1de9f651b5b278c952c9aaabbe8325f1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miloslav=20=C4=8C=C3=AD=C5=BE?= <drummyfish@disroot.org>
Date: Fri, 19 Nov 2021 19:57:37 +0100
Subject: [PATCH] Update

---
 monad.md | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/monad.md b/monad.md
index e8714b5..a30b9ca 100644
--- a/monad.md
+++ b/monad.md
@@ -12,7 +12,37 @@ A typical example is a **maybe** monad which wraps a type such as integer to han
 2. A special function *return(X)* that converts value of given type into this maybe type, e.g. *return(3)* will return *just(3)*
 3. A special combinator *X >>= f* which takes a monadic (*maybe*) values *X* and a function *f* and does the following:
   - if *X* is *nothing*, gives back *nothing*
-  - if *X* is a value *just(N)*, gives back the value *f(N)*
+  - if *X* is a value *just(N)*, gives back the value *f(N)* (i.e. unwraps the value and hand it over to the function)
 
+Let's look at a pseudocode example of writing a safe division function. Without using the combinator it's kind of ugly:
 
-TODO: example in some lang, e.g. haskell
+```
+divSafe(x,y) = // takes two maybe values, returns a maybe value
+  if x == nothing
+    nothing else
+    if y == nothing
+      nothing else
+        if y == 0
+          nothing else
+            just(x / y)
+```
+
+With the combinator it gets much nicer (note the use of [lambda expression](lambda.md)):
+
+```
+divSafe(x,y) =
+  x >>= { a: y >== { b: if b == 0 nothing else a / b } }
+```
+
+Languages  will typicall make this even nicer with a [syntax sugar](syntax_sugar.md) such as:
+
+```
+divSafe(x,y) = do
+  a <- x,
+  b <- y,
+  if y == 0 nothing else return(a / b)
+```
+
+TODO: I/O monad
+TODO: general monad
+TODO: example in real lang, e.g. haskell