Improving example codes.

docs/decoupled.md

@@ -176,12 +176,28 @@ def reversi(arr):
 def reversi(arr):
     """Reverses a list."""
     reved = []
-    for i in range(len(arr)):
-        reved.append(arr[len(arr) - 1 - i])
+    for i in reversed(range(len(arr))):
+        reved.append(arr[i])
     return reved
 ```
 ````
 
+````{tabbed} Even better code using list indexing
+```
+def reversi(arr):
+    """Reverses a list."""
+    return arr[::-1]
+```
+````
+
+````{tabbed} Even better code version using built-in functions
+```
+def reversi(arr):
+    """Reverses a list."""
+    return list(reversed(arr))
+```
+````
+
 Functions with side effects can be hard to reason about: you often need to understand their internals and state in order to use them properly. They're also harder to test. **Not every function with side effects is problematic, however**. My pragmatic advice is to first learn to spot and understand pure functions. Then organize your code so that many functions are pure, and those that are not are well-behaved.
 
 ```{figure} figures/pure-impure.svg