Return u0 when err, to avoid confusion with the ok condition. Removed the begin, which is redundant when let is used. Updated indentation.

src/pages/smart-contracts/principals.md

@@ -107,12 +107,11 @@ faucet" could be implemented as so:
  ((claimed bool)))
 
 (define-public (claim-from-faucet)
-  (if (is-none (map-get? claimed-before (tuple (sender tx-sender))))
-      (let ((requester tx-sender)) ;; set a local variable requester = tx-sender
-        (begin
-            (map-set claimed-before { sender: requester } { claimed: true })
-            (as-contract (stx-transfer? u1 tx-sender requester))))
-      (err u1)))
+  (if (is-none (map-get? claimed-before {sender: tx-sender}))
+    (let ((requester tx-sender))
+      (map-set claimed-before {sender: requester} {claimed: true})
+      (as-contract (stx-transfer? u1 tx-sender requester)))
+    (err u0)))
 ```
 
 In this example, the public function `claim-from-faucet`: