From 4d5c674e2d153fc54b8bd992c052da3f3e50a4d3 Mon Sep 17 00:00:00 2001
From: "Jonathan D.A. Jewell" <6759885+hyperpolymath@users.noreply.github.com>
Date: Fri, 9 Oct 2026 02:06:52 +0100
Subject: [PATCH] fix(examples): let hello.affine use the builtin println so
 `just jaffa hello` runs
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The example declared its own `effect IO { fn println(s: String) -> (); }`.
That declaration shadows AffineScript's builtin `println`, which already
carries the `IO` effect. `eval` then performs the declared effect, finds no
handler, and stops with "Runtime error: Unhandled effect: println" (exit 124,
affinescript's own error code; it is not a timeout).

Dropping the declaration makes check, eval, compile, preview-js and lint all
pass under affinescript 0.1.1, through `just jaffa …` and `bin/jaffa`. The
README's copy of the example gets the same change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GpUzjdhWFi26k6s7AWxYcf
---
 README.adoc           | 4 ----
 examples/hello.affine | 9 +++++----
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/README.adoc b/README.adoc
index a881502..40469bb 100644
--- a/README.adoc
+++ b/README.adoc
@@ -35,10 +35,6 @@ strongly-typed, affine-typed, WASM-targeting world
 ----
 // face: jaffascript
 
-effect IO {
-  fn println(s: String) -> ();
-}
-
 function main() -{IO}-> () {
   const greeting = "Hello, JaffaScript!";
   println(greeting);
diff --git a/examples/hello.affine b/examples/hello.affine
index 43d00fe..73f6ead 100644
--- a/examples/hello.affine
+++ b/examples/hello.affine
@@ -5,10 +5,11 @@
 // `const`/`let` bindings (let lowers to let mut), brace-delimited
 // blocks, `===` equality.
 // face: jaffascript
-
-effect IO {
-  fn println(s: String) -> ();
-}
+//
+// `println` is the AffineScript builtin, which already carries the `IO`
+// effect. Do not declare `effect IO { fn println … }` here: a declared
+// effect shadows the builtin, and `eval` then stops with
+// "Unhandled effect: println" because nothing handles it.
 
 function main() -{IO}-> () {
   const greeting = "Hello, JaffaScript!";