From 309258abbea7ca7a8ba1d4d254ec26f001a76d77 Mon Sep 17 00:00:00 2001
From: timofey <tim@ongoteam.yaconnect.com>
Date: Sat, 20 May 2023 12:09:09 +0000
Subject: [PATCH] s01-fail.md

---
 src/SUMMARY.md           |  1 +
 src/ch04/s00-concerns.md |  3 +++
 src/ch04/s01-fail.md     | 16 ++++++++++++++++
 3 files changed, 20 insertions(+)
 create mode 100644 src/ch04/s01-fail.md

diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index 4201ee3..d2c9a95 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -6,3 +6,4 @@
 - [Implementation]()
 - [Usage]()
 - [Current Implementation Concerns](./ch04/s00-concerns.md)
+  - [Fail Semantics](./ch04/s01-fail.md)
diff --git a/src/ch04/s00-concerns.md b/src/ch04/s00-concerns.md
index 783f192..e3b7738 100644
--- a/src/ch04/s00-concerns.md
+++ b/src/ch04/s00-concerns.md
@@ -9,3 +9,6 @@
 * Prevents using varied hash sizes.
   * Prevents using dynamic hash sizes.
 * Not a context-specific constant because associated `const`s in `const` context are unstable.
+
+## `Fail`/`FailMonad`/etc. have unclear semantics
+See the [relevant subchapter](./s01-fail.md)
diff --git a/src/ch04/s01-fail.md b/src/ch04/s01-fail.md
new file mode 100644
index 0000000..790d1f9
--- /dev/null
+++ b/src/ch04/s01-fail.md
@@ -0,0 +1,16 @@
+# Fail Semantics
+
+## Lack of proper support for injecting errors into classes that are already `Fail`
+* Classes have only one implementation of `Fail` per error type.
+* Proposed solutions:
+  * Have `Fail` as a separate trait with the error and the class as associated types.
+  * `OverloadClass` to mix-in additional `Fail`.
+
+## Lack of support for strict ordering of errors
+* Current (possible) implementations of having one error or another either allow short-circuiting
+on only one of them, or give them both the same priority.
+**Right now this model is considered the main one**,
+i.e. this restriction may get stabilised and standardised at some point.
+* More complex behaviours are expected to require a more complex execution model, with states
+taking messages from other states and optionally dropping their own execution, if their
+result\['s error\] is guaranteed to be "less sever" than the error it receives.