From 464121c5b7092f2521d21be390b01173e28fbd00 Mon Sep 17 00:00:00 2001
From: Matthew Wild <mwild1@gmail.com>
Date: Sun, 30 Dec 2018 12:55:58 +0000
Subject: util.error: Add new util library for structured errors

---
 util/error.lua | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 util/error.lua

diff --git a/util/error.lua b/util/error.lua
new file mode 100644
index 00000000..ed61793f
--- /dev/null
+++ b/util/error.lua
@@ -0,0 +1,40 @@
+local error_mt = { __name = "error" };
+
+function error_mt:__tostring()
+	return ("error<%s:%s:%s>"):format(self.type, self.condition, self.text);
+end
+
+local function is_err(e)
+	return getmetatable(e) == error_mt;
+end
+
+local function new(e, context, registry)
+	local template = (registry and registry[e]) or e or {};
+	return setmetatable({
+		type = template.type or "cancel";
+		condition = template.condition or "undefined-condition";
+		text = template.text;
+
+		context = context or template.context or { _error_id = e };
+	}, error_mt);
+end
+
+local function coerce(ok, err, ...)
+	if ok or is_err(err) then
+		return ok, err, ...;
+	end
+
+	local new_err = setmetatable({
+		native = err;
+
+		type = "cancel";
+		condition = "undefined-condition";
+	}, error_mt);
+	return ok, new_err, ...;
+end
+
+return {
+	new = new;
+	coerce = coerce;
+	is_err = is_err;
+}
-- 
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