From 633f7b2d618a8ba1b931f22be027d669fef56963 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89tienne=20Reuh=20Fildadut?= <fildadut@reuh.eu>
Date: Sat, 5 Jun 2021 22:38:02 +0200
Subject: [PATCH] Prevent from restarting interpreter after return or error

---
 anselme.lua          | 17 +++++++++++++++--
 notes.txt            |  4 +---
 stdlib/functions.lua |  1 +
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/anselme.lua b/anselme.lua
index 5b18042..c35e570 100644
--- a/anselme.lua
+++ b/anselme.lua
@@ -66,12 +66,17 @@ local interpreter_methods = {
 	state = nil,
 	-- VM this interpreter belongs to
 	vm = nil,
+	-- event that stopped the interpreter
+	end_event = nil,
 
 	--- run the VM until the next event
 	-- will merge changed variables on successful script end
-	-- returns event, data; if event is "return" or "error", the interpreter must not be stepped further
+	-- returns event, data; if event is "return" or "error", the interpreter can not be stepped further
 	step = function(self)
 		-- check status
+		if self.end_event then
+			return "error", ("interpreter can't be restarted after receiving a %s event"):format(self.end_event)
+		end
 		if coroutine.status(self.state.interpreter.coroutine) ~= "suspended" then
 			return "error", ("can't step interpreter because it has already finished or is already running (coroutine status: %s)"):format(coroutine.status(self.state.interpreter.coroutine))
 		end
@@ -96,8 +101,9 @@ local interpreter_methods = {
 		anselme.running = self
 		local success, event, data = coroutine.resume(self.state.interpreter.coroutine)
 		anselme.running = previous
-		if not success then return "error", event end
+		if not success then event, data = "error", event end
 		if event == "return" then merge_state(self.state) end
+		if event == "return" or event == "error" then self.end_event = event end
 		return event, data
 	end,
 
@@ -135,6 +141,10 @@ local interpreter_methods = {
 	--- run an expression or block: may trigger events and must be called from within the interpreter coroutine
 	-- return lua value (nil if nothing returned)
 	run = function(self, expr, namespace)
+		-- check status
+		if coroutine.status(self.state.interpreter.coroutine) ~= "running" then
+			error("run must be called from whithin the interpreter coroutine")
+		end
 		-- parse
 		local err
 		if type(expr) ~= "table" then expr, err = expression(tostring(expr), self.state.interpreter.global_state, namespace or "") end
@@ -159,6 +169,9 @@ local interpreter_methods = {
 	-- return value in case of success (nil if nothing returned)
 	-- return nil, err in case of error
 	eval = function(self, expr, namespace)
+		if self.end_event then
+			return "error", ("interpreter can't be restarted after receiving a %s event"):format(self.end_event)
+		end
 		-- parse
 		local err
 		if type(expr) ~= "table" then expr, err = expression(tostring(expr), self.state.interpreter.global_state, namespace or "") end
diff --git a/notes.txt b/notes.txt
index 6f6ab41..9b28639 100644
--- a/notes.txt
+++ b/notes.txt
@@ -43,7 +43,7 @@ Reserved symbols that are still not used as a line type: `^+-=</[]*{}|\_!?.,;)"&
 
 TODO: test reacheability of script paths
 
-TODO: redisign the checkpoint system to work better when used with parallel scripts (as they will rewrite each other's variables)
+TODO: redisign the checkpoint system to work better when used with parallel scripts (if both change the same variable, will be overwritten)
 
 TODO: redisign a static type checking system
 If we want to go full gradual typing, it would help to:
@@ -55,5 +55,3 @@ Advantages:
 Disadvantages:
 * idk if it's worth the trouble
 * could do something like `$ ()(l::list(?), i::number)::?`, but then can't return nil on not found...
-
-TODO: ensure that most stuff in the state stays consistent after an error was thrown
diff --git a/stdlib/functions.lua b/stdlib/functions.lua
index 2343e4d..56add1a 100644
--- a/stdlib/functions.lua
+++ b/stdlib/functions.lua
@@ -125,6 +125,7 @@ functions = {
 		end
 	},
 	-- alias
+	-- TODO: directly change global state, should new aliases be kept in case of interpreter error before a merge?
 	["alias(identifier::string, alias::string)"] = {
 		value = function(identifier, alias)
 			-- check identifiers