Replace persistent variable system

Previous system linked the variable name with the saved value, meaning the variable could not be renamed or moved outside the global scope.

Instead we propose to store all persistent values in a global table, identifying each by a key. To still allow nice manipulation with identifiers, the alias syntax replace the persistent syntax for symbols - an aliases symbol will act as if a function call was used in place of the identifier when it appear.

ast/ArgumentTuple.lua

@@ -98,6 +98,21 @@ ArgumentTuple = ast.abstract.Node {
 		end
 		return r
 	end,
+	-- recreate new argumenttuple with an assignment argument added
+	with_assignment = function(self, assignment)
+		local r = ArgumentTuple:new()
+		for i=1, self.arity do
+			if self.positional[i] then
+				r:add_positional(self.positional[i])
+			elseif self.named[i] then
+				r:add_named(Identifier:new(self.named[i]), self.named[self.named[i]])
+			else
+				r:add_assignment(self.assignment) -- welp it'll error below anyway
+			end
+		end
+		r:add_assignment(assignment)
+		return r
+	end,
 
 	-- return specificity (>=0), secondary specificity (>=0)
 	-- return false, failure message

ast/Definition.lua

@@ -30,12 +30,16 @@ local Definition = ast.abstract.Node {
 		end
 
 		local symbol = self.symbol:eval(state)
-		local val = self.expression:eval(state)
-
-		if Overloadable:issub(val) then
-			state.scope:define_overloadable(symbol, val)
+		if symbol.alias then
+			state.scope:define_alias(symbol, self.expression)
 		else
-			state.scope:define(symbol, val)
+			local val = self.expression:eval(state)
+
+			if Overloadable:issub(val) then
+				state.scope:define_overloadable(symbol, val)
+			else
+				state.scope:define(symbol, val)
+			end
 		end
 
 		return Nil:new()
@@ -46,7 +50,9 @@ local Definition = ast.abstract.Node {
 		symbol:prepare(state)
 		val:prepare(state)
 
-		if Overloadable:issub(val) then
+		if self.symbol.alias then
+			state.scope:define(symbol:with{ alias = false }, val) -- disable alias to avoid call in Identifier:_prepare
+		elseif Overloadable:issub(val) then
 			state.scope:define_overloadable(symbol, val)
 		else
 			state.scope:define(symbol, val)

ast/Environment.lua

@@ -16,7 +16,11 @@ local VariableMetadata = ast.abstract.Runtime {
 		self.branched = Branched:new(state, value)
 	end,
 	get = function(self, state)
-		return self.branched:get(state)
+		if self.symbol.alias then
+			return self.branched:get(state):call(state, ArgumentTuple:new())
+		else
+			return self.branched:get(state)
+		end
 	end,
 	set = function(self, state, value)
 		assert(not self.symbol.constant, ("trying to change the value of constant %s"):format(self.symbol.string))
@@ -24,7 +28,13 @@ local VariableMetadata = ast.abstract.Runtime {
 			local r = self.symbol.type_check:call(state, ArgumentTuple:new(value))
 			if not r:truthy() then error(("type check failure for %s; %s does not satisfy %s"):format(self.symbol.string, value, self.symbol.type_check)) end
 		end
-		self.branched:set(state, value)
+		if self.symbol.alias then
+			local assign_args = ArgumentTuple:new()
+			assign_args:add_assignment(value)
+			self.branched:get(state):call(state, assign_args)
+		else
+			self.branched:set(state, value)
+		end
 	end,
 
 	_format = function(self, ...)
@@ -108,6 +118,19 @@ local Environment = ast.abstract.Runtime {
 			self:define(state, symbol, exp)
 		end
 	end,
+	define_alias = function(self, state, symbol, call)
+		assert(symbol.alias, "symbol is not an alias")
+		assert(call.type == "call", "alias expression must be a call")
+
+		local get = ast.Function:new(ast.ParameterTuple:new(), call):eval(state)
+
+		local set_param = ast.ParameterTuple:new()
+		set_param:insert_assignment(ast.FunctionParameter:new(ast.Identifier:new("value")))
+		local assign_expr = ast.Call:new(call.func, call.arguments:with_assignment(ast.Identifier:new("value")))
+		local set = ast.Function:new(set_param, assign_expr):eval(state)
+
+		self:define(state, symbol, ast.Overload:new(get, set))
+	end,
 
 	-- returns bool if variable defined in current or parent environment
 	defined = function(self, state, identifier)
@@ -156,17 +179,6 @@ local Environment = ast.abstract.Runtime {
 		return self:_get_variable(state, identifier):set(state, val)
 	end,
 
-	-- returns a list {[symbol]=val,...} of all persistent variables in the current strict layer
-	list_persistent = function(self, state)
-		assert(self.export, "not an export scope layer")
-		local r = {}
-		for _, vm in self.variables:iter(state) do
-			if vm.symbol.persistent then
-				r[vm.symbol] = vm:get(state)
-			end
-		end
-		return r
-	end,
 	-- returns a list {[symbol]=val,...} of all exported variables in the current strict layer
 	list_exported = function(self, state)
 		assert(self.export, "not an export scope layer")

ast/Symbol.lua

@@ -11,8 +11,8 @@ Symbol = ast.abstract.Node {
 	constant = nil, -- bool
 	type_check = nil, -- exp
 
+	alias = nil, -- bool
 	exported = nil, -- bool
-	persistent = nil, -- bool, imply exported
 
 	confined_to_branch = nil, -- bool
 
@@ -20,23 +20,29 @@ Symbol = ast.abstract.Node {
 		modifiers = modifiers or {}
 		self.string = str
 		self.constant = modifiers.constant
-		self.persistent = modifiers.persistent
 		self.type_check = modifiers.type_check
+		self.alias = modifiers.alias
 		self.confined_to_branch = modifiers.confined_to_branch
-		self.exported = modifiers.exported or modifiers.persistent
+		self.exported = modifiers.exported
 		if self.type_check then
 			self.format_priority = operator_priority["_::_"]
 		end
 	end,
 
 	_eval = function(self, state)
-		return Symbol:new(self.string, {
-			constant = self.constant,
-			persistent = self.persistent,
-			type_check = self.type_check and self.type_check:eval(state),
-			confined_to_branch = self.confined_to_branch,
-			exported = self.exported
-		})
+		return self:with {
+			type_check = self.type_check and self.type_check:eval(state)
+		}
+	end,
+
+	with = function(self, modifiers)
+		modifiers = modifiers or {}
+		for _, k in ipairs{"constant", "type_check", "alias", "exported", "confined_to_branch"} do
+			if modifiers[k] == nil then
+				modifiers[k] = self[k]
+			end
+		end
+		return Symbol:new(self.string, modifiers)
 	end,
 
 	_hash = function(self)
@@ -48,7 +54,7 @@ Symbol = ast.abstract.Node {
 		if self.constant then
 			s = s .. ":"
 		end
-		if self.persistent then
+		if self.alias then
 			s = s .. "&"
 		end
 		if self.exported then

ast/abstract/Node.lua

@@ -85,6 +85,7 @@ Node = class {
 		local s, r = pcall(self._eval, self, state)
 		if s then
 			r._evaluated = true
+			r:set_source(self.source)
 			return r
 		else
 			error(format_error(state, self, r), 0)

parser/expression/primary/function_definition.lua

@@ -167,11 +167,11 @@ return primary {
 		local mod_const, mod_exported, rem = source:consume(str:match("^(%:(:?)([&@]?)%$)(.-)$"))
 
 		-- get modifiers
-		local constant, exported, persistent
+		local constant, exported, alias
 		if mod_const == ":" then constant = true end
 		if mod_exported == "@" then exported = true
-		elseif mod_exported == "&" then persistent = true end
-		local modifiers = { constant = constant, exported = exported, persistent = persistent }
+		elseif mod_exported == "&" then alias = true end
+		local modifiers = { constant = constant, exported = exported, alias = alias }
 
 		-- search for a valid signature
 		local symbol, parameters

parser/expression/primary/symbol.lua

@@ -16,11 +16,11 @@ return primary {
 
 	parse = function(self, source, str)
 		local mod_const, mod_export, rem = source:consume(str:match("^(%:(:?)([&@]?))(.-)$"))
-		local constant, persistent, type_check_exp, exported
+		local constant, alias, type_check_exp, exported
 
 		-- get modifier
 		if mod_const == ":" then constant = true end
-		if mod_export == "&" then persistent = true
+		if mod_export == "&" then alias = true
 		elseif mod_export == "@" then exported = true end
 
 		-- name
@@ -35,6 +35,6 @@ return primary {
 			type_check_exp = exp.arguments.positional[2]
 		end
 
-		return ident:to_symbol{ constant = constant, persistent = persistent, exported = exported, type_check = type_check_exp }:set_source(source), rem
+		return ident:to_symbol{ constant = constant, alias = alias, exported = exported, type_check = type_check_exp }:set_source(source), rem
 	end
 }

parser/expression/secondary/infix/assignment_call.lua

@@ -18,7 +18,7 @@ return infix {
 	end,
 
 	build_ast = function(self, left, right)
-		left.arguments:add_assignment(right)
-		return Call:new(left.func, left.arguments) -- recreate Call since we modified left.arguments
+		local args = left.arguments:with_assignment(right)
+		return Call:new(left.func, args)
 	end,
 }

state/ScopeStack.lua

@@ -74,6 +74,7 @@ local ScopeStack = class {
 	-- methods that call the associated method from the current scope, see ast.Environment for details
 	define = function(self, symbol, exp) self.current:define(self.state, symbol, exp) end,
 	define_overloadable = function(self, symbol, exp) return self.current:define_overloadable(self.state, symbol, exp) end,
+	define_alias = function(self, symbol, exp) return self.current:define_alias(self.state, symbol, exp) end,
 	defined = function(self, identifier) return self.current:defined(self.state, identifier) end,
 	defined_in_current = function(self, symbol) return self.current:defined_in_current(self.state, symbol) end,
 	set = function(self, identifier, exp) self.current:set(self.state, identifier, exp) end,
@@ -140,12 +141,6 @@ local ScopeStack = class {
 		return self.current
 	end,
 
-	-- return a table { [symbol] = value } of persistent variables defined on the root scope on this branch
-	list_persistent_global = function(self)
-		local env = self.stack[1]
-		return env:list_persistent(self.state)
-	end,
-
 	_debug_state = function(self, filter)
 		filter = filter or ""
 		local s = "current branch id: "..self.state.branch_id.."\n"

state/State.lua

@@ -6,6 +6,7 @@ local ScopeStack = require("state.ScopeStack")
 local tag_manager = require("state.tag_manager")
 local event_manager = require("state.event_manager")
 local translation_manager = require("state.translation_manager")
+local persistent_manager = require("state.persistent_manager")
 local uuid = require("common").uuid
 local parser = require("parser")
 local binser = require("lib.binser")
@@ -30,6 +31,7 @@ State = class {
 
 			event_manager:setup(self)
 			tag_manager:setup(self)
+			persistent_manager:setup(self)
 			translation_manager:setup(self)
 		end
 	end,
@@ -93,28 +95,22 @@ State = class {
 
 	---## Saving and loading persistent variables
 
-	--- Return a serialized (string) representation of all global persistent variables in this State.
+	--- Return a serialized (string) representation of all persistent variables in this State.
 	--
 	-- This can be loaded back later using `:load`.
 	save = function(self)
-		local list = self.scope:list_persistent_global()
-		return binser.serialize(anselme.versions.save, list)
+		local struct = persistent_manager:capture(self)
+		return binser.serialize(anselme.versions.save, struct)
 	end,
 	--- Load a string generated by `:save`.
 	--
-	-- Variables that do not exist currently in the global scope will be defined, those that do will be overwritten with the loaded data.
+	-- Variables that already exist will be overwritten with the loaded data.
 	load = function(self, save)
-		local version, list = binser.deserializeN(save, 2)
+		local version, struct = binser.deserializeN(save, 2)
 		if version ~= anselme.versions.save then print("Loading a save file generated by a different Anselme version, things may break!") end
-		self.scope:push_global()
-		for sym, val in pairs(list) do
-			if self.scope:defined_in_current(sym) then
-				self.scope:set(sym:to_identifier(), val)
-			else
-				self.scope:define(sym, val)
-			end
+		for key, val in struct:iter() do
+			persistent_manager:set(self, key, val)
 		end
-		self.scope:pop()
 	end,
 
 	---## Current script state

state/persistent_manager.lua

@@ -0,0 +1,47 @@
+local class = require("class")
+
+local ast = require("ast")
+local Table, Identifier
+
+local persistent_identifier, persistent_symbol
+
+local persistent_manager = class {
+	init = false,
+
+	setup = function(self, state)
+		state.scope:define(persistent_symbol, Table:new(state))
+	end,
+
+	-- set the persistant variable `key` to `value` (evaluated)
+	set = function(self, state, key, value)
+		local persistent = state.scope:get(persistent_identifier)
+		persistent:set(state, key, value)
+	end,
+	-- get the persistant variable `key`'s value
+	-- if `default` is given, will set the variable to this if not currently set
+	get = function(self, state, key, default)
+		local persistent = state.scope:get(persistent_identifier)
+		if not persistent:has(state, key) then
+			if default then
+				persistent:set(state, key, default)
+			else
+				error("persistent key does not exist")
+			end
+		end
+		return persistent:get(state, key)
+	end,
+
+	-- returns a struct of the current persisted variables
+	capture = function(self, state)
+		local persistent = state.scope:get(persistent_identifier)
+		return persistent:to_struct(state)
+	end
+}
+
+package.loaded[...] = persistent_manager
+Table, Identifier = ast.Table, ast.Identifier
+
+persistent_identifier = Identifier:new("_persistent") -- Table of { [key] = Call, ... }
+persistent_symbol = persistent_identifier:to_symbol()
+
+return persistent_manager

stdlib/init.lua

@@ -31,6 +31,7 @@ return function(main_state)
 		"text",
 		"structures",
 		"closure",
-		"checkpoint"
+		"checkpoint",
+		"persist",
 	})
 end

stdlib/persist.lua

@@ -0,0 +1,32 @@
+local ast = require("ast")
+
+local persistent_manager = require("state.persistent_manager")
+
+return {
+	{
+		"persist", "(key, default)",
+		function(state, key, default)
+			return persistent_manager:get(state, key, default)
+		end
+	},
+	{
+		"persist", "(key, default) = value",
+		function(state, key, default, value)
+			persistent_manager:set(state, key, value)
+			return ast.Nil:new()
+		end
+	},
+	{
+		"persist", "(key)",
+		function(state, key)
+			return persistent_manager:get(state, key)
+		end
+	},
+	{
+		"persist", "(key) = value",
+		function(state, key, value)
+			persistent_manager:set(state, key, value)
+			return ast.Nil:new()
+		end
+	},
+}