Undefine _ in attached block

anselme/ast/Environment.lua

@@ -68,6 +68,7 @@ local Environment = ast.abstract.Runtime {
 	variables = nil, -- Table of { {identifier} = variable metadata, ... }
 
 	partial = nil, -- { [name string] = true, ... }
+	undefine = nil, -- { [name string] = true, ... }
 	export = nil, -- bool
 
 	init = function(self, state, parent, partial_names, is_export)
@@ -75,6 +76,7 @@ local Environment = ast.abstract.Runtime {
 		self.parent = parent
 		self.partial = partial_names
 		self.export = is_export
+		self.undefine = {}
 	end,
 
 	traverse = function(self, fn, ...)
@@ -97,7 +99,11 @@ local Environment = ast.abstract.Runtime {
 			or (self.export ~= symbol.exported) then
 			return self.parent:define(state, symbol, exp)
 		end
-		self.variables:set(state, symbol:to_identifier(), VariableMetadata:new(state, symbol, exp))
+		if symbol.undefine then
+			self.undefine[name] = true
+		else
+			self.variables:set(state, symbol:to_identifier(), VariableMetadata:new(state, symbol, exp))
+		end
 	end,
 	-- define or redefine new overloadable variable in current environment, inheriting existing overload variants from (parent) scopes
 	define_overloadable = function(self, state, symbol, exp)
@@ -132,7 +138,7 @@ local Environment = ast.abstract.Runtime {
 	defined = function(self, state, identifier)
 		if self.variables:has(state, identifier) then
 			return true
-		elseif self.parent then
+		elseif self.parent and not self.undefine[identifier.name] then
 			return self.parent:defined(state, identifier)
 		end
 		return false
@@ -143,9 +149,10 @@ local Environment = ast.abstract.Runtime {
 		local name = symbol.string
 		if self.variables:has(state, symbol:to_identifier()) then
 			return true
-		elseif (self.partial and not self.partial[name])
-			or (self.export ~= symbol.exported) then
-			return self.parent:defined_in_current(state, symbol)
+		elseif self.parent and not self.undefine[name] then
+			if (self.partial and not self.partial[name]) or (self.export ~= symbol.exported) then
+				return self.parent:defined_in_current(state, symbol)
+			end
 		end
 		return false
 	end,
@@ -159,7 +166,7 @@ local Environment = ast.abstract.Runtime {
 		if self:defined(state, identifier) then
 			if self.variables:has(state, identifier) then
 				return self.variables:get(state, identifier)
-			elseif self.parent then
+			elseif self.parent and not self.undefine[identifier.name] then
 				return self.parent:_get_variable(state, identifier)
 			end
 		else

anselme/ast/PartialScope.lua

@@ -1,7 +1,7 @@
 -- create a partial layer to define temporary variables
 
 local ast = require("anselme.ast")
-local Identifier, Quote
+local Identifier, Quote, Nil
 
 local attached_block_identifier, attached_block_symbol
 local unpack = table.unpack or unpack
@@ -11,7 +11,7 @@ PartialScope = ast.abstract.Node {
 	type = "partial scope",
 
 	expression = nil,
-	definitions = nil, -- {[sym]=value,...} where values are already evaluated!
+	definitions = nil, -- {[sym]=value,...}
 	_identifiers = nil, -- {identifier,...} - just a cache so we don't rebuild it on every eval
 
 	init = function(self, expression)
@@ -49,7 +49,7 @@ PartialScope = ast.abstract.Node {
 
 	_eval = function(self, state)
 		state.scope:push_partial(unpack(self._identifiers))
-		for sym, val in pairs(self.definitions) do state.scope:define(sym, val) end
+		for sym, val in pairs(self.definitions) do state.scope:define(sym:eval(state), val:eval(state)) end
 		local exp = self.expression:eval(state)
 		state.scope:pop()
 
@@ -71,14 +71,16 @@ PartialScope = ast.abstract.Node {
 	end,
 	-- class method: return a PartialScope that define the block identifier _ to a Quote of `block`
 	attach_block = function(self, expression, block)
-		local partial = ast.PartialScope:new(expression)
-		partial:define(attached_block_symbol, Quote:new(block))
+		local partial = PartialScope:new(expression)
+		local unpartial = PartialScope:new(block)
+		unpartial:define(attached_block_symbol:with{undefine=true}, Nil:new())
+		partial:define(attached_block_symbol, Quote:new(unpartial))
 		return partial
 	end
 }
 
 package.loaded[...] = PartialScope
-Identifier, Quote = ast.Identifier, ast.Quote
+Identifier, Quote, Nil = ast.Identifier, ast.Quote, ast.Nil
 
 attached_block_identifier = Identifier:new("_")
 attached_block_symbol = attached_block_identifier:to_symbol()

anselme/ast/Symbol.lua

@@ -15,6 +15,7 @@ Symbol = ast.abstract.Node {
 	exported = nil, -- bool
 
 	confined_to_branch = nil, -- bool
+	undefine = nil, -- bool
 
 	init = function(self, str, modifiers)
 		modifiers = modifiers or {}
@@ -24,6 +25,7 @@ Symbol = ast.abstract.Node {
 		self.alias = modifiers.alias
 		self.confined_to_branch = modifiers.confined_to_branch
 		self.exported = modifiers.exported
+		self.undefine = modifiers.undefine
 	end,
 
 	_eval = function(self, state)
@@ -34,7 +36,7 @@ Symbol = ast.abstract.Node {
 
 	with = function(self, modifiers)
 		modifiers = modifiers or {}
-		for _, k in ipairs{"constant", "type_check", "alias", "exported", "confined_to_branch"} do
+		for _, k in ipairs{"constant", "type_check", "alias", "exported", "confined_to_branch", "undefine"} do
 			if modifiers[k] == nil then
 				modifiers[k] = self[k]
 			end

anselme/stdlib/closure.lua

@@ -4,6 +4,8 @@ local assert0 = require("anselme.common").assert0
 
 local calling_environment_manager = require("anselme.state.calling_environment_manager")
 
+local block_identifier = Identifier:new("_")
+
 return {
 	{
 		"defined", "(c::function, s::string)",
@@ -88,21 +90,33 @@ return {
 		end
 	},
 	{
-		"attached block", "(level::number=1)",
-		function(state, level)
+		"attached block", "(level::number=1, keep return=false)",
+		function(state, level, keep_return)
 			-- level 2: env of the function that called the function that called attached block
 			local env = calling_environment_manager:get_level(state, level:to_lua(state)+1)
-			local r = env:get(state, Identifier:new("_"))
-			return Function:with_return_boundary(ParameterTuple:new(), r.expression):eval(state)
+			local r = env:get(state, block_identifier)
+			if keep_return:truthy() then
+				return Function:new(ParameterTuple:new(), r.expression):eval(state)
+			else
+				return Function:with_return_boundary(ParameterTuple:new(), r.expression):eval(state)
+			end
 		end
 	},
 	{
-		"attached block keep return", "(level::number=1)",
-		function(state, level)
+		"attached block", "(level::number=1, keep return=false, default)",
+		function(state, level, keep_return, default)
 			-- level 2: env of the function that called the function that called attached block
 			local env = calling_environment_manager:get_level(state, level:to_lua(state)+1)
-			local r = env:get(state, Identifier:new("_"))
-			return Function:new(ParameterTuple:new(), r.expression):eval(state)
+			if env:defined(state, block_identifier) then
+				local r = env:get(state, block_identifier)
+				if keep_return:truthy() then
+					return Function:new(ParameterTuple:new(), r.expression):eval(state)
+				else
+					return Function:with_return_boundary(ParameterTuple:new(), r.expression):eval(state)
+				end
+			else
+				return default
+			end
 		end
 	},
 }

anselme/stdlib/conditionals.lua

@@ -18,7 +18,7 @@ end
 
 return {
 	{
-		"if", "(condition, expression=attached block keep return!)", function(state, condition, expression)
+		"if", "(condition, expression=attached block(keep return=true))", function(state, condition, expression)
 			ensure_if_variable(state)
 			if condition:truthy() or expression:contains_current_resume_target(state) then
 				set_if_variable(state, true)
@@ -42,7 +42,7 @@ return {
 		end
 	},
 	{
-		"else if", "(condition, expression=attached block keep return!)",
+		"else if", "(condition, expression=attached block(keep return=true))",
 		function(state, condition, expression)
 			ensure_if_variable(state)
 			if (not last_if_success(state) and condition:truthy()) or expression:contains_current_resume_target(state) then
@@ -55,7 +55,7 @@ return {
 		end
 	},
 	{
-		"else", "(expression=attached block keep return!)",
+		"else", "(expression=attached block(keep return=true))",
 		function(state, expression)
 			ensure_if_variable(state)
 			if not last_if_success(state) or expression:contains_current_resume_target(state) then
@@ -67,7 +67,7 @@ return {
 		end
 	},
 	{
-		"while", "(condition, expression=attached block keep return!)",
+		"while", "(condition, expression=attached block(keep return=true))",
 		function(state, condition, expression)
 			ensure_if_variable(state)
 			local cond = condition:call(state, ArgumentTuple:new())

anselme/stdlib/script_script.lua

@@ -8,18 +8,19 @@ return [[
 
 	fn.:check = $(anchor::anchor)
 		fn.reached(anchor) = (fn.reached(anchor) | 0) + 1
-	fn.:checkpoint = $(anchor::anchor)
-		fn.current checkpoint = anchor
-		if(resumed from != anchor)
-			fn.reached(anchor) = (fn.reached(anchor) | 0) + 1
-			merge branch!
-	fn.:checkpoint = $(anchor::anchor, on resume::function)
-		fn.current checkpoint = anchor
-		if(resumed from == anchor | resuming(2))
-			on resume!
+	fn.:checkpoint = $(anchor::anchor, on resume=attached block(default=()))
+		if(on resume)
+			fn.current checkpoint = anchor
+			if(resumed from == anchor | resuming(4))
+				on resume!
+			else!
+				fn.reached(anchor) = (fn.reached(anchor) | 0) + 1
+				merge branch!
 		else!
-			fn.reached(anchor) = (fn.reached(anchor) | 0) + 1
-			merge branch!
+			fn.current checkpoint = anchor
+			if(resumed from != anchor)
+				fn.reached(anchor) = (fn.reached(anchor) | 0) + 1
+				merge branch!
 
 	:f = $
 		if(fn.current checkpoint)