Add nil expression and fix return behavior with nil expression

README.md

@@ -255,7 +255,7 @@ Paragraphs always have the following variable defined in its namespace by defaul
 :42 foo
 ```
 
-* `@`: return line. Can be followed by an [expression](#expressions). Exit the current function and returns the expression's value.
+* `@`: return line. Can be followed by an [expression](#expressions); otherwise nil expression is assumed. Exit the current function and returns the expression's value.
 
 ```
 $ hey
@@ -417,7 +417,7 @@ Note that these are *not* Lua expressions.
 
 Default types are:
 
-* `nil`: nil.
+* `nil`: nil. Can be defined using empty parantheses `()`.
 
 * `number`: a number. Can be defined similarly to Lua number literals.
 

interpreter/expression.lua

@@ -9,8 +9,14 @@ local unpack = table.unpack or unpack
 -- returns evaluated value if success
 -- returns nil, error if error
 local function eval(state, exp)
+	-- nil
+	if exp.type == "nil" then
+		return {
+			type = "nil",
+			value = nil
+		}
 	-- number
-	if exp.type == "number" then
+	elseif exp.type == "number" then
 		return {
 			type = "number",
 			value = exp.value

interpreter/interpreter.lua

@@ -95,11 +95,8 @@ local function run_line(state, line)
 			if e then return v, e end
 			if v then return v end
 		elseif line.type == "return" then
-			local v, e
-			if line.expression then
-				v, e = eval(state, line.expression)
-				if not v then return v, ("%s; at %s"):format(e, line.source) end
-			end
+			local v, e = eval(state, line.expression)
+			if not v then return v, ("%s; at %s"):format(e, line.source) end
 			return v
 		elseif line.type == "text" then
 			local t, er = eval_text(state, line.text)

parser/expression.lua

@@ -63,9 +63,15 @@ local function expression(s, state, namespace, currentPriority, operatingOn)
 		elseif s:match("^%b()") then
 			local content, r = s:match("^(%b())(.*)$")
 			content = content:gsub("^%(", ""):gsub("%)$", "")
-			local exp, r_paren = expression(content, state, namespace)
-			if not exp then return nil, "invalid expression inside parentheses: "..r_paren end
-			if r_paren:match("[^%s]") then return nil, ("unexpected %q at end of parenthesis expression"):format(r_paren) end
+			local exp
+			if content:match("[^%s]") then
+				local r_paren
+				exp, r_paren = expression(content, state, namespace)
+				if not exp then return nil, "invalid expression inside parentheses: "..r_paren end
+				if r_paren:match("[^%s]") then return nil, ("unexpected %q at end of parenthesis expression"):format(r_paren) end
+			else
+				exp = { type = "nil", return_type = "nil", value = nil }
+			end
 			return expression(r, state, namespace, currentPriority, {
 				type = "parentheses",
 				return_type = exp.return_type,

parser/postparser.lua

@@ -29,14 +29,10 @@ local function parse(state)
 		end
 		-- expressions
 		if line.expression then
-			if line.expression:match("[^%s]") then
-				local exp, rem = expression(line.expression, state, namespace)
-				if not exp then return nil, ("%s; at %s"):format(rem, line.source) end
-				if rem:match("[^%s]") then return nil, ("expected end of expression before %q; at %s"):format(rem, line.source) end
-				line.expression = exp
-			else
-				line.expression = nil
-			end
+			local exp, rem = expression(line.expression, state, namespace)
+			if not exp then return nil, ("%s; at %s"):format(rem, line.source) end
+			if rem:match("[^%s]") then return nil, ("expected end of expression before %q; at %s"):format(rem, line.source) end
+			line.expression = exp
 			-- function return type information
 			if line.type == "return" then
 				local variant = line.parent_function.variant

parser/preparser.lua

@@ -303,12 +303,22 @@ local function parse_line(line, state, namespace)
 	elseif l:match("^%#") then
 		r.type = "tag"
 		r.child = true
-		r.expression = l:match("^%#(.*)$")
+		local expr = l:match("^%#(.*)$")
+		if expr:match("[^%s]") then
+			r.expression = expr
+		else
+			r.expression = nil
+		end
 	-- return
 	elseif l:match("^%@") then
 		r.type = "return"
 		r.parent_function = true
-		r.expression = l:match("^%@(.*)$")
+		local expr = l:match("^%@(.*)$")
+		if expr:match("[^%s]") then
+			r.expression = expr
+		else
+			r.expression = "()"
+		end
 	-- text
 	elseif l:match("[^%s]") then
 		r.type = "text"

test/tests/function return exit function nested.ans

@@ -0,0 +1,9 @@
+$ hey
+	§ foo
+		@2
+		@3
+	@5
+	u
+
+{hey}
+{hey.foo}

test/tests/function return exit function nested.lua

@@ -0,0 +1,19 @@
+local _={}
+_[7]={}
+_[6]={}
+_[5]={data="2",tags=_[7]}
+_[4]={data="5",tags=_[6]}
+_[3]={_[4],_[5]}
+_[2]={"return"}
+_[1]={"text",_[3]}
+return {_[1],_[2]}
+--[[
+{ "text", { {
+      data = "5",
+      tags = {}
+    }, {
+      data = "2",
+      tags = {}
+    } } }
+{ "return" }
+]]--

test/tests/function return exit function.ans

@@ -0,0 +1,6 @@
+$ hey
+	@5
+	a
+	@2
+
+{hey}

test/tests/function return exit function.lua

@@ -0,0 +1,14 @@
+local _={}
+_[5]={}
+_[4]={data="5",tags=_[5]}
+_[3]={_[4]}
+_[2]={"return"}
+_[1]={"text",_[3]}
+return {_[1],_[2]}
+--[[
+{ "text", { {
+      data = "5",
+      tags = {}
+    } } }
+{ "return" }
+]]--