unless line decorator

moonscript/parse.lua

@@ -179,7 +179,7 @@ local function flatten_func(callee, args)
 	return {"chain", callee, args}
 end
 
--- wraps a statement that has a line decorator
+-- transforms a statement that has a line decorator
 local function wrap_decorator(stm, dec)
 	if not dec then return stm end
 
@@ -189,6 +189,12 @@ local function wrap_decorator(stm, dec)
 		local _, cond, fail = unpack(dec)
 		if fail then fail = {"else", {fail}} end
 		stm = {"if", cond, {stm}, fail}
+	elseif dec[1] == "unless" then
+		stm = {
+			"if",
+			{"not", {"parens", dec[2]}},
+			{stm}
+		}
 	elseif dec[1] == "comprehension" then
 		local _, clauses = unpack(dec)
 		stm = {"comprehension", stm, clauses}
@@ -288,6 +294,7 @@ local build_grammar = wrap_env(function()
 			) * Space * ((
 				-- statement decorators
 				key"if" * Exp * (key"else" * Exp)^-1 * Space / mark"if" +
+				key"unless" * Exp / mark"unless" +
 				CompInner / mark"comprehension"
 			) * Space)^-1 / wrap_decorator,
 

tests/inputs/syntax.moon

@@ -102,6 +102,8 @@ hi = -"herfef"
 x = -[x for x in x]
 
 print "hello" if cool
+print "hello" unless cool
+print "hello" unless 1212 and 3434 -- hello
 
 print "nutjob"
 

tests/outputs/syntax.lua

@@ -101,6 +101,12 @@ end)()
 if cool then
   print("hello")
 end
+if not (cool) then
+  print("hello")
+end
+if not (1212 and 3434) then
+  print("hello")
+end
 print("nutjob")
 if hello then
   _ = 343