allow assignment in if condition

Author: leafo

moonscript/parse.lua

@@ -191,6 +191,15 @@ local function format_assign(lhs_exps, assign)
 	error "unknown assign expression"
 end
 
+-- the if statement only takes a single lhs, so we wrap in table to git to
+-- "assign" tuple format
+local function format_assign_for_if(lhs, assign)
+	if assign then
+		return format_assign({lhs}, assign)
+	end
+	return lhs
+end
+
 local function sym(chars)
 	return Space * chars
 end
@@ -389,7 +398,7 @@ local build_grammar = wrap_env(function()
 		SwitchCase = key"when" * Exp * key"then"^-1 * Body / mark"case",
 		SwitchElse = key"else" * Body / mark"else",
 
-		If = key"if" * Exp * key"then"^-1 * Body *
+		If = key"if" * (Exp * Assign^-1 / format_assign_for_if) * key"then"^-1 * Body *
 			((Break * CheckIndent)^-1 * EmptyLine^0 * key"elseif" * Exp * key"then"^-1 * Body / mark"elseif")^0 *
 			((Break * CheckIndent)^-1 * EmptyLine^0 * key"else" * Body / mark"else")^-1 / mark"if",
 

moonscript/transform.lua

@@ -519,9 +519,27 @@ Statement = Transformer({
     end
     return construct_comprehension(action(exp), clauses)
   end,
+  ["do"] = function(self, node, ret)
+    if ret then
+      node[2] = apply_to_last(node[2], ret)
+    end
+    return node
+  end,
   ["if"] = function(self, node, ret)
+    smart_node(node)
+    if ntype(node.cond) == "assign" then
+      local _, assign, body = unpack(node)
+      local name = assign[2][1]
+      return build["do"]({
+        assign,
+        {
+          "if",
+          name,
+          unpack(node, 3)
+        }
+      })
+    end
     if ret then
-      smart_node(node)
       node['then'] = apply_to_last(node['then'], ret)
       for i = 4, #node do
         local case = node[i]

moonscript/transform.moon

@@ -226,16 +226,31 @@ Statement = Transformer {
     action = action or (exp) -> {exp}
     construct_comprehension action(exp), clauses
 
-  -- handle cascading return decorator
+  do: (node, ret) =>
+    node[2] = apply_to_last node[2], ret if ret
+    node
+
   if: (node, ret) =>
+    smart_node node
+
+    -- extract assigns in cond
+    if ntype(node.cond) == "assign"
+      _, assign, body = unpack node
+      name = assign[2][1]
+      return build["do"] {
+        assign
+        {"if", name, unpack node, 3}
+      }
+
+    -- handle cascading return decorator
     if ret
-      smart_node node
       -- mutate all the bodies
       node['then'] = apply_to_last node['then'], ret
       for i = 4, #node
         case = node[i]
         body_idx = #node[i]
         case[body_idx] = apply_to_last case[body_idx], ret
+
     node
 
   with: (node, ret) =>

tests/inputs/cond.moon

@@ -50,4 +50,19 @@ if lets go
 elseif "just us"
   print "will smith" else show 5555555
 
+--
+
+if something = 10
+  print something
+else
+  print "else"
+
+hello = if something = 10
+  print something
+else
+  print "else"
+
+
+hello = 5 + if something = 10
+  print something
 

tests/outputs/cond.lua

@@ -84,4 +84,29 @@ elseif "just us" then
   print("will smith")
 else
   show(5555555)
-end
+end
+do
+  local something = 10
+  if something then
+    print(something)
+  else
+    print("else")
+  end
+end
+local hello
+do
+  local something = 10
+  if something then
+    hello = print(something)
+  else
+    hello = print("else")
+  end
+end
+hello = 5 + (function()
+  do
+    local something = 10
+    if something then
+      return print(something)
+    end
+  end
+end)()

todo

@@ -50,3 +50,8 @@ not working right:
 
 * let array items in table be defined without {} when indented
 
+
+* allow dot access with names that are keywords: hello.then
+
+* convert tree transformer to be depth first instead of breadth first (lazy)
+