fix compile failure when comprehension exp has no value

moonscript/transform.lua

@@ -5,10 +5,6 @@ local data = require("moonscript.data")
 local reversed = util.reversed
 local ntype, build, smart_node, is_slice = types.ntype, types.build, types.smart_node, types.is_slice
 local insert = table.insert
-local is_value
-is_value = function(stm)
-  return moonscript.compile.Block:is_value(stm) or Value:can_transform(stm)
-end
 NameProxy = (function()
   local _parent_0 = nil
   local _base_0 = {
@@ -241,7 +237,7 @@ Statement = Transformer({
     if #values == 1 and types.cascading[ntype(values[1])] then
       values[1] = self.transform.statement(values[1], function(stm)
         local t = ntype(stm)
-        if is_value(stm) then
+        if types.is_value(stm) then
           return {
             "assign",
             names,
@@ -843,15 +839,19 @@ implicitly_return = function(scope)
   local fn
   fn = function(stm)
     local t = ntype(stm)
-    if types.manual_return[t] or not is_value(stm) then
+    if types.manual_return[t] or not types.is_value(stm) then
       return stm
     elseif types.cascading[t] then
       return scope.transform.statement(stm, fn)
     else
-      return {
-        "return",
-        stm
-      }
+      if t == "comprehension" and not types.comprehension_has_value(stm) then
+        return stm
+      else
+        return {
+          "return",
+          stm
+        }
+      end
     end
   end
   return fn

moonscript/transform.moon

@@ -11,10 +11,6 @@ import insert from table
 
 export Statement, Value, NameProxy, Run
 
--- TODO refactor
-is_value = (stm) ->
-  moonscript.compile.Block\is_value(stm) or Value\can_transform stm
-
 class NameProxy
   new: (@prefix) =>
     self[1] = "temp_name"
@@ -131,7 +127,7 @@ Statement = Transformer {
     if #values == 1 and types.cascading[ntype values[1]]
       values[1] = @transform.statement values[1], (stm) ->
         t = ntype stm
-        if is_value stm
+        if types.is_value stm
           {"assign", names, {stm}}
         else
           stm
@@ -201,6 +197,7 @@ Statement = Transformer {
 
   comprehension: (node, action) =>
     _, exp, clauses = unpack node
+
     action = action or (exp) -> {exp}
     construct_comprehension action(exp), clauses
 
@@ -470,12 +467,15 @@ default_accumulator = (node) =>
 implicitly_return = (scope) ->
   fn = (stm) ->
     t = ntype stm
-    if types.manual_return[t] or not is_value stm
+    if types.manual_return[t] or not types.is_value stm
       stm
     elseif types.cascading[t]
       scope.transform.statement stm, fn
     else
-      {"return", stm}
+      if t == "comprehension" and not types.comprehension_has_value stm
+        stm
+      else
+        {"return", stm}
 
   fn
 

moonscript/types.lua

@@ -13,6 +13,13 @@ cascading = data.Set({
   "with",
   "switch"
 })
+is_value = function(stm)
+  local compile, transform = moonscript.compile, moonscript.transform
+  return compile.Block:is_value(stm) or transform.Value:can_transform(stm)
+end
+comprehension_has_value = function(comp)
+  return is_value(comp[2])
+end
 ntype = function(node)
   if type(node) ~= "table" then
     return "value"

moonscript/types.moon

@@ -2,8 +2,9 @@ module "moonscript.types", package.seeall
 util = require "moonscript.util"
 data = require "moonscript.data"
 
-export ntype, smart_node, build
+export ntype, smart_node, build, is_value
 export is_slice, manual_return, cascading
+export comprehension_has_value
 
 import insert from table
 
@@ -13,6 +14,13 @@ manual_return = data.Set{"foreach", "for", "while", "return"}
 -- assigns and returns are bubbled into their bodies
 cascading = data.Set{ "if", "with", "switch" }
 
+is_value = (stm) ->
+  import compile, transform from moonscript
+  compile.Block\is_value(stm) or transform.Value\can_transform stm
+
+comprehension_has_value = (comp) ->
+  is_value comp[2]
+
 -- type of node as string
 ntype = (node) ->
   if type(node) != "table"

tests/inputs/lists.moon

@@ -69,4 +69,5 @@ normal = (hello) ->
 test = x 1,2,3,4,5
 print thing for thing in *test
 
+-> a = b for row in *rows
 

tests/outputs/lists.lua

@@ -270,4 +270,12 @@ local _list_8 = test
 for _index_0 = 1, #_list_8 do
   local thing = _list_8[_index_0]
   print(thing)
+end
+local _
+_ = function()
+  local _list_9 = rows
+  for _index_0 = 1, #_list_9 do
+    local row = _list_9[_index_0]
+    a = b
+  end
 end