diff --git a/moonscript/compile/line.lua b/moonscript/compile/line.lua
index a9296d1..73a63d5 100644
--- a/moonscript/compile/line.lua
+++ b/moonscript/compile/line.lua
@@ -305,44 +305,6 @@ line_compile = {
     end
     return nil
   end,
-  comprehension = function(self, node, action)
-    local _, exp, clauses = unpack(node)
-    if not action then
-      action = function(exp)
-        return {
-          exp
-        }
-      end
-    end
-    local current_stms = action(exp)
-    for _, clause in reversed(clauses) do
-      local t = clause[1]
-      if t == "for" then
-        local names, iter
-        _, names, iter = unpack(clause)
-        current_stms = {
-          "foreach",
-          names,
-          iter,
-          current_stms
-        }
-      elseif t == "when" then
-        local cond
-        _, cond = unpack(clause)
-        current_stms = {
-          "if",
-          cond,
-          current_stms
-        }
-      else
-        current_stms = error("Unknown comprehension clause: " .. t)
-      end
-      current_stms = {
-        current_stms
-      }
-    end
-    return self:stms(current_stms)
-  end,
   with = function(self, node, ret)
     local _, exp, block = unpack(node)
     do
diff --git a/moonscript/compile/line.moon b/moonscript/compile/line.moon
index 921f68a..773afce 100644
--- a/moonscript/compile/line.moon
+++ b/moonscript/compile/line.moon
@@ -167,28 +167,6 @@ line_compile =
       @declare names
     nil
 
-  comprehension: (node, action) =>
-    _, exp, clauses = unpack node
-
-    if not action
-      action = (exp) -> {exp}
-
-    current_stms = action exp
-    for _, clause in reversed clauses
-      t = clause[1]
-      current_stms = if t == "for"
-        _, names, iter = unpack clause
-        {"foreach", names, iter, current_stms}
-      elseif t == "when"
-        _, cond = unpack clause
-        {"if", cond, current_stms}
-      else
-        error "Unknown comprehension clause: "..t
-      current_stms = {current_stms}
-
-    @stms current_stms
-
-
   with: (node, ret) =>
     _, exp, block = unpack node
 
diff --git a/moonscript/compile/value.lua b/moonscript/compile/value.lua
index 1e5248f..10cf5ff 100644
--- a/moonscript/compile/value.lua
+++ b/moonscript/compile/value.lua
@@ -103,31 +103,6 @@ value_compile = {
       return _with_0
     end
   end,
-  comprehension = function(self, node)
-    local _, exp, iter = unpack(node)
-    do
-      local _with_0 = self:block()
-      local tmp_name = _with_0:init_free_var("accum", {
-        "table"
-      })
-      local len_name = _with_0:init_free_var("len", 0)
-      local action
-      action = function(value)
-        return table_append(tmp_name, len_name, value)
-      end
-      _with_0:stm(node, action)
-      _with_0:stm({
-        "return",
-        tmp_name
-      })
-      if _with_0.has_varargs then
-        _with_0.header, _with_0.footer = "(function(...)", "end)(...)"
-      else
-        _with_0.header, _with_0.footer = "(function()", "end)()"
-      end
-      return _with_0
-    end
-  end,
   chain = function(self, node)
     local callee = node[2]
     if callee == -1 then
diff --git a/moonscript/compile/value.moon b/moonscript/compile/value.moon
index d7ed0b0..0828ec2 100644
--- a/moonscript/compile/value.moon
+++ b/moonscript/compile/value.moon
@@ -52,25 +52,6 @@ value_compile =
     with @block "(function()", "end)()"
       \stm node, default_return
 
-  -- todo: convert to transformation
-  comprehension: (node) =>
-    _, exp, iter = unpack node
-
-    with @block!
-      tmp_name = \init_free_var "accum", {"table"}
-      len_name = \init_free_var "len", 0
-
-      action = (value) ->
-        table_append tmp_name, len_name, value
-
-      \stm node, action
-      \stm {"return", tmp_name}
-
-      .header, .footer = if .has_varargs
-        "(function(...)", "end)(...)"
-      else
-        "(function()", "end)()"
-
   chain: (node) =>
     callee = node[2]
 
diff --git a/moonscript/transform.lua b/moonscript/transform.lua
index 65d73b6..22ad247 100644
--- a/moonscript/transform.lua
+++ b/moonscript/transform.lua
@@ -2,6 +2,7 @@ module("moonscript.transform", package.seeall)
 local types = require("moonscript.types")
 local util = require("moonscript.util")
 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
 NameProxy = (function()
@@ -136,11 +137,22 @@ apply_to_last = function(stms, fn)
     return _accum_0
   end)()
 end
+local is_singular
+is_singular = function(body)
+  if #body ~= 1 then
+    return false
+  end
+  if "group" == ntype(body) then
+    return is_singular(body[2])
+  else
+    return true
+  end
+end
 local constructor_name = "new"
 local Transformer
 Transformer = function(transformers)
   local seen_nodes = { }
-  return function(n)
+  return function(n, ...)
     if seen_nodes[n] then
       return n
     end
@@ -149,7 +161,7 @@ Transformer = function(transformers)
       local transformer = transformers[ntype(n)]
       local res
       if transformer then
-        res = transformer(n) or n
+        res = transformer(n, ...) or n
       else
         res = n
       end
@@ -161,6 +173,42 @@ Transformer = function(transformers)
   end
 end
 stm = Transformer({
+  comprehension = function(node, action)
+    local _, exp, clauses = unpack(node)
+    action = action or function(exp)
+      return {
+        exp
+      }
+    end
+    local current_stms = action(exp)
+    for _, clause in reversed(clauses) do
+      local t = clause[1]
+      if t == "for" then
+        local names, iter
+        _, names, iter = unpack(clause)
+        current_stms = {
+          "foreach",
+          names,
+          iter,
+          current_stms
+        }
+      elseif t == "when" then
+        local cond
+        _, cond = unpack(clause)
+        current_stms = {
+          "if",
+          cond,
+          current_stms
+        }
+      else
+        current_stms = error("Unknown comprehension clause: " .. t)
+      end
+      current_stms = {
+        current_stms
+      }
+    end
+    return current_stms[1]
+  end,
   foreach = function(node)
     smart_node(node)
     if ntype(node.iter) == "unpack" then
@@ -437,45 +485,108 @@ stm = Transformer({
     return value
   end
 })
-local create_accumulator
-create_accumulator = function(body_index)
-  return function(node)
-    local accum_name = NameProxy("accum")
-    local value_name = NameProxy("value")
-    local len_name = NameProxy("len")
-    local body = apply_to_last(node[body_index], function(n)
-      return build.assign_one(value_name, n)
-    end)
-    table.insert(body, build["if"]({
-      cond = {
-        "exp",
-        value_name,
-        "!=",
-        "nil"
-      },
-      ["then"] = {
+local Accumulator
+Accumulator = (function()
+  local _parent_0 = nil
+  local _base_0 = {
+    body_idx = {
+      ["for"] = 4,
+      ["while"] = 3,
+      foreach = 4
+    },
+    convert = function(self, node)
+      local index = self.body_idx[ntype(node)]
+      node[index] = self:mutate_body(node[index])
+      return self:wrap(node)
+    end,
+    wrap = function(self, node)
+      return build.block_exp({
+        build.assign_one(self.accum_name, build.table()),
+        build.assign_one(self.len_name, 0),
+        node,
+        self.accum_name
+      })
+    end,
+    mutate_body = function(self, body, skip_nil)
+      if skip_nil == nil then
+        skip_nil = true
+      end
+      local val
+      if not skip_nil and is_singular(body) then
+        do
+          local _with_0 = body[1]
+          body = { }
+          val = _with_0
+        end
+      else
+        body = apply_to_last(body, function(n)
+          return build.assign_one(self.value_name, n)
+        end)
+        val = self.value_name
+      end
+      local update = {
         {
           "update",
-          len_name,
+          self.len_name,
           "+=",
           1
         },
-        build.assign_one(accum_name:index(len_name), value_name)
+        build.assign_one(self.accum_name:index(self.len_name), val)
       }
-    }))
-    node[body_index] = body
-    return build.block_exp({
-      build.assign_one(accum_name, build.table()),
-      build.assign_one(len_name, 0),
-      node,
-      accum_name
-    })
+      if skip_nil then
+        table.insert(body, build["if"]({
+          cond = {
+            "exp",
+            self.value_name,
+            "!=",
+            "nil"
+          },
+          ["then"] = update
+        }))
+      else
+        table.insert(body, build.group(update))
+      end
+      return body
+    end
+  }
+  _base_0.__index = _base_0
+  if _parent_0 then
+    setmetatable(_base_0, getmetatable(_parent_0).__index)
   end
+  local _class_0 = setmetatable({
+    __init = function(self)
+      self.accum_name = NameProxy("accum")
+      self.value_name = NameProxy("value")
+      self.len_name = NameProxy("len")
+    end
+  }, {
+    __index = _base_0,
+    __call = function(cls, ...)
+      local _self_0 = setmetatable({}, _base_0)
+      cls.__init(_self_0, ...)
+      return _self_0
+    end
+  })
+  _base_0.__class = _class_0
+  return _class_0
+end)()
+local default_accumulator
+default_accumulator = function(node)
+  return Accumulator():convert(node)
 end
 value = Transformer({
-  ["for"] = create_accumulator(4),
-  ["while"] = create_accumulator(3),
-  foreach = create_accumulator(4),
+  ["for"] = default_accumulator,
+  ["while"] = default_accumulator,
+  foreach = default_accumulator,
+  comprehension = function(node)
+    local a = Accumulator()
+    node = stm(node, function(exp)
+      return a:mutate_body({
+        exp
+      }, false)
+    end)
+    return a:wrap(node)
+  end,
   chain = function(node)
     local stub = node[#node]
     if type(stub) == "table" and stub[1] == "colon_stub" then
diff --git a/moonscript/transform.moon b/moonscript/transform.moon
index 767c06e..90cc834 100644
--- a/moonscript/transform.moon
+++ b/moonscript/transform.moon
@@ -5,6 +5,7 @@ types = require "moonscript.types"
 util = require "moonscript.util"
 data = require "moonscript.data"
 
+import reversed from util
 import ntype, build, smart_node, is_slice from types
 import insert from table
 
@@ -51,6 +52,7 @@ class Run
     self.fn state
 
 -- transform the last stm is a list of stms
+-- will puke on group
 apply_to_last = (stms, fn using nil) ->
   -- find last (real) exp
   last_exp_id = 0
@@ -66,23 +68,52 @@ apply_to_last = (stms, fn using nil) ->
     else
       stm
 
+-- is a body a sindle expression/statement
+is_singular = (body) ->
+  return false if #body != 1
+  if "group" == ntype body
+    is_singular body[2]
+  else
+    true
+
 constructor_name = "new"
 
 Transformer = (transformers) ->
+  -- this is bad, instance it for compiler
   seen_nodes = {}
-  (n) ->
+  (n, ...) ->
     return n if seen_nodes[n]
     seen_nodes[n] = true
     while true
       transformer = transformers[ntype n]
       res = if transformer
-        transformer(n) or n
+        transformer(n, ...) or n
       else
         n
       return n if res == n
       n = res
 
 stm = Transformer {
+  comprehension: (node, action) ->
+    _, exp, clauses = unpack node
+
+    action = action or (exp) -> {exp}
+
+    current_stms = action exp
+    for _, clause in reversed clauses
+      t = clause[1]
+      current_stms = if t == "for"
+        _, names, iter = unpack clause
+        {"foreach", names, iter, current_stms}
+      elseif t == "when"
+        _, cond = unpack clause
+        {"if", cond, current_stms}
+      else
+        error "Unknown comprehension clause: "..t
+      current_stms = {current_stms}
+
+    current_stms[1]
+
   foreach: (node) ->
     smart_node node
     if ntype(node.iter) == "unpack"
@@ -233,36 +264,68 @@ stm = Transformer {
     value
 }
 
-create_accumulator = (body_index) ->
-  (node) ->
-    accum_name = NameProxy "accum"
-    value_name = NameProxy "value"
-    len_name = NameProxy "len"
+class Accumulator
+  body_idx: { for: 4, while: 3, foreach: 4 }
 
-    body = apply_to_last node[body_index], (n) ->
-      build.assign_one value_name, n
+  new: =>
+    @accum_name = NameProxy "accum"
+    @value_name = NameProxy "value"
+    @len_name = NameProxy "len"
 
-    table.insert body, build["if"] {
-      cond: {"exp", value_name, "!=", "nil"}
-      then: {
-        {"update", len_name, "+=", 1}
-        build.assign_one accum_name\index(len_name), value_name
-      }
-    }
-
-    node[body_index] = body
+  -- wraps node and mutates body
+  convert: (node) =>
+    index = @body_idx[ntype node]
+    node[index] = @mutate_body node[index]
+    @wrap node
 
+  -- wrap the node into a block_exp
+  wrap: (node) =>
     build.block_exp {
-      build.assign_one accum_name, build.table!
-      build.assign_one len_name, 0
+      build.assign_one @accum_name, build.table!
+      build.assign_one @len_name, 0
       node
-      accum_name
+      @accum_name
     }
 
+  -- mutates the body of a loop construct to save last value into accumulator
+  -- can optionally skip nil results
+  mutate_body: (body, skip_nil=true) =>
+    val = if not skip_nil and is_singular body
+      with body[1]
+        body = {}
+    else
+      body = apply_to_last body, (n) ->
+        build.assign_one @value_name, n
+      @value_name
+
+    update = {
+      {"update", @len_name, "+=", 1}
+      build.assign_one @accum_name\index(@len_name), val
+    }
+
+    if skip_nil
+      table.insert body, build["if"] {
+        cond: {"exp", @value_name, "!=", "nil"}
+        then: update
+      }
+    else
+      table.insert body, build.group update
+
+    body
+
+default_accumulator = (node) ->
+  Accumulator!\convert node
+
 value = Transformer {
-  for: create_accumulator 4
-  while: create_accumulator 3
-  foreach: create_accumulator 4
+  for: default_accumulator
+  while: default_accumulator
+  foreach: default_accumulator
+
+  comprehension: (node) ->
+    a = Accumulator!
+    node = stm node, (exp) ->
+      a\mutate_body {exp}, false
+    a\wrap node
 
   -- pull out colon chain
   chain: (node) ->