diff --git a/lib/collections.nom b/lib/collections.nom
index 3d87924..fb66468 100644
--- a/lib/collections.nom
+++ b/lib/collections.nom
@@ -48,7 +48,7 @@ compile [length of %list, size of %list, size %list, number of %list, len %list]
 compile [%list ->* %indices] to:
     assert ((%indices's "type") == "List") ".."
         Expected List for chained lookup, not \(%indices's "type")
-    %ret = "\(%list as lua)"
+    set %ret = "\(%list as lua)"
     for %index in (%indices's "value"):
         %ret join= "[\(%index as lua)]"
     return "\%ret"
@@ -72,33 +72,23 @@ compile [remove index %index from %list] to:
 
 
 action [flatten %lists]:
-    %flat = []
+    set %flat = []
     for %list in %lists:
         for %item in %list:
             add %item to %flat
     return %flat
 
 action [dict %items]:
-    %dict = []
-    for %pair in %items:
-        %dict -> (%pair -> 1) = (%pair -> 2)
-    return %dict
+    {(%->1)=(%->2) for all %items}
 
 action [entries in %dict]:
-    %entries = []
-    for %k = %v in %dict:
-        add {key=%k, value=%v} to %entries
-    return %entries
+    [{key=%k, value=%v} for %k=%v in %dict]
 
 action [keys in %dict]:
-    %keys = []
-    for %k = %v in %dict: add %k to %keys
-    return %keys
+    [%k for %k=%v in %dict]
 
 action [values in %dict]:
-    %values = []
-    for %k = %v in %dict: add %v to %values
-    return %values
+    [%v for %k=%v in %dict]
 
 # List Comprehension
 compile [%expression for %item in %iterable] to:
diff --git a/lib/control_flow.nom b/lib/control_flow.nom
index 5adcbd5..d06de4f 100644
--- a/lib/control_flow.nom
+++ b/lib/control_flow.nom
@@ -55,9 +55,9 @@ immediately:
     compile [do next repeat-loop] to code: "goto continue_repeat;"
     compile [stop repeat-loop] to code: "goto stop_repeat;"
     compile [repeat while %condition %body] to code:
-        %continue_labels = (..)
+        set %continue_labels = (..)
             "\n::continue_repeat::;" if (tree %body has function call \(do next repeat-loop)) else ""
-        %code = ".."
+        set %code = ".."
             while \(%condition as lua) do
             \(%body as lua statements)\
             ..\%continue_labels
@@ -92,19 +92,19 @@ immediately:
         for %var from %start to %stop via %step %body
     ..to code:
         lua> "local \%continue_labels, \%code, \%stop_labels"
-        %continue_labels = ""
+        set %continue_labels = ""
         if (tree %body has function call \(do next for-loop)):
             %continue_labels join= "\n::continue_for::;"
         if (tree %body has function call (tree \(do next %) with {""=%var})):
             %continue_labels join= "\n::continue_\(nomsu "var_to_lua_identifier" [%var])::;"
         # This trashes the loop variables, just like in Python.
-        %code = ".."
+        set %code = ".."
             for i=\(%start as lua),\(%stop as lua),\(%step as lua) do
             \(%var as lua) = i;
             \(%body as lua statements)\
             ..\%continue_labels
             end --numeric for-loop
-        %stop_labels = ""
+        set %stop_labels = ""
         if (tree %body has function call \(stop for-loop)):
             %stop_labels join= "\n::stop_for::;"
         if (tree %body has function call (tree \(stop %) with {""=%var})):
@@ -128,25 +128,25 @@ immediately:
 immediately:
     compile [for %var in %iterable %body] to code:
         lua> "local \%continue_labels, \%stop_labels, \%code, \%stop_labels"
-        %continue_labels = ""
+        set %continue_labels = ""
         if (tree %body has function call \(do next for-loop)):
             %continue_labels join= "\n::continue_for::;"
         if (tree %body has function call (tree \(do next %) with {""=%var})):
             %continue_labels join= "\n::continue_\(nomsu "var_to_lua_identifier" [%var])::;"
         # This trashes the loop variables, just like in Python.
-        %code = ".."
+        set %code = ".."
             for i,value in ipairs(\(%iterable as lua)) do
             \(%var as lua) = value;
             \(%body as lua statements)\
             ..\%continue_labels
             end --foreach-loop
-        %stop_labels = ""
+        set %stop_labels = ""
         if (tree %body has function call \(stop for-loop)):
             %stop_labels join= "\n::stop_for::;"
         if (tree %body has function call (tree \(stop %) with {""=%var})):
             %stop_labels join= "\n::stop_\(nomsu "var_to_lua_identifier" [%var])::;"
         if %stop_labels != "":
-            %code = ".."
+            set %code = ".."
                 do --for-loop label scope
                 \%code\%stop_labels
                 end --for-loop label scope
@@ -156,7 +156,7 @@ immediately:
 # Dict iteration (lua's "pairs()")
 immediately:
     compile [for %key = %value in %iterable %body] to code:
-        %continue_labels = ""
+        set %continue_labels = ""
         if (tree %body has function call \(do next for-loop)):
             %continue_labels join= "\n::continue_for::;"
         if (tree %body has function call (tree \(do next %x) with {x=%key})):
@@ -164,13 +164,13 @@ immediately:
         if (tree %body has function call (tree \(do next %) with {""=%value})):
             %continue_labels join= "\n::continue_\(nomsu "var_to_lua_identifier" [%value])::;"
         # This trashes the loop variables, just like in Python.
-        %code = ".."
+        set %code = ".."
             for key,value in ipairs(\(%iterable as lua)) do
             \(%key as lua), \(%value as lua) = key, value;
             \(%body as lua statements)\
             ..\%continue_labels
             end --foreach-loop
-        %stop_labels = ""
+        set %stop_labels = ""
         if (tree %body has function call \(stop for-loop)):
             %stop_labels join= "\n::stop_for::;"
         if (tree %body has function call (tree \(stop %) with {""=%key})):
@@ -189,23 +189,23 @@ immediately:
 immediately:
     compile [when %body] to code:
         lua> "local \%result, \%fallthroughs, \%first"
-        %result = ""
-        %fallthroughs = []
-        %first = (yes)
+        set %result = ""
+        set %fallthroughs = []
+        set %first = (yes)
         for %func_call in (%body's "value"):
             lua> "local \%tokens, \%star, \%condition, \%action"
             assert ((%func_call's "type") == "FunctionCall") ".."
                 Invalid format for 'when' statement. Only '*' blocks are allowed.
-            %tokens = (%func_call's "value")
-            %star = (%tokens -> 1)
+            set %tokens = (%func_call's "value")
+            set %star = (%tokens -> 1)
             assert (=lua "\%star and \%star.type == 'Word' and \%star.value == '*'") ".."
                 Invalid format for 'when' statement. Lines must begin with '*'
 
-            %condition = (%tokens -> 2)
+            set %condition = (%tokens -> 2)
             assert %condition ".."
                 Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"
 
-            %action = (%tokens -> 3)
+            set %action = (%tokens -> 3)
             if (%action == (nil)):
                 lua do> "table.insert(\%fallthroughs, \%condition)"
                 do next %func_call
@@ -217,7 +217,7 @@ immediately:
                     \(%action as lua statements)
                 stop for-loop
             ..else:
-                %condition = (%condition as lua)
+                set %condition = (%condition as lua)
                 for all %fallthroughs:
                     %condition join= " or \(% as lua)"
                 %result join= ".."
@@ -225,8 +225,8 @@ immediately:
                     \("if" if %first else "elseif") \%condition then
                     \(%action as lua statements)
 
-            %fallthroughs = []
-            %first = (no)
+            set %fallthroughs = []
+            set %first = (no)
 
         if (%result != ""):
             %result join= "\nend"
@@ -235,22 +235,22 @@ immediately:
 # Switch statement
 immediately:
     compile [when %branch_value == ? %body] to code:
-        %result = ""
-        %fallthroughs = []
-        %first = (yes)
+        set %result = ""
+        set %fallthroughs = []
+        set %first = (yes)
         for %func_call in (%body's "value"):
             assert ((%func_call's "type") == "FunctionCall") ".."
                 Invalid format for 'when' statement. Only '*' blocks are allowed.
-            %tokens = (%func_call's "value")
-            %star = (%tokens -> 1)
+            set %tokens = (%func_call's "value")
+            set %star = (%tokens -> 1)
             assert (=lua "\%star and \%star.type == 'Word' and \%star.value == '*'") ".."
                 Invalid format for 'when' statement. Lines must begin with '*'
 
-            %condition = (%tokens -> 2)
+            set %condition = (%tokens -> 2)
             assert %condition ".."
                 Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"
 
-            %action = (%tokens -> 3)
+            set %action = (%tokens -> 3)
             if (%action == (nil)):
                 lua> "table.insert(\%fallthroughs, \%condition)"
                 do next %func_call
@@ -262,7 +262,7 @@ immediately:
                     \(%action as lua statements)
                 stop for-loop
             ..else:
-                %condition = "branch_value == (\(%condition as lua))"
+                set %condition = "branch_value == (\(%condition as lua))"
                 for all %fallthroughs:
                     %condition join= " or (branch_value == \(% as lua))"
                 %result join= ".."
@@ -270,11 +270,11 @@ immediately:
                     \("if" if %first else "elseif") \%condition then
                     \(%action as lua statements)
 
-            %fallthroughs = []
-            %first = (no)
+            set %fallthroughs = []
+            set %first = (no)
 
         if (%result != ""):
-            %result = ".."
+            set %result = ".."
                 do --when == ?
                 local branch_value = \(%branch_value as lua);\
                 ..\%result
diff --git a/lib/operators.nom b/lib/operators.nom
index 95441ea..f576e40 100644
--- a/lib/operators.nom
+++ b/lib/operators.nom
@@ -57,7 +57,7 @@ compile [%str |%start|] to: "\(%str as lua):sub(\(%start as lua), \(%start as lu
 compile [%str |%start - %stop|] to: "\(%str as lua):sub(\(%start as lua), \(%stop as lua))"
 
 # Variable assignment operator, and += type versions
-compile [%var = %val] to code:
+compile [set %var = %val] to code:
     lua> ".."
         if \%var.type == 'List' and \%val.type == 'List' then
             local lhs = {};
@@ -92,11 +92,26 @@ compile [%x > %y] to: "(\(%x as lua) > \(%y as lua))"
 compile [%x <= %y] to: "(\(%x as lua) <= \(%y as lua))"
 compile [%x >= %y] to: "(\(%x as lua) >= \(%y as lua))"
 # == and != do equivalence checking, rather than identity checking
-compile [%a == %b] to: "nomsu.utils.equivalent(\(%a as lua), \(%b as lua))"
-compile [%a != %b] to: "(not nomsu.utils.equivalent(\(%a as lua), \(%b as lua)))"
-# For strict identity checking:
-compile [%x === %y] to: "(\(%x as lua) == \(%y as lua))"
-compile [%x !== %y] to: "(\(%x as lua) ~= \(%y as lua))"
+compile [%a is %b, %a = %b, %a == %b] to:
+    lua> ".."
+        local safe = {Text=true, Number=true};
+        local a_lua, b_lua = nomsu:tree_to_lua(\%a).expr, nomsu:tree_to_lua(\%b).expr;
+        if safe[\%a.type] or safe[\%b.type] then
+            return "("..a_lua.." == "..b_lua..")";
+        else
+            return "nomsu.utils.equivalent("..a_lua..", "..b_lua..")";
+        end
+compile [%a isn't %b, %a is not %b, %a != %b] to:
+    lua> ".."
+        local safe = {Text=true, Number=true};
+        local a_lua, b_lua = nomsu:tree_to_lua(\%a).expr, nomsu:tree_to_lua(\%b).expr;
+        if safe[\%a.type] or safe[\%b.type] then
+            return "("..a_lua.." ~= "..b_lua..")";
+        else
+            return "(not nomsu.utils.equivalent("..a_lua..", "..b_lua.."))";
+        end
+# For strict identity checking, use (%x's id) is (%y's id)
+compile [%'s id, id of %] to: "nomsu.ids[\(% as lua)]"
 
 # 3-part chained comparisons
 # (uses a lambda to avoid re-evaluating middle value, while still being an expression)
diff --git a/lib/utils2.nom b/lib/utils2.nom
index b0b9dd9..c8fa3b4 100644
--- a/lib/utils2.nom
+++ b/lib/utils2.nom
@@ -15,16 +15,16 @@ compile [do %action] to code:
 
 # With statement
 compile [with %assignments %action] to code:
-    %data = []
+    set %data = []
     for %i = %assignment in (%assignments' "value"):
-        %tokens = (%assignment's "value")
-        %var = (%tokens -> 1)
-        %eq = (%tokens -> 2)
+        set %tokens = (%assignment's "value")
+        set %var = (%tokens -> 1)
+        set %eq = (%tokens -> 2)
         assert (=lua "\%eq and \%eq.type == 'Word' and \%eq.value == '='") ".."
             Invalid format for 'with' statement. List entries must have the form %var = (value)
-        %value = (%tokens -> 3)
+        set %value = (%tokens -> 3)
         add {i=%i, var=%var, value=%value} to %data
-    %setup = (..)
+    set %setup = (..)
         join (..)
             "local old_value\(%->"i") = \((%->"var") as lua); \((%->"var") as lua) = \((%->"value") as lua);"
             ..for all %data
diff --git a/nomsu.lua b/nomsu.lua
index 31bbe28..478ca8b 100644
--- a/nomsu.lua
+++ b/nomsu.lua
@@ -1,6 +1,7 @@
 local re = require('re')
 local lpeg = require('lpeg')
 local utils = require('utils')
+local new_uuid = require('uuid')
 local repr, stringify, min, max, equivalent, set, is_list, sum
 repr, stringify, min, max, equivalent, set, is_list, sum = utils.repr, utils.stringify, utils.min, utils.max, utils.equivalent, utils.set, utils.is_list, utils.sum
 local colors = setmetatable({ }, {
@@ -427,7 +428,7 @@ do
       local tree = self:parse(src, filename)
       self:assert(tree, "Failed to parse: " .. tostring(src))
       self:assert(tree.type == "File", "Attempt to run non-file: " .. tostring(tree.type))
-      local lua = self:tree_to_lua(tree, filename)
+      local lua = self:tree_to_lua(tree)
       local lua_code = lua.statements or (lua.expr .. ";")
       lua_code = "-- File: " .. tostring(filename) .. "\n" .. lua_code
       local ret = self:run_lua(lua_code)
@@ -492,7 +493,7 @@ end]]):format(lua_code))
       return ret
     end,
     tree_to_value = function(self, tree, filename)
-      local code = "return (function(nomsu)\nreturn " .. tostring(self:tree_to_lua(tree, filename).expr) .. ";\nend);"
+      local code = "return (function(nomsu)\nreturn " .. tostring(self:tree_to_lua(tree).expr) .. ";\nend);"
       code = "-- Tree to value: " .. tostring(filename) .. "\n" .. code
       if self.debug then
         self:writeln(tostring(colored.bright("RUNNING LUA TO GET VALUE:")) .. "\n" .. tostring(colored.blue(colored.bright(code))))
@@ -695,7 +696,7 @@ end]]):format(lua_code))
         return error("Unsupported value_to_nomsu type: " .. tostring(type(value)))
       end
     end,
-    tree_to_lua = function(self, tree, filename)
+    tree_to_lua = function(self, tree)
       self:assert(tree, "No tree provided.")
       if not tree.type then
         self:error("Invalid tree: " .. tostring(repr(tree)))
@@ -703,13 +704,13 @@ end]]):format(lua_code))
       local _exp_0 = tree.type
       if "File" == _exp_0 then
         if #tree.value == 1 then
-          return self:tree_to_lua(tree.value[1], filename)
+          return self:tree_to_lua(tree.value[1])
         end
         local lua_bits = { }
         local _list_0 = tree.value
         for _index_0 = 1, #_list_0 do
           local line = _list_0[_index_0]
-          local lua = self:tree_to_lua(line, filename)
+          local lua = self:tree_to_lua(line)
           if not lua then
             self:error("No lua produced by " .. tostring(repr(line)))
           end
@@ -732,7 +733,7 @@ end]]):format(lua_code))
         local _list_0 = tree.value
         for _index_0 = 1, #_list_0 do
           local arg = _list_0[_index_0]
-          local lua = self:tree_to_lua(arg, filename)
+          local lua = self:tree_to_lua(arg)
           if #tree.value == 1 and lua.expr and not lua.statements then
             return {
               expr = lua.expr
@@ -781,7 +782,7 @@ end]]):format(lua_code))
             if tok.type == "Word" then
               insert(bits, tok.value)
             else
-              local lua = self:tree_to_lua(tok, filename)
+              local lua = self:tree_to_lua(tok)
               self:assert(lua.statements == nil, "non-expression value inside math expression")
               insert(bits, lua.expr)
             end
@@ -802,7 +803,7 @@ end]]):format(lua_code))
               _continue_0 = true
               break
             end
-            local lua = self:tree_to_lua(tok, filename)
+            local lua = self:tree_to_lua(tok)
             self:assert(lua.expr, "Cannot use " .. tostring(tok.src) .. " as an argument, since it's not an expression.")
             insert(args, lua.expr)
             _continue_0 = true
@@ -848,7 +849,7 @@ end]]):format(lua_code))
               insert(concat_parts, repr(string_buffer))
               string_buffer = ""
             end
-            local lua = self:tree_to_lua(bit, filename)
+            local lua = self:tree_to_lua(bit)
             if self.debug then
               self:writeln((colored.bright("INTERP:")))
               self:print_tree(bit)
@@ -885,7 +886,7 @@ end]]):format(lua_code))
         local _list_0 = tree.value
         for _index_0 = 1, #_list_0 do
           local item = _list_0[_index_0]
-          local lua = self:tree_to_lua(item, filename)
+          local lua = self:tree_to_lua(item)
           if lua.statements then
             self:error("Cannot use [[" .. tostring(item.src) .. "]] as a list item, since it's not an expression.")
           end
@@ -905,12 +906,12 @@ end]]):format(lua_code))
               expr = repr(entry.dict_key.value)
             }
           else
-            key_lua = self:tree_to_lua(entry.dict_key, filename)
+            key_lua = self:tree_to_lua(entry.dict_key)
           end
           if key_lua.statements then
             self:error("Cannot use [[" .. tostring(entry.dict_key.src) .. "]] as a dict key, since it's not an expression.")
           end
-          local value_lua = self:tree_to_lua(entry.dict_value, filename)
+          local value_lua = self:tree_to_lua(entry.dict_value)
           if value_lua.statements then
             self:error("Cannot use [[" .. tostring(entry.dict_value.src) .. "]] as a dict value, since it's not an expression.")
           end
@@ -1163,7 +1164,7 @@ end]]):format(lua_code))
           if type(bit) == "string" then
             insert(concat_parts, bit)
           else
-            local lua = self:tree_to_lua(bit, filename)
+            local lua = self:tree_to_lua(bit)
             if lua.statements then
               self:error("Cannot use [[" .. tostring(bit.src) .. "]] as a string interpolation value, since it's not an expression.")
             end
@@ -1241,6 +1242,14 @@ end]]):format(lua_code))
         ["#vars"] = { },
         ["#loaded_files"] = { }
       }
+      self.ids = setmetatable({ }, {
+        __mode = "k",
+        __index = function(self, key)
+          local id = new_uuid()
+          self[key] = id
+          return id
+        end
+      })
       if parent then
         setmetatable(self.defs, {
           __index = parent.defs
@@ -1252,7 +1261,6 @@ end]]):format(lua_code))
           __index = parent["#loaded_files"]
         })
       end
-      self.callstack = { }
       self.compilestack = { }
       self.debug = false
       self.utils = utils
diff --git a/nomsu.moon b/nomsu.moon
index 63ccee0..78c72ce 100755
--- a/nomsu.moon
+++ b/nomsu.moon
@@ -13,6 +13,7 @@
 re = require 're'
 lpeg = require 'lpeg'
 utils = require 'utils'
+new_uuid = require 'uuid'
 {:repr, :stringify, :min, :max, :equivalent, :set, :is_list, :sum} = utils
 colors = setmetatable({}, {__index:->""})
 colored = setmetatable({}, {__index:(_,color)-> ((msg)-> colors[color]..(msg or '')..colors.reset)})
@@ -147,11 +148,17 @@ class NomsuCompiler
         @write_err = (...)=> io.stderr\write(...)
         -- Use # to prevent someone from defining a function that has a namespace collision.
         @defs = {["#vars"]:{}, ["#loaded_files"]:{}}
+        @ids = setmetatable({}, {
+            __mode: "k"
+            __index: (key)=>
+                id = new_uuid!
+                @[key] = id
+                return id
+        })
         if parent
             setmetatable(@defs, {__index:parent.defs})
             setmetatable(@defs["#vars"], {__index:parent["#vars"]})
             setmetatable(@defs["#loaded_files"], {__index:parent["#loaded_files"]})
-        @callstack = {}
         @compilestack = {}
         @debug = false
         @utils = utils
@@ -281,7 +288,7 @@ class NomsuCompiler
         @assert tree, "Failed to parse: #{src}"
         @assert tree.type == "File", "Attempt to run non-file: #{tree.type}"
 
-        lua = @tree_to_lua(tree, filename)
+        lua = @tree_to_lua(tree)
         lua_code = lua.statements or (lua.expr..";")
         lua_code = "-- File: #{filename}\n"..lua_code
         ret = @run_lua(lua_code)
@@ -335,7 +342,7 @@ end]]\format(lua_code))
         return ret
     
     tree_to_value: (tree, filename)=>
-        code = "return (function(nomsu)\nreturn #{@tree_to_lua(tree, filename).expr};\nend);"
+        code = "return (function(nomsu)\nreturn #{@tree_to_lua(tree).expr};\nend);"
         code = "-- Tree to value: #{filename}\n"..code
         if @debug
             @writeln "#{colored.bright "RUNNING LUA TO GET VALUE:"}\n#{colored.blue colored.bright(code)}"
@@ -476,7 +483,7 @@ end]]\format(lua_code))
                 error("Unsupported value_to_nomsu type: #{type(value)}")
 
     @math_patt: re.compile [[ "%" (" " [*/^+-] " %")+ ]]
-    tree_to_lua: (tree, filename)=>
+    tree_to_lua: (tree)=>
         -- Return <lua code for value>, <additional lua code>
         @assert tree, "No tree provided."
         if not tree.type
@@ -485,10 +492,10 @@ end]]\format(lua_code))
         switch tree.type
             when "File"
                 if #tree.value == 1
-                    return @tree_to_lua(tree.value[1], filename)
+                    return @tree_to_lua(tree.value[1])
                 lua_bits = {}
                 for line in *tree.value
-                    lua = @tree_to_lua line, filename
+                    lua = @tree_to_lua line
                     if not lua
                         @error "No lua produced by #{repr line}"
                     if lua.statements then insert lua_bits, lua.statements
@@ -501,7 +508,7 @@ end]]\format(lua_code))
             when "Block"
                 lua_bits = {}
                 for arg in *tree.value
-                    lua = @tree_to_lua arg, filename
+                    lua = @tree_to_lua arg
                     if #tree.value == 1 and lua.expr and not lua.statements
                         return expr:lua.expr
                     if lua.statements then insert lua_bits, lua.statements
@@ -529,7 +536,7 @@ end]]\format(lua_code))
                         if tok.type == "Word"
                             insert bits, tok.value
                         else
-                            lua = @tree_to_lua(tok, filename)
+                            lua = @tree_to_lua(tok)
                             @assert(lua.statements == nil, "non-expression value inside math expression")
                             insert bits, lua.expr
                     remove @compilestack
@@ -539,7 +546,7 @@ end]]\format(lua_code))
                 args = {}
                 for tok in *tree.value
                     if tok.type == "Word" then continue
-                    lua = @tree_to_lua(tok, filename)
+                    lua = @tree_to_lua(tok)
                     @assert(lua.expr, "Cannot use #{tok.src} as an argument, since it's not an expression.")
                     insert args, lua.expr
 
@@ -561,7 +568,7 @@ end]]\format(lua_code))
                     if string_buffer ~= ""
                         insert concat_parts, repr(string_buffer)
                         string_buffer = ""
-                    lua = @tree_to_lua bit, filename
+                    lua = @tree_to_lua bit
                     if @debug
                         @writeln (colored.bright "INTERP:")
                         @print_tree bit
@@ -582,7 +589,7 @@ end]]\format(lua_code))
             when "List"
                 items = {}
                 for item in *tree.value
-                    lua = @tree_to_lua item, filename
+                    lua = @tree_to_lua item
                     if lua.statements
                         @error "Cannot use [[#{item.src}]] as a list item, since it's not an expression."
                     insert items, lua.expr
@@ -594,10 +601,10 @@ end]]\format(lua_code))
                     key_lua = if entry.dict_key.type == "Word"
                         {expr:repr(entry.dict_key.value)}
                     else
-                        @tree_to_lua entry.dict_key, filename
+                        @tree_to_lua entry.dict_key
                     if key_lua.statements
                         @error "Cannot use [[#{entry.dict_key.src}]] as a dict key, since it's not an expression."
-                    value_lua = @tree_to_lua entry.dict_value, filename
+                    value_lua = @tree_to_lua entry.dict_value
                     if value_lua.statements
                         @error "Cannot use [[#{entry.dict_value.src}]] as a dict value, since it's not an expression."
                     key_str = key_lua.expr\match([=[["']([a-zA-Z_][a-zA-Z0-9_]*)['"]]=])
@@ -755,7 +762,7 @@ end]]\format(lua_code))
                 if type(bit) == "string"
                     insert concat_parts, bit
                 else
-                    lua = @tree_to_lua bit, filename
+                    lua = @tree_to_lua bit
                     if lua.statements
                         @error "Cannot use [[#{bit.src}]] as a string interpolation value, since it's not an expression."
                     insert concat_parts, lua.expr
diff --git a/uuid.lua b/uuid.lua
new file mode 100644
index 0000000..878727b
--- /dev/null
+++ b/uuid.lua
@@ -0,0 +1,23 @@
+-- A simple UUID function based on RFC 4122: http://www.ietf.org/rfc/rfc4122.txt
+local function uuid()
+    local r = math.random
+    -- Set all the other bits to randomly (or pseudo-randomly) chosen values.
+    local bytes = {
+        r(2^(4*8)), --time-low
+        r(2^(2*8)), --time-mid
+        r(2^(2*8-4)), --time-high-and-version
+        r(2^(1*8-2)), --clock-seq-and-reserved
+        r(2^(1*8)), --clock-seq-low
+        r(2^(3*8)), r(2^(3*8)), --node
+    } 
+    -- Set the four most significant bits (bits 12 through 15) of the
+    -- time_hi_and_version field to the 4-bit version number from
+    -- Section 4.1.3.
+    bytes[3] = bit32.bor(bytes[3], 0x4000)
+    -- Set the two most significant bits (bits 6 and 7) of the
+    -- clock_seq_hi_and_reserved to zero and one, respectively.
+    bytes[4] = bit32.bor(bytes[4], 0xC0)
+    return ("%08x-%04x-%04x-%02x%02x-%6x%6x"):format(unpack(bytes))
+end
+
+return uuid