diff --git a/nomsu.lua b/nomsu.lua
index e24cdb5..bb38efd 100644
--- a/nomsu.lua
+++ b/nomsu.lua
@@ -205,7 +205,7 @@ do
       elseif type(signature) == 'table' and type(signature[1]) == 'string' then
         signature = self:get_stubs(signature)
       end
-      assert(type(thunk) == 'function', "Bad thunk: " .. tostring(repr(thunk)))
+      self:assert(type(thunk) == 'function', "Bad thunk: " .. tostring(repr(thunk)))
       local canonical_args = nil
       local canonical_escaped_args = nil
       local aliases = { }
@@ -223,7 +223,7 @@ do
         local _des_0 = signature[_index_0]
         local stub, arg_names, escaped_args
         stub, arg_names, escaped_args = _des_0[1], _des_0[2], _des_0[3]
-        assert(stub, "NO STUB FOUND: " .. tostring(repr(signature)))
+        self:assert(stub, "NO STUB FOUND: " .. tostring(repr(signature)))
         if self.debug then
           self:writeln(tostring(colored.bright("DEFINING RULE:")) .. " " .. tostring(colored.underscore(colored.magenta(repr(stub)))) .. " " .. tostring(colored.bright("WITH ARGS")) .. " " .. tostring(colored.dim(repr(arg_names))))
         end
@@ -235,12 +235,12 @@ do
           end
         end
         if canonical_args then
-          assert(equivalent(set(arg_names), canonical_args), "Mismatched args")
+          self:assert(equivalent(set(arg_names), canonical_args), "Mismatched args")
         else
           canonical_args = set(arg_names)
         end
         if canonical_escaped_args then
-          assert(equivalent(escaped_args, canonical_escaped_args), "Mismatched escaped args")
+          self:assert(equivalent(escaped_args, canonical_escaped_args), "Mismatched escaped args")
         else
           canonical_escaped_args = escaped_args
           def.escaped_args = escaped_args
@@ -496,7 +496,7 @@ do
       end
       str = str:gsub("\r", "")
       local tree = parse(str, filename)
-      assert(tree, "In file " .. tostring(colored.blue(filename)) .. " failed to parse:\n" .. tostring(colored.onyellow(colored.black(str))))
+      self:assert(tree, "In file " .. tostring(colored.blue(filename)) .. " failed to parse:\n" .. tostring(colored.onyellow(colored.black(str))))
       if self.debug then
         self:writeln("PARSE TREE:")
         self:print_tree(tree, "    ")
@@ -525,8 +525,8 @@ do
         debug.sethook(timeout, "", max_operations)
       end
       local tree = self:parse(src, filename)
-      assert(tree, "Tree failed to compile: " .. tostring(src))
-      assert(tree.type == "File", "Attempt to run non-file: " .. tostring(tree.type))
+      self:assert(tree, "Tree failed to compile: " .. tostring(src))
+      self:assert(tree.type == "File", "Attempt to run non-file: " .. tostring(tree.type))
       local buffer = { }
       local return_value = nil
       local _list_0 = tree.value
@@ -611,7 +611,7 @@ end);]]):format(concat(buffer, "\n"))
       if force_inline == nil then
         force_inline = false
       end
-      assert(tree, "No tree provided.")
+      self:assert(tree, "No tree provided.")
       if not tree.type then
         self:errorln(debug.traceback())
         self:error("Invalid tree: " .. tostring(repr(tree)))
@@ -801,7 +801,7 @@ end);]]):format(concat(buffer, "\n"))
       end
     end,
     tree_to_lua = function(self, tree, filename)
-      assert(tree, "No tree provided.")
+      self:assert(tree, "No tree provided.")
       if not tree.type then
         self:errorln(debug.traceback())
         self:error("Invalid tree: " .. tostring(repr(tree)))
@@ -1199,6 +1199,14 @@ end)]]):format(concat(lua_bits, "\n"))
         end
       end))
     end,
+    assert = function(self, condition, msg)
+      if msg == nil then
+        msg = ''
+      end
+      if not condition then
+        return self:error(msg)
+      end
+    end,
     error = function(self, msg)
       local error_msg = colored.red("ERROR!")
       if msg then
diff --git a/nomsu.moon b/nomsu.moon
index 896cd4b..13ff129 100755
--- a/nomsu.moon
+++ b/nomsu.moon
@@ -169,7 +169,7 @@ class NomsuCompiler
             signature = @get_stubs {signature}
         elseif type(signature) == 'table' and type(signature[1]) == 'string'
             signature = @get_stubs signature
-        assert type(thunk) == 'function', "Bad thunk: #{repr thunk}"
+        @assert type(thunk) == 'function', "Bad thunk: #{repr thunk}"
         canonical_args = nil
         canonical_escaped_args = nil
         aliases = {}
@@ -177,15 +177,15 @@ class NomsuCompiler
         def = {:thunk, :src, :is_macro, aliases:{}, def_number:@@def_number, defs:@defs}
         where_defs_go = (getmetatable(@defs) or {}).__newindex or @defs
         for {stub, arg_names, escaped_args} in *signature
-            assert stub, "NO STUB FOUND: #{repr signature}"
+            @assert stub, "NO STUB FOUND: #{repr signature}"
             if @debug then @writeln "#{colored.bright "DEFINING RULE:"} #{colored.underscore colored.magenta repr(stub)} #{colored.bright "WITH ARGS"} #{colored.dim repr(arg_names)}"
             for i=1,#arg_names-1 do for j=i+1,#arg_names
                 if arg_names[i] == arg_names[j] then @error "Duplicate argument in function #{stub}: '#{arg_names[i]}'"
             if canonical_args
-                assert equivalent(set(arg_names), canonical_args), "Mismatched args"
+                @assert equivalent(set(arg_names), canonical_args), "Mismatched args"
             else canonical_args = set(arg_names)
             if canonical_escaped_args
-                assert equivalent(escaped_args, canonical_escaped_args), "Mismatched escaped args"
+                @assert equivalent(escaped_args, canonical_escaped_args), "Mismatched escaped args"
             else
                 canonical_escaped_args = escaped_args
                 def.escaped_args = escaped_args
@@ -324,7 +324,7 @@ class NomsuCompiler
             @writeln("#{colored.bright "PARSING:"}\n#{colored.yellow str}")
         str = str\gsub("\r","")
         tree = parse(str, filename)
-        assert tree, "In file #{colored.blue filename} failed to parse:\n#{colored.onyellow colored.black str}"
+        @assert tree, "In file #{colored.blue filename} failed to parse:\n#{colored.onyellow colored.black str}"
         if @debug
             @writeln "PARSE TREE:"
             @print_tree tree, "    "
@@ -338,8 +338,8 @@ class NomsuCompiler
                 @error "Execution quota exceeded. Your code took too long."
             debug.sethook timeout, "", max_operations
         tree = @parse(src, filename)
-        assert tree, "Tree failed to compile: #{src}"
-        assert tree.type == "File", "Attempt to run non-file: #{tree.type}"
+        @assert tree, "Tree failed to compile: #{src}"
+        @assert tree.type == "File", "Attempt to run non-file: #{tree.type}"
 
         buffer = {}
         return_value = nil
@@ -405,7 +405,7 @@ end);]])\format(concat(buffer, "\n"))
 
     tree_to_nomsu: (tree, force_inline=false)=>
         -- Return <nomsu code>, <is safe for inline use>
-        assert tree, "No tree provided."
+        @assert tree, "No tree provided."
         if not tree.type
             @errorln debug.traceback()
             @error "Invalid tree: #{repr(tree)}"
@@ -535,7 +535,7 @@ end);]])\format(concat(buffer, "\n"))
 
     tree_to_lua: (tree, filename)=>
         -- Return <lua code for value>, <additional lua code>
-        assert tree, "No tree provided."
+        @assert tree, "No tree provided."
         if not tree.type
             @errorln debug.traceback()
             @error "Invalid tree: #{repr(tree)}"
@@ -786,6 +786,10 @@ end)]])\format(concat(lua_bits, "\n"))
             var = var.value
         (var\gsub "%W", (verboten)->
             if verboten == "_" then "__" else ("_%x")\format(verboten\byte!))
+    
+    assert: (condition, msg='')=>
+        if not condition
+            @error(msg)
 
     error: (msg)=>
         error_msg = colored.red "ERROR!"