diff --git a/error_handling.lua b/error_handling.lua
index 27022aa..8d6e7d9 100644
--- a/error_handling.lua
+++ b/error_handling.lua
@@ -1,5 +1,6 @@
 local debug_getinfo = debug.getinfo
 local Files = require("files")
+local pretty_error = require("pretty_errors")
 local RED = "\027[31m"
 local BRIGHT_RED = "\027[31;1m"
 local RESET = "\027[0m"
@@ -54,16 +55,7 @@ debug.getinfo = function(thread, f, what)
         end
         info.short_src = info.source:match('@([^[]*)') or info.short_src
         if info.name then
-          do
-            local tmp = info.name:match("^A_([a-zA-Z0-9_]*)$")
-            if tmp then
-              info.name = tmp:gsub("_", " "):gsub("x([0-9A-F][0-9A-F])", function(self)
-                return string.char(tonumber(self, 16))
-              end)
-            else
-              info.name = info.name
-            end
-          end
+          info.name = "action '" .. tostring(calling_fn.name:from_lua_id()) .. "'"
         else
           info.name = "main chunk"
         end
@@ -72,12 +64,78 @@ debug.getinfo = function(thread, f, what)
   end
   return info
 end
-local print_error
-print_error = function(error_message, start_fn, stop_fn)
-  io.stderr:write(tostring(RED) .. "ERROR: " .. tostring(BRIGHT_RED) .. tostring(error_message or "") .. tostring(RESET) .. "\n")
-  io.stderr:write("stack traceback:\n")
-  local level = 1
-  local found_start = false
+local enhance_error
+enhance_error = function(error_message, start_fn, stop_fn)
+  if not (error_message and error_message:match("\x1b")) then
+    error_message = error_message or ""
+    do
+      local fn = error_message:match("attempt to call a nil value %(global '(.*)'%)")
+      if fn then
+        if fn:match("x[0-9A-F][0-9A-F]") then
+          error_message = "The action '" .. tostring(fn:from_lua_id()) .. "' is not defined."
+        end
+      end
+    end
+    local level = 2
+    while true do
+      local calling_fn = debug_getinfo(level)
+      if not calling_fn then
+        break
+      end
+      level = level + 1
+      local filename, file, line_num
+      do
+        local map = SOURCE_MAP and SOURCE_MAP[calling_fn.source]
+        if map then
+          if calling_fn.currentline then
+            line_num = assert(map[calling_fn.currentline])
+          end
+          local start, stop
+          filename, start, stop = calling_fn.source:match('@([^[]*)%[([0-9]+):([0-9]+)]')
+          if not filename then
+            filename, start = calling_fn.source:match('@([^[]*)%[([0-9]+)]')
+          end
+          assert(filename)
+          file = Files.read(filename)
+        else
+          filename = calling_fn.short_src
+          file = Files.read(filename)
+          if calling_fn.short_src:match("%.moon$") and type(MOON_SOURCE_MAP[file]) == 'table' then
+            local char = MOON_SOURCE_MAP[file][calling_fn.currentline]
+            line_num = file:line_number_at(char)
+          else
+            line_num = calling_fn.currentline
+          end
+        end
+      end
+      if file and filename and line_num then
+        local start = 1
+        local lines = file:lines()
+        for i = 1, line_num - 1 do
+          start = start + #lines[i] + 1
+        end
+        local stop = start + #lines[line_num]
+        start = start + #lines[line_num]:match("^ *")
+        error_message = pretty_error({
+          title = "Error",
+          error = error_message,
+          source = file,
+          start = start,
+          stop = stop,
+          filename = filename
+        })
+        break
+      end
+      if calling_fn.func == xpcall then
+        break
+      end
+    end
+  end
+  local ret = {
+    tostring(RED) .. "ERROR: " .. tostring(BRIGHT_RED) .. tostring(error_message or "") .. tostring(RESET),
+    "stack traceback:"
+  }
+  local level = 2
   while true do
     local _continue_0 = false
     repeat
@@ -85,19 +143,15 @@ print_error = function(error_message, start_fn, stop_fn)
       if not calling_fn then
         break
       end
-      level = level + 1
-      if not (found_start) then
-        if calling_fn.func == start_fn then
-          found_start = true
-        end
-        _continue_0 = true
+      if calling_fn.func == xpcall then
         break
       end
+      level = level + 1
       local name = calling_fn.name and "function '" .. tostring(calling_fn.name) .. "'" or nil
       if calling_fn.linedefined == 0 then
         name = "main chunk"
       end
-      if name == "run_lua_fn" then
+      if name == "function 'run_lua_fn'" then
         _continue_0 = true
         break
       end
@@ -120,16 +174,7 @@ print_error = function(error_message, start_fn, stop_fn)
           end
           assert(filename)
           if calling_fn.name then
-            do
-              local tmp = calling_fn.name:match("^A_([a-zA-Z0-9_]*)$")
-              if tmp then
-                name = "action '" .. tostring(tmp:gsub("_", " "):gsub("x([0-9A-F][0-9A-F])", function(self)
-                  return string.char(tonumber(self, 16))
-                end)) .. "'"
-              else
-                name = "action '" .. tostring(calling_fn.name) .. "'"
-              end
-            end
+            name = "action '" .. tostring(calling_fn.name:from_lua_id()) .. "'"
           else
             name = "main chunk"
           end
@@ -192,10 +237,7 @@ print_error = function(error_message, start_fn, stop_fn)
           end
           if file and (calling_fn.short_src:match("%.moon$") or file:match("^#![^\n]*moon\n")) and type(MOON_SOURCE_MAP[file]) == 'table' then
             local char = MOON_SOURCE_MAP[file][calling_fn.currentline]
-            line_num = 1
-            for _ in file:sub(1, char):gmatch("\n") do
-              line_num = line_num + 1
-            end
+            line_num = file:line_number_at(char)
             line = tostring(CYAN) .. tostring(calling_fn.short_src) .. ":" .. tostring(line_num) .. " in " .. tostring(name or '?') .. tostring(RESET)
           else
             line_num = calling_fn.currentline
@@ -216,12 +258,9 @@ print_error = function(error_message, start_fn, stop_fn)
           end
         end
       end
-      io.stderr:write(line, "\n")
+      table.insert(ret, line)
       if calling_fn.istailcall then
-        io.stderr:write("      " .. tostring(DIM) .. "(...tail calls...)" .. tostring(RESET) .. "\n")
-      end
-      if calling_fn.func == stop_fn then
-        break
+        table.insert(ret, "      " .. tostring(DIM) .. "(...tail calls...)" .. tostring(RESET))
       end
       _continue_0 = true
     until true
@@ -229,19 +268,20 @@ print_error = function(error_message, start_fn, stop_fn)
       break
     end
   end
-  return io.stderr:flush()
+  return table.concat(ret, "\n")
 end
 local guard
 guard = function(fn)
-  local error_handler
-  error_handler = function(error_message)
-    print_error(error_message, error_handler, fn)
-    local EXIT_FAILURE = 1
-    return os.exit(EXIT_FAILURE)
+  local err
+  ok, err = xpcall(fn, enhance_error)
+  if not ok then
+    io.stderr:write(err)
+    io.stderr:flush()
+    return os.exit(1)
   end
-  return xpcall(fn, error_handler)
 end
 return {
   guard = guard,
+  enhance_error = enhance_error,
   print_error = print_error
 }
diff --git a/error_handling.moon b/error_handling.moon
index c22a3ae..3252727 100644
--- a/error_handling.moon
+++ b/error_handling.moon
@@ -1,6 +1,7 @@
 -- This file contains the logic for making nicer error messages
 debug_getinfo = debug.getinfo
 Files = require "files"
+pretty_error = require("pretty_errors")
 export SOURCE_MAP
 
 RED = "\027[31m"
@@ -31,7 +32,7 @@ debug.getinfo = (thread,f,what)->
     else debug_getinfo(thread,f,what)
     if not info or not info.func then return info
     if info.short_src or info.source or info.linedefine or info.currentline
-        -- TODO: get name properly
+        -- TODO: reduce duplicate code
         if map = SOURCE_MAP[info.source]
             if info.currentline
                 info.currentline = assert(map[info.currentline])
@@ -40,31 +41,71 @@ debug.getinfo = (thread,f,what)->
             if info.lastlinedefined
                 info.lastlinedefined = assert(map[info.lastlinedefined])
             info.short_src = info.source\match('@([^[]*)') or info.short_src
-            -- TODO: get name properly
             info.name = if info.name
-                if tmp = info.name\match("^A_([a-zA-Z0-9_]*)$")
-                    tmp\gsub("_"," ")\gsub("x([0-9A-F][0-9A-F])", => string.char(tonumber(@, 16)))
-                else info.name
+                "action '#{calling_fn.name\from_lua_id!}'"
             else "main chunk"
     return info
 
-print_error = (error_message, start_fn, stop_fn)->
-    io.stderr\write("#{RED}ERROR: #{BRIGHT_RED}#{error_message or ""}#{RESET}\n")
-    io.stderr\write("stack traceback:\n")
+enhance_error = (error_message, start_fn, stop_fn)->
+    unless error_message and error_message\match("\x1b")
+        error_message or= ""
+        if fn = error_message\match("attempt to call a nil value %(global '(.*)'%)")
+            if fn\match "x[0-9A-F][0-9A-F]"
+                error_message = "The action '#{fn\from_lua_id!}' is not defined."
+        level = 2
+        while true
+            -- TODO: reduce duplicate code
+            calling_fn = debug_getinfo(level)
+            if not calling_fn then break
+            level += 1
+            local filename, file, line_num
+            if map = SOURCE_MAP and SOURCE_MAP[calling_fn.source]
+                if calling_fn.currentline
+                    line_num = assert(map[calling_fn.currentline])
+                filename,start,stop = calling_fn.source\match('@([^[]*)%[([0-9]+):([0-9]+)]')
+                if not filename
+                    filename,start = calling_fn.source\match('@([^[]*)%[([0-9]+)]')
+                assert(filename)
+                file = Files.read(filename)
+            else
+                filename = calling_fn.short_src
+                file = Files.read(filename)
+                if calling_fn.short_src\match("%.moon$") and type(MOON_SOURCE_MAP[file]) == 'table'
+                    char = MOON_SOURCE_MAP[file][calling_fn.currentline]
+                    line_num = file\line_number_at(char)
+                else
+                    line_num = calling_fn.currentline
 
-    level = 1
-    found_start = false
+            if file and filename and line_num
+                start = 1
+                lines = file\lines!
+                for i=1,line_num-1 do start += #lines[i] + 1
+                stop = start + #lines[line_num]
+                start += #lines[line_num]\match("^ *")
+                error_message = pretty_error{
+                    title:"Error"
+                    error:error_message, source:file
+                    start:start, stop:stop, filename:filename
+                }
+                break
+            if calling_fn.func == xpcall then break
+
+
+    ret = {
+        "#{RED}ERROR: #{BRIGHT_RED}#{error_message or ""}#{RESET}"
+        "stack traceback:"
+    }
+
+    level = 2
     while true
         -- TODO: reduce duplicate code
         calling_fn = debug_getinfo(level)
         if not calling_fn then break
+        if calling_fn.func == xpcall then break
         level += 1
-        unless found_start
-            if calling_fn.func == start_fn then found_start = true
-            continue
         name = calling_fn.name and "function '#{calling_fn.name}'" or nil
         if calling_fn.linedefined == 0 then name = "main chunk"
-        if name == "run_lua_fn" then continue
+        if name == "function 'run_lua_fn'" then continue
         line = nil
         if map = SOURCE_MAP and SOURCE_MAP[calling_fn.source]
             if calling_fn.currentline
@@ -78,11 +119,8 @@ print_error = (error_message, start_fn, stop_fn)->
             if not filename
                 filename,start = calling_fn.source\match('@([^[]*)%[([0-9]+)]')
             assert(filename)
-            -- TODO: get name properly
             name = if calling_fn.name
-                if tmp = calling_fn.name\match("^A_([a-zA-Z0-9_]*)$")
-                    "action '#{tmp\gsub("_"," ")\gsub("x([0-9A-F][0-9A-F])", => string.char(tonumber(@, 16)))}'"
-                else "action '#{calling_fn.name}'"
+                "action '#{calling_fn.name\from_lua_id!}'"
             else "main chunk"
 
             file = Files.read(filename)
@@ -123,8 +161,7 @@ print_error = (error_message, start_fn, stop_fn)->
             
             if file and (calling_fn.short_src\match("%.moon$") or file\match("^#![^\n]*moon\n")) and type(MOON_SOURCE_MAP[file]) == 'table'
                 char = MOON_SOURCE_MAP[file][calling_fn.currentline]
-                line_num = 1
-                for _ in file\sub(1,char)\gmatch("\n") do line_num += 1
+                line_num = file\line_number_at(char)
                 line = "#{CYAN}#{calling_fn.short_src}:#{line_num} in #{name or '?'}#{RESET}"
             else
                 line_num = calling_fn.currentline
@@ -137,18 +174,17 @@ print_error = (error_message, start_fn, stop_fn)->
                 if err_line = lines[line_num]
                     offending_statement = "#{BRIGHT_RED}#{err_line\match("^[ ]*(.*)$")}#{RESET}"
                     line ..= "\n        "..offending_statement
-        io.stderr\write(line,"\n")
+        table.insert ret, line
         if calling_fn.istailcall
-            io.stderr\write("      #{DIM}(...tail calls...)#{RESET}\n")
-        if calling_fn.func == stop_fn then break
+            table.insert ret, "      #{DIM}(...tail calls...)#{RESET}"
 
-    io.stderr\flush!
+    return table.concat(ret, "\n")
 
 guard = (fn)->
-    error_handler = (error_message)->
-        print_error error_message, error_handler, fn
-        EXIT_FAILURE = 1
-        os.exit(EXIT_FAILURE)
-    xpcall(fn, error_handler)
+    ok, err = xpcall(fn, enhance_error)
+    if not ok
+        io.stderr\write err
+        io.stderr\flush!
+        os.exit 1
 
-return {:guard, :print_error}
+return {:guard, :enhance_error, :print_error}
diff --git a/lib/core/errors.nom b/lib/core/errors.nom
index 8027228..a84b580 100644
--- a/lib/core/errors.nom
+++ b/lib/core/errors.nom
@@ -25,7 +25,7 @@ use "core/control_flow"
         local _a, _b = \($a as lua expr), \($b as lua expr)
         if _a ~= _b then
             at_1_fail(\(quote "\($a.source)"),
-                "Assumption failed: This value was "..tostring(_a).." when it was supposed to be "..tostring(_b)..".")
+                "Assumption failed: This value was "..tostring(_a).." but it was expected to be "..tostring(_b)..".")
         end
     end
 ")
@@ -35,7 +35,7 @@ use "core/control_flow"
         local _a, _b = \($a as lua expr), \($b as lua expr)
         if _a == _b then
             at_1_fail(\(quote "\($a.source)"),
-                "Assumption failed: This value was "..tostring(_a).." when it wasn't supposed to be.")
+                "Assumption failed: This value was "..tostring(_a).." but it wasn't expected to be.")
         end
     end
 ")
@@ -76,10 +76,10 @@ test:
         Lua ("
             do
                 local _fell_through = false
-                local _result = {pcall(function()
+                local _result = {xpcall(function()
                     \($action as lua)
                     _fell_through = true
-                end)}
+                end, enhance_error)}
                 if _result[1] then
                     \$success_lua
                 else
@@ -123,10 +123,10 @@ test:
 (do $action then always $final_action) compiles to ("
     do -- do/then always
         local _fell_through = false
-        local _results = {pcall(function()
+        local _results = {xpcall(function()
             \($action as lua)
             _fell_through = true
-        end)}
+        end, enhance_error)}
         \($final_action as lua)
         if not _results[1] then error(_results[2], 0) end
         if not _fell_through then return table.unpack(_results, 2) end
diff --git a/nomsu_environment.lua b/nomsu_environment.lua
index 204b151..d9014c3 100644
--- a/nomsu_environment.lua
+++ b/nomsu_environment.lua
@@ -10,6 +10,7 @@ do
 end
 local SyntaxTree = require("syntax_tree")
 local Files = require("files")
+local Errhand = require("error_handling")
 local make_parser = require("parser")
 local pretty_error = require("pretty_errors")
 local make_tree
@@ -137,6 +138,7 @@ nomsu_environment = Importer({
   NomsuCode_from = (function(src, ...)
     return NomsuCode:from(src, ...)
   end),
+  enhance_error = Errhand.enhance_error,
   SOURCE_MAP = { },
   getfenv = getfenv,
   _1_as_nomsu = tree_to_nomsu,
diff --git a/nomsu_environment.moon b/nomsu_environment.moon
index 522b4c9..f26a7e9 100644
--- a/nomsu_environment.moon
+++ b/nomsu_environment.moon
@@ -4,6 +4,7 @@
 {:List, :Dict, :Text} = require 'containers'
 SyntaxTree = require "syntax_tree"
 Files = require "files"
+Errhand = require "error_handling"
 make_parser = require("parser")
 pretty_error = require("pretty_errors")
 
@@ -61,6 +62,7 @@ nomsu_environment = Importer{
     :LuaCode, :NomsuCode, :Source
     LuaCode_from: ((src, ...)-> LuaCode\from(src, ...)),
     NomsuCode_from: ((src, ...)-> NomsuCode\from(src, ...)),
+    enhance_error: Errhand.enhance_error
     SOURCE_MAP: {},
     getfenv:getfenv,