Lua:

The built-in error system is absolutely horrendous You can implement a try-catch system by modifying the Lua interpreter; but it has no compatibility with the errors that are thrown by the built in functions. The fact they have __newindex instead of __setindex as the setter ... and __newindex is only fired when the key doesn't already exist. If it does, no metamethod is called at all. No good type comparison system. There's the type() function but it only handles the basic types (all tables are tables). It really needs to have a metamethod for type comparisons. I've implemented this before with an 'is' operator and a __type metamethod and it works really nicely. It's a bitch to define new keywords. You can do it, but the code inside Lua isn't well documented so it's kind of trial and error to find out how to get the result you want. This is a major issue when you want to implement the things I mentioned above yourself (not so much __setindex though, that's an easy modification). I can't use it in a web browser. Yeah not really a problem with the language itself, but damn, would I love to be able to use Lua instead of Javascript... :)

Python 3

both tabs & spaces allowed for indentation And you'd think people learn from the past (Makefile). Just pick spaces and forbid tabs. YAML got it right. lack of popular third-party libraries The standard library is great, but a lot of what makes Python 2 so powerful lies in the third-party realm. Python 2 got this right :-). IEEE floats Floating points in programming languages are confusing because they're different from the way we use them in math. Instead, the number operations should be viewed as expressions that are only converted to a decimal point format when needed (i.e. printing to a screen). Maple and Mathematica did this right I think. the character set for identifiers is too restricted list.empty? is better than list.is_empty or even len(list) != 0. Similarly, process.kill! would be better than process.kill. Ruby and lisp got this right. when calling a function you must always write parentheses It would be nice if we could omit them in unambiguous cases. How is it again? dict.items or dict.items()? Ruby got this one right, too.

EL -表达式语言，${…}和#{…JSF 2.0 Facelets用于从底层Java代码中提取数据。

All the fun things, like method calls with parameters and annotation based naming is only present in the EL in Java EE 6 which is only available in Glassfish v3. It is a royal pain to 1) get the right jars for an earlier Servlet 2.5 container, and 2) getting them to work without interfering with any previous implementation available in the container. Having only an earlier version of JSF like 1.2, takes away the method calls and leave you to work with f:setPropertyActionListener - http://weblogs.java.net/blog/2009/07/22/say-sayonara-spal - which, trust me on this, is not very nice. The EL parser has no idea of where the snippet it is to parse and interpret came from, so you tend to give everything an id so you at least can identify which tag made it grumpy. Eclipse gives a warning at every EL method call as it is JSF 1.2. only too.

BrainF * ck

你的亮点是图灵完备?!我可以在Perl正则表达式中做更多的事情! 缺少对象。来吧,人!就像，你好… 没有网络库。我只想刮一个网页，天哪。 没有一级函数。恭喜你——你可以同情你的Java朋友了。 一个无限的磁带存储，没有其他。这是如此的矫情，我们可能还在写Lisp。

Python:

No standard GUI toolkit (the community goes round and round about this but never seems to settle on anything). The evolution of tools and methods to distribute and install Python apps and libraries has been, well, rocky. (Although lately this seems to be moving closer to getting fixed.) CPython is still slow as interpreters go (although PyPy is looking pretty good these days, if it becomes the "standard" Python this problem goes away). You can't subclass built-in classes (e.g., list and dict) without overriding a lot of methods, even if all you want to do is a simple hook into an event (e.g., to hook into an item being added to or removed from the list, you need to override delitem, append, extend, insert, pop, and remove--there's no subclassable "change" event notification, nor any "protected" methods that factor out common code used by all the above methods). Up until virtualenv was invented, keeping separate Python environments for different purposes on one machine was a real pain.

Lua:

The built-in error system is absolutely horrendous You can implement a try-catch system by modifying the Lua interpreter; but it has no compatibility with the errors that are thrown by the built in functions. The fact they have __newindex instead of __setindex as the setter ... and __newindex is only fired when the key doesn't already exist. If it does, no metamethod is called at all. No good type comparison system. There's the type() function but it only handles the basic types (all tables are tables). It really needs to have a metamethod for type comparisons. I've implemented this before with an 'is' operator and a __type metamethod and it works really nicely. It's a bitch to define new keywords. You can do it, but the code inside Lua isn't well documented so it's kind of trial and error to find out how to get the result you want. This is a major issue when you want to implement the things I mentioned above yourself (not so much __setindex though, that's an easy modification). I can't use it in a web browser. Yeah not really a problem with the language itself, but damn, would I love to be able to use Lua instead of Javascript... :)