added special treatment for nested function for clang

I changed the definition of the nested function "Welcome_Pair" to make it compile on my Macbook, which runs clang-500.2.79. This is the output of `clang --version` on my site:

```
Apple LLVM version 5.0 (clang-500.2.79) (based on LLVM 3.3svn)
Target: x86_64-apple-darwin13.0.2
Thread model: posix
```

I'm not sure if this change is correct since I'm new to this kind of block syntax, I hope it works.