[Ur] Pb with urblog and new release

[Adam Chlipala]

Manu wrote:
> trying to compile gian's urblog (a bit of a personal obsession I must 
> admit)
> I get this formidable trace :
>
> editor.ur:94:28-98:60: Expression is not a constructor function
> Expression:
> foldRX2[[(Type * Type)]] [fst[[Type]][[Type]]] [colMeta] [tr]

If you don't understand what the code is doing, then I don't recommend 
trying to compile it.  Further changes breaking backward compatibility 
are likely, and I don't want to be responsible for tracking all of the 
code that already exists out there.

In this case, I think you want to put an @ before foldRX2 (with no space 
between) and remove the constructor application that occurs at the 
location the error message references.

Also, if this code is really copied from an official demo, please just 
copy the latest version of that demo, rather than asking here.