Are declared variables a bad thing?

[Michael Kay]

> Once during my computer studies I was told (paraphrasing) 
> "Global variables are bad. Bad, bad, BAD!"
> 
> Why? It is bad style, making for buggy, opaque code and 
> harder program maintenance.

It's bad in procedural languages because updates to global variables are a
common source of bugs.

It does no harm in declarative languages, where global variables can't be
updated.

Michael Kay
http://www.saxonica.com/