When would you ever use an Expression?
The puppet language supports expressions.
I can't find a reason that you would ever need to use one. Here is their example in the documentation which appears to be useless.
5<9 ($operatingsystem != 'Solaris') $kernel in ['linux', 'solaris'] !str2bool($is_virtual)
And another example
(90 < 7) and ('Solaris' == 'Solaris') # resolves to false (90 < 7) or ('solaris' in ['linux', 'solaris']) # resolves to true
Why would you ever need to compare 2 numbers like this? Wouldn't it be better to use an if statement and variables?