[PRL] values and expressions

[Riccardo Pucella]

> Is it a really bad thing not to have the values of a language be a
> subset of the expressions?

As Richard said, depends on the context, and what you want to do. 

For instance, if you are mainly interested in giving a semantics or
studying the properties of a semantics, you can often get away with giving
the semantics for the full language - which includes all the values as
expressions - and then restrict the source language in which the programmer
can write programs to be a subset of all the expressions in the language.
Your semantics is then simpler (you only have one, as opposed to two), but
it makes some theorems harder to prove. 


 Cheers, 
 Riccardo