Expressions Overview

Perfect has a wide range of expression types. In Perfect, expressions do not have side-effects, so expressions are never ambiguous.

Some types of expression have preconditions. So, what's a precondition?

For the moment, just think of preconditions as conditions that must be true for the expression to be legal.
For example, if total and number are integer variables, the expression total/number needs the precondition
number ~= 0 (i.e. "number not-equal-to zero").

In the rest of Basic Tutorial Two, we will look at operator expressions (including comparisons).

We will discuss how you can use brackets

• to force evaluation order
• to introduce names for temporary values
• and build conditional expressions.

and we will find out about calling functions and constructors.

More complicated stuff is left for Basic Tutorial 3. That is where we will cover

• expressions with bound variables, which are powerful constructs that usually involve collections
• type conversions and type enquiries.

Next:  Operator expressions