If¶

Although it is pretty intuitive, it is worth having a short review of the syntax for if statements and if expressions. Let’s start with if expressions because they are the simplest to explain. An if expression has the form:

if cexpr then expr1 else expr2;

where cexpr is a conditional expression (that will evaluate to a Boolean value), expr1 is the value the expression will have if cexpr evaluates to true and expr2 is the value the expression will have if cexpr evaluates to false.

An if statement has the general syntax:

if cond1 then
  // Statements used if cond1==true
elseif cond2 then
  // Statements used if cond1==false and cond2==true
// ...
elseif condn then
  // Statements used if all previous conditions are false
  // and condn==true
else
  // Statements used otherwise
end if;

It is important to note that when an if statement appears in an equation section, the number of equations must be the same regardless of which branch through the if statement is taken (this applies in the presence of elseif as well). One exception is the use of if within an initial equation or initial algorithm section where an else clause is not required since the number of equations doesn’t have to be same for both branches. Another notable exception is the use of if within Functions where, again, there is not requirement that the number of equations be the same across both branches.

A special case here is when you have an if statement that looks like this:

if cond then
  x = y;
else
  x = z;
end if;

We can see that in both branches, a value is assigned to x. As such, an equivalent way to write this using an if expression would be:

x = if cond then y else z;

The advantage of the second formulation is that it may make it easier for a tool to optimize the code generation in the case of an if expression.