Conditionals

if statements have the usual syntax (if <test> x else y) with implicit nestings (else if). The <test> expression is evaluated and the instruction x is evaluated if the value is different from false, nil or {}. Otherwise, the instruction y is evaluated, or the default value false is returned if no else part was provided.

if (x = 1) x := f(x,y)  else if (x > 1) x := g(x,y)  else (x := 3, f(x,y))  if (let y := 3 in x + y > 4 / x) print(x)

If statements must be inside a block, which means that if they are not inside a sequence surrounded by parenthesis they must be themselves surrounded by parenthesis (thus forming a block).

case is a set-based switch instruction: CLAIRE tests the branching sets one after another, executes the instruction associated with the first set that contains the object and exits the case instruction without any further testing. Hence, the default branch is associated with the set any. As for an if, the returned value is nil if no branch of the case is relevant :

case x ({1} x + 1, {2,3} x + 2, any x + 3)  case x (integer (x := 3, print(x)),          any error("~I is no good\n",x))

Note that the compiler will not accept a modification of the variable that is not consistent with the branch of the case (such as case x ({1} x := 2)). The expression on which the switching is performed is usually a variable, but can be any expression. However, it should not produce any side effect since it will be evaluated many times.

Starting with CLAIRE 3.3, only boolean expressions should be used in the <test> expression of a conditional statement. The implicit coercion of any expression into a Boolean is still supported, but should not be used any longer. The compiler will issue a warning if a non-boolean expression is used in an If.