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Selection Statements

The general types of selection statements in Limbo are: if, case, and alt.

Note: See Channels in Chapter 3 for information about alt.

if

The if statement selects statements to execute based on the evaluation of an expression. The two general formats of the if statement are:

	if (expression) statement
	if (expression) statement else statment

The expression must produce an int result. If the result is true (non-zero), then the first statement (or block) is executed. Otherwise, the statement (or block) following the else is executed, if the else clause is present.

For example:

	if (guess == randnum)
		sys->print("Correct!\n");
	else
		sys->print("Oh, sorry.\n");

if statements can be nested. In Limbo, an else statement always refers to the nearest if statement that is within the same block as the else and that is not already associated with an else. For example:

	if (i == j) {
		if (k == l) {		...		}
		if (m == n) {
			...
		} else {					# this else is associated with
			...				# 'if (m == n)'
		}
	} else	 {					# this else is associated with 
		...					# `if (i ==j)'
	}

case

The case statement selects from multiple statements to execute based on the evaluation of an expression. The general form of the case statement is:

	case expression {
		qualifier =>
			statement
		...
	}

The expression must produce an int or a string result. The qualifier(s) can be simple constants, multiple constants, and ranges. They must evaluate uniquely, none of the ranges or constants may overlap. If there is no matching qualifier and a default qualifer, *, is present, then the default is selected.

Each qualifer and the statements that follow up to the next qualifier form a block. Each block breaks by default; no explicit break statement is needed.

There is no "drop through" nature in the Limbo case. A qualifier is not required to have statements, but execution does not continue through the next qualifier's statements.

The general syntax of a Limbo case statement is similar to that of the C/C++ switch statement. For example:

	case direction {
	"north" or "east" =>
		...
	"south" =>
		...
	* =>
		...

case statements can be nested. For example:

	case x {
	1 =>
		case y {
			0 =>
				...
			1 =>
				...
		}
	2 =>
		...

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