Flow control

A good macro language needs of course flow control. The statements that take care of the flow control are:

while/endwhile

The word `while' should be followed by a blank and then an expression that is formed according to the above rules for expressions. As long as this expression evaluates into true the statements between the `while' and its matching `endwhile' statement will be executed, otherwise execution continues after the matching `endwhile' statement.

if

The if should be followed by one or more blank spaces and then an expression. The rules for this expression are identical to the rules for the expression in the while statement. If the expression has the logical value true the statements after the if are executed. If the expression has the value false execution continues either after a matching else or after a matching endif.

else

This statement is used together with an if and an endif statement. When execution reaches an else statement (without having been sent there directly from an if statement) the statements between the else and the matching endif are skipped. When execution reaches the else because of a `false' expression in an if statement the statements between the else and the endif will be executed.

endif

Needed to terminate a range of statements that come with an if statement. The occurrence of an if statement without a matching endif statement is a fatal error: the execution of the macro will be stopped. An endif statement that is superfluous is ignored.

goto

This should be followed by the name of a label. Control is passed to the statement after the label. If the label is not found execution of the macro will be halted and an error message will be given.

label

This should be followed by a name which is then interpreted as the name of the label.

return `returncode'

This statement causes the termination of the current macro. This doesn't generate an error condition as abnormal termination of a macro would do (like when running into a syntax error). On the other hand whatever comes after the word `return' is seen as a return code. It may be a complete expression as in the right hand side of a `set' command. The result of this expression is put in a dedicated variable that goes by the name returncode. If no return statement is used the returncode will be set to an empty string when the macro is finished. The variable returncode can be used to send information to the parent process. See also p. .