Language Guide

CHAPTER 8
Handlers
222 Using Subroutines
Here’s a subroutine, called minimumValue, that returns the smaller of
two values:
--minimumValue subroutine:
on minimumValue(x, y)
if x  y then
return x
else
return y
end if
end minimumValue
--how to call minimumValue:
minimumValue(5, 105)
The first line of the minimumValue subroutine specifies the parameters of the
subroutine. These can be positional parameters—like x and y in the example—
where the order of the parameters is significant, or labeled parameters—
like those for AppleScript and application commands—where the order of
parameters other than the direct parameter doesn’t matter.
The minimumValue subroutine includes two Return statements. A Return
statement is one of the ways a subroutine can return a result. When
AppleScript executes a Return statement, it returns the value (if any) listed
in the statement and immediately exits the subroutine. If AppleScript executes
a Return statement without a value, it exits the subroutine immediately
and does not return a value.
If a subroutine does not include any Return statement, AppleScript executes
the statements in the subroutine and, after handling the last statement, returns
the value of the last statement in the subroutine. If the last statement does not
return a value, then the subroutine does not return a value.
When AppleScript has finished executing a subroutine, it passes control to the
place in the script immediately after the place where the subroutine was called.
If a subroutine call is part of an expression, AppleScript uses the value returned
by the subroutine to evaluate the expression. For example, to evaluate the
following expression, AppleScript calls the subroutine for minimumValue.
minimumValue(5, 105) + 100
After the value of minimumValue is returned, AppleScript evaluates the rest of
the expression.