Control Functions

break

Break out of a looping construct -- see the doWhile, for, while statements for further details.

Arguments: none

Return type: the empty List () is returned.

continue

Continue around a looping construct -- see the doWhile, for, while statements for further details.

Arguments: none

Return type: the empty List () is returned.

do

Perform a sequence of commands. For example:

    (do
        
        (print "Hello")
        (messageBox "Ooops")
        (print "there!")
    )

Return type: the result of evaluating the final expression is returned

doWhile

Perform a sequence of commands while the supplied condition evaluates to anything other than the empty List. Note that the condition is evaluated after the expressions have been evaluated.

This loop may be finished by the break statement, or the continue statement which interrupts the loop and goes round again without evaluating the remaining expressions.

For example:

    (doWhile (> n 0)
        
        (print n)
        (set n (- n 1))
    )

Return type: the result of evaluating the final expression is returned

for

Looping construct to work down a List or along an enumerator. For example:

    (for x (list 1 2 3)

        (print x)

        (set x (* x x))

        (print x)
    )

This loop may be finished by the break statement, or the continue statement which interrupts the loop and goes round again without evaluating the remaining expressions.

Arguments:

Return type: the result of evaluating the final expression is returned

if

The simple conditional test. The empty List () is taken to mean false. Any other item is taken to mean true in conditional tests.

For example:

    (if (> x 100)

        # here, we only have print if x is large!
        (print "large")

    )

    (if (> x 0)

        # print the word 'positive' is x is +ve
        (print "positive")

        # otherwise, x is -ve or zero
        (print "negative or zero")
    )

Return type: the empty List () is returned.

cond

The function cond provides a more powerful conditional test than the if function. It takes 1 or more List clauses where each clause typically consists of a test followed by a sequence of expressions to evaluate if the test succeeds. The clauses are worked on in order. When the first test expression evaluates to true then the following expressions within the clause are evaluated -- the result of the final evaluation being returned.

If a clause contains just a test with no subsequent expressions, the value of the clause is the value of the evaluation of the test.

cond is most often used to produce a multiple if statement e.g.

    (cond ( test1  expr1 )
          ( test2  expr2 )
          ...
          ( testN  exprN )
    )

Return type: an object of any type may be returned

return

Return a value from a script function. Whenever a return expression is evaluated, the script function is terminated and the supplied value returned.

Arguments:

Return type: any type can be returned

set

Assign a variable to hold the reference to the argument object.

    (set x 234)

Arguments:

Return type: the empty List () is returned.

A second, more powerful, form of the function can assign a list of variables to elements of a list e.g.

    (set (x y z) (list 2 3 4))

If the length of the values-list is greater than the length of the variables-list, then any remaining values in the values-list remain un-assigned.

unset

Remove any assignment for the supplied variable.

Arguments:

Return type: the empty List () is returned.

setShared

Put the supplied data into the shared region so that it can be easily shared across threads within the same process.

    (setShared "x" 234)

Arguments:

Return type: the empty List () is returned.

getShared

Get the supplied data from the shared region -- see setShared.

    (getShared "x")

Arguments:

Return type: the Object which was previously put into the shared region using setShared.

while

Loop while a given condition holds. Note that the condition is evaluated and tested before the expressions are evaluated. For example:

    (while (> x 0)

        (print x)

        (set x (- x 1))
    )

This loop may be finished by the break statement, or the continue statement which interrupts the loop and goes round again without evaluating the remaining expressions.

Arguments:

Return type: the empty List () is returned.