assert

#assert

##Syntax assert trueFalseExpn

##Description An assert statement is used to make sure that a certain requirement is met. This requirement is given by the trueFalseExpn. The trueFalseExpn is evaluated. If it is true, all is well and execution continues. If it is false, execution is terminated with an appropriate message.

##Example Make sure that n is positive.

    assert n > 0

##Example This program assumes that the textFile exists and can be opened, in other words, that the open will set the fileNumber to a positive stream number. If this is not true, the programmer wants the program halted immediately.

    var fileNumber : int
    open : fileNumber, "textFile", read
    assert fileNumber > 0

##Details In some Turing systems, checking can be turned off. If checking is turned off, assert statements may be ignored and as a result never cause termination.