assert test-expression (message string-expression)?


You can use assert to verify any assumptions you are making at any given point in your code. To test an assumption, insert the word assert at an appropriate point in your code and follow it with a test expression that tests your assumption. If the test condition returns true, your program continues. If the test expression returns false, OmniMark throws a run-time error. You can specify an error message to accompany the error by adding a message parameter:

  global integer number-of-guesses initial { 10 }
     assert number-of-guesses > 0 message "Illegal value for number-of-guesses"
     output "You have " || "d" % number-of-guesses || " guesses."

In this program the number of guesses is a global and therefore configurable on the command line. The assert statement tests to make sure that it is not set to a value that does not make sense.

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