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Learn Red ? Fundamentals of Red
book

Learn Red ? Fundamentals of Red

by Ivo Balbaert
May 2018
Beginner content levelBeginner
252 pages
6h 19m
English
Packt Publishing
Content preview from Learn Red ? Fundamentals of Red

Using error?

Use the type-test error? function in combination with try to test whether the code returns an error:

error? try [4 < "abc"] ;== true

The error? try phrase returns true in the case of an error and false otherwise.

Don't forget that try is followed by the code block that must be tested. If you use error? without it, the dangerous code is not executed, so no error! is generated, returning error? [4 < "abc"] ;== false.

We could use this to see if there is a runtime error with a condition test, phrased as if error?try:

if error? try [4 < "abc"][    print "Wrong input, enter an integer!"    quit ; or: continue]

We could also use either error? try:

either error? try [4 < "abc"][    print "Wrong input, enter an integer!"    quit ; or: continue
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Publisher Resources

ISBN: 9781789130706Supplemental Content