The CAR holds the data for one element of the list, and the CDR holds the CONS that makes up the head of the rest of the list. This leads some programmers to assume that destructive functions always modify the argument to match the result. Dangers of destructive changes When you use destructive functions you should be sure to only modify data that your program has constructed at runtime. This function is effectively modifying itself, as it changes the constant data which is bound to the variable L . This book may not be reproduced without the written consent of its author.
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