The "$TIGER/chap1" directory referred on Appel pp 10 is available as the /c/cs421/as/as1 directory on any ZOO machines. The file "as1.sml" contains the datatype definition similar to Program 1.5 on Appel pp. 9, though the actual names for the data constructors are different. Please write your program based on the datatypes defined in "as1.sml".
The files "test1a.sml" and "test1b.sml" are useful for testing your code.
Extra Credits: Exercises 1.1 described in Modern Compiler Implementation in ML, Chapter 1, on page 12 - 13.