How to use fyacc
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Five directories are involved: dir1, dir2, dir3, dir4, dir5.
The inital content of them are:
  dir1:  The basic fyacc files.
  dir2:  An abbreviated yacc file (lang.ay).
  dir3:  A Makefile for the language (lang) and a usual lex file (lang.l).
  dir4:  A program (prog) in the language described by lang.ay and lang.l.
  dir5:  A java program (main.java) which operates on an abstract syntax tree.

1. Go to dir1.  Write 'make'.  This creates the executable 'fyacc'.
   
2. Go to dir2.  Copy fyacc from dir1.  Write 'fyacc < lang.ay > lang.y'.
   This creates both lang.y and classes.java.

3. Go to dir3.  Copy lang.y from dir2.  Write 'make'.  This creates
   the executable 'lang'.

4. Go to dir4.  Copy lang from dir3.  Write 'lang < prog'.  This produces 
   a Java file treeout.java.  To look at treeout.java, write 
   'less treeout.java'.

5. Go to dir5.  Copy class.java from dir2 and treeout.java from dir4.
   Compile all the java code and run.