An exercise to get you started with lex

We'll be in Hobbs 113.

1. Log in to the Unix system using MobaXTerm.
2. You'll want a command (terminal) window, and an emacs editor window
3. In the private directory, create a subdirectory 322; in that, create a subdirectory yacc.
4. Using the editor emacs, put in this lex file and see if it works.  It's from http://ds9a.nl/lex-yacc/cvs/lex-yacc-howto.html, which you'll have read.

   /* 
      Lex file to recognize integer literals and words
      Will Briggs
      CS 322
      Spring 2018
   */
   
   %{
   #include <stdio.h>
   %}
   
   %%
   [0123456789]+           printf("INT_LITERAL\n");
   [a-zA-Z][a-zA-Z0-9]*    printf("WORD\n");
   %%

   All you need to know about C I/O is here.

• Save it as lex.l .
• Compile with these commands:
  flex lex.l
  ls
  gcc -o ex1 lex.yy.c -ll  #-ll means "include the lex library"; needed here, but not when using yacc
  ./ex1
• To run it, type
  ./ex1
  Enter whatever input you want, and hit Ctrl-D to end.  Or if input.txt is valid input, type
  ./ex1 < input.txt

5. Now, for grins, add the ability to your lex file to skip whitespace; and to recognize (),+-.  Hint:  if a character means something in lex (like + or ( ), put \ in front of it.

If you want to never have to type ./ for a command again:
cd ~
emacs .profile &
add this line to the end: $PATH = "$PATH:." and save.

To make editing easier, Escape, X, makefile-mode. There doesn't seem to be a lex mode, but makefile-mode is close enough. Modes tailor the editor to the type of program you're writing, especially in regard to tabbing.