s6.l and s6.y provide the skeleton of your project. There are a few things that are not implemented. You have to implement them and that will complete your project. There are three tables in this project - Symbol Table, string table and a Tree Table (tree is embedded in a table with 5 entries - operator and two operands and the tables where the operands are located). The convention I have used: 0 referes to Symbol Table, 1 refers to Tree Table and 2 refers to String Table. For example, the following statements

modcomp=2004;
grade=100;
print "My Grade is A as my score is=";
score = grade*modcomp;
print score;
print newline;

This is the tree. The first two entries in the tree implement modcomp=2004. The first tree entry evaluates by loading from the symbol table (0) entry 2. The second tree entry evaluates the first entry(0) of the tree table (1) and stores in the first entry (1) of the symbol table(0). You can follow the rest of the tree.

mytree (0 )     (L  0  2  0  0 )
mytree (1 )     (=  0  1  1  0 )
mytree (2 )     (L  0  4  0  0 )
mytree (3 )     (=  0  3  1  2 )
mytree (4 )     (;  1  1  1  3 )
mytree (5 )     (p  2  1  0  0 )
mytree (6 )     (;  1  4  1  5 )
mytree (7 )     (L  0  3  0  0 )
mytree (8 )     (L  0  1  0  0 )
mytree (9 )     (*  1  7  1  8 )
mytree (10 )    (=  0  5  1  9 )
mytree (11 )    (;  1  6  1 10 )
mytree (12 )    (L  0  5  0  0 )
mytree (13 )    (P  1 12  0  0 )
mytree (14 )    (;  1 11  1 13 )
mytree (15 )    (q  2  5  0  0 )
mytree (16 )    (;  1 14  1 15 )

Output
My Grade is A as my score is=200400

Symbol Table
 1: modcomp 2004
 2: 2004 2004
 3: grade 100
 4: 100 100
 5: score 200400

String table
My Grade is A as my score is=