March 20

Symbol Tables and Symbol Table Update Actions

Objectives

• to have you demonstrate your parsers.
• to prepare you for the inclusion of semantic actions in your parse table for the construction of a symbol table.

Preparation

Special Notes

To Do - Program Test

You will need to follow your TA's instructions on how to swap programs for testing.  Use the test files you developed for your program to test the other group's program.  On your lab sheet, give the group number and a description of whether the executable actually executed, and what you observed in your testing of it.

To Do - The Symbol Table

1. Examine the following program (this is not exactly in micro Pascal form):

program lab1;
  var
    apple, candy: integer;
    y: float;
    zebra, xyz: integer;
    -- Point 1

  procedure mixit(a, b: integer; var x: float);
    var pony, apple, y: integer;
  begin --mixit
    pony := a + b
    -- Point 2
  end; --mixit

begin --lab1
  -- Point 3
  write(zebra);
end. --lab1

1a. Give a picture of the symbol table structure at points 1, 2, and 3 (see the comments in the program).  Use the single symbol table per scope approach.

1b. Repeat exercise 1a, but use the single symbol table approach as shown in lecture last Friday.  Use a hash table with 11 elements (0-10).  Assume that your hash function makes the following assignments.

apple 4, candy 7, y 0, zebra 7, xyz 10 mixit 8, a 3, b 1, x 9, pony 7.

2.   Repeat exercise 1a for the following program.

program lab1;
  var
    apple, candy: integer;
    y: float;
    zebra, xyz: integer;

  procedure mixit(a, b: integer; var x: float);
    var pony: integer;

    function fred(var q: float) returns integer;
    begin --fred
      -- Point 1
      fred := q + 1;
    end; -- fred

    function mary(x: integer) returns integer;
    begin --mary
      -- Point 2
      mary := x - 1;
    end; -- mary
  -- Point 3
    
  begin --mixit
    pony := a + b
  end; --mixit

begin --lab1
  -- Point 4
  write(zebra);
end. --lab1

3. Bring up the grammar for mPascal found on the class resources page.

• On the context free grammar page, print the sections that refer to variable, parameter, function, and procedure declarations.
• For each of the relevant grammar rules, mark the positions in the rules where enough information would be known from the parse to that point to insert the name of the identifier (variable names, parameter names, procedure name, or function name) and their attributes into the symbol table.   Call the action #insert for now.
• For each type of identifier (variable name, parameter name, procedure name, and function name) list the attributes that the name should have associated with it (according to the definition of mPascal).

To Turn In