Exploring Translation

Summary: In today's lab, you will explore the translation of Stupid, Sam's Totally Unintelligble Program Instruction Doohicky, to PAL, the pseduo-assembly language that I've written (okay, started to write) as an intermediate language for your compilers.

Contents:

• Background
• Exercises
  • Exercise 1: Stupid Basics
  • Exercise 2: Translating Boolean Expressions
  • Exercise 3: Adding Operations
  • Exercise 4: Adding Comparison Operations
  • Exercise 5: Adding Boolean Operations

Warning: Stupid, the Stupid translator, PAL, and this lab are under development. All of them probably have many bugs. Let me know which ones you notice.

Collaboration: Feel free to work on this lab in pairs or trios.

Turning It In: You do not need to turn in this lab. It is intended primarily for your edification.

Grading: Since you're not going to turn it in, I'm not going to grade it (not that I usually grade things anyway).

Preparation:

Switch your current working directory to my stupid directory with

cd  /home/rebelsky/Web/Courses/CS362/2004S/Examples/stupid

Background

Stupid, Sam's Totally Unintelligible Programing Instruction Doohicky, is a sample programming language I've written as an example of various issues we've discussed in class. You've explored aspects of Stupid earlier this semester.

Today you will examine a translator that turns STUPID programs into PAL programs. You may want to review the lab on PAL for more details of PAL and Stupid.

Exercises

Exercise 1: Stupid Basics

The goal of exercise 1 is to have you consider the form of the generated code and how that code relates to the original program.

a. Scan through the programs in the Examples subdirectory. See if you can determine what each one should do.

b. Execute each in turn with

% java stupid.Stupid Examples/____.stupid

Exercise 2: Translating Boolean Expressions

The goal of exercise 2 is to have you look more closely at code generation.

a. Look at StupidTranslator.java. How does the translation of Boolean expressions differ from the translation discussed in class?

b. Consider the following two uses of the Boolean expression x <> y

• b := x <> y
• if (x <> y) then b := true else b:= false;

i. How might the generated code differ between the two?

ii. What happens when you try to compile the two?

iii. Why do you get different results?

Exercise 3: Adding Operations

One purpose of this part is to have you think more about the steps in translation. A second is to give you experience extending the translator.

Update the translateExpression method in StupidTranslator.java to handle subtraction and division in addition to addition and multiplication.

Test your changes.

Exercise 4: Adding Comparison Operations

The purpose of this part is to have you think more carefully about the translation of Booleans.

In Exercise 2, you observed that the translator cannot handle comparisons used in assignment statements. Update translateExpression so that it handles comparisons.

Exercise 5: Adding Boolean Operations

The purpose of this part is to have you think more carefully about the translation of Booleans.

Update translateBooleanExpression to handle ands and ors.