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Assignment 3: Conditionals: the Cond language

Overview

In this assignment, you will be extending the "Var" language compiler from the last assignment and adding the following features:

  • conditionals (if statements)
  • boolean values (true or false, written as #t and #f)
  • type checking (although you don't have to write the type checking code)

Textbook coverage

This assignment is based on chapter 4 of Essentials of Compilation.

Due date

This assignment is due on Friday, November 8th at 6 PM.

Starting code base

The starting code base is the zipfile ch4.zip, which is posted on the course Canvas site. You should unzip this file in your Github repo, inside the src/ directory. It contains partial implementations of all the code for the assignment.

Inside the ch4 directory will be these familiar subdirectories:

  • The tests/ subdirectory contains the test programs for the compiler.

  • The reference/ subdirectory contains the output from the instructor's version of the compiler.

  • The scripts/ subdirectory contains scripts for testing your code.

README or README.md file

Create a README or README.md file in your ch4 directory, and in it, identify which person wrote which passes. (If both partners worked on a pass, indicate that too.) Also, if you used any late days on the assignment, indicate how many late days you used.

New language features

The new language features are described in the textbook and the lectures, but in brief, they are:

  • a Boolean type
  • boolean values: true (#t) and false (#f)
  • relational operators (operators that return boolean values): eq?, <, <=, >, and >=

  • new expressions:

    • and (boolean AND)
    • or (boolean OR)
    • if (conditionals)

In addition, there is a boolean not operator, the relational operators <, <=, >, and >= which all take two integer operands and return a boolean, and the eq? (equality comparison) operator which takes either two integers or two booleans, and returns a boolean.

Operators no longer have separate intermediate language constructors like Add and Negate from the Var language compiler; all of these have been combined together into the Prim constructor (which stands for "primitive operation") which can take any number of arguments. Checking that each operator receives the right number of arguments is the responsibility of the type checkers.

Type checking

Since this language has two types (Integer and Boolean), it needs a type checker. In fact, two intermediate languages have type checkers: the AST language ("Lif") and the C-like intermediate language ("Cif"). The type checkers are supplied to you in the Type_check, Type_check_lif, and Type_check_cif modules. You will only notice them if your code fails to type check.