Assignment 3: Static Semantics

Due: class time (1:30), Tuesday, October 11.

Project 3 is to read chapter five of the text and build a static-semantics checker for Appel's Tiger language.

Your code should perform the static semantic checks decribed in Chapter 5:

type-check the program
check for "break" statements that occur out of scope.

Your semant module should export a function with this signature:

transProg : Absyn.exp -> unit

that checks an AST and outputs error messages if anything is wrong. (Why is our type-checker called transProg rather than something like typeCheck? Because we'll be extending it in project 4 to type-check and translate the AST to our intermediate representation.)

You will find a structure Types defining a datatype to represent Tiger types in $TIGER/chap5/types.sml.

You should submit:

A semant.sml file containing your code
Any other source files you wrote to support your checker
Your sources.cm file
A text file describing
- The members of your team
- Anything you think is of interest about your code.

Words to the wise:

Appel's advice on pages 121/122 about breaking the the work into a part A and a part B is good advice.
One thing I found confusing when I wrote my checker was the fact that there are two "ty" types:

Types.ty
These are semantic values -- they represent the various types found in Tiger. This is carefully designed to assist the type-checking process, e.g. handling circularities.
Absyn.ty
These are syntactic values -- they represent the notation in Tiger for describing types.

Obviously, we can map any Absyn.ty chunk of Tiger type syntax to a Types.ty value. But don't confuse the two different datatypes. Anytime you must handle a description of a Tiger type, be clear in your mind: are you handling a semantic value or a chunk of syntax?
This is a significant piece of code. I found it harder than the parser as a straight-up programming effort. Start now.

-Olin

CS4240