Assignment 3: Static Semantics

Due: class time (6 pm), Thursday, March 1.

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:

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. If you wish to use the type lattice I sketched out in my types lecture for your compiler, you will have to extend Andrew's definition to include a "bottom" type (compatible with everything) for the type of break expressions. This will permit your typechecker to pass expressions such as

if y = 0 then break else x / y
x / (if y = 0 then break else y)
a[break] := x
x := break

This is a permitted extension to the compiler. It's not required, however.

You should submit:

Words to the wise: