Assignment 6: Syntax Checking
Due: Tuesday, November 30th, 11:59PM EDT
The goal of this assignment is to add syntax checking to our compiler.
You are given a repository with a starter compiler similar to the Mountebank language we studied in class. You are tasked with:
implementing compile-time syntax checking.
Syntax Checking
Up until now, we’ve written our compiler assuming that programs are well-formed, but there has never been any code that actually checks this assumption. The assumptions go beyond the properties checked during parsing. For example, our parser will happily accept a program like (lambda (x x) x), and the compiler will emit code for it even though this is not a well-formed program.
The idea of this assignment is to implement a function, defined in check-syntax.rkt:
; Prog -> Prog (define (check-syntax p) ...)
If the program is well-formed, it should behave like the identity function, returning the same program it was given as input. On ill-formed programs, it should signal an error using error.
For the purposes of this assignment, the quality of the error messages doesn’t matter, although in real programming language implementations, good error messages are crucial.
Here are the properties that should be checked of each program:
Programs are closed; there are no unbound variables in the program.
Every defined function should have a distinct name.
Every function parameter should be distinct from the other parameters of that function.
Every function’s name should be distinct from all of its parameters’ names.
Every function name and variable should not clash with any of the keywords of our language, e.g. lambda, if, etc. (Note this is not a restriction Racket puts on programs; the following is a perfectly reasonable expression: (λ (λ) λ), but we’ll consider this a syntax error.)
Every pattern variable in a pattern should be distinct. (Racket also allows this, but it has a complicated run-time semantics which we don’t implement so instead we just rule out these programs.)
The starter code calls check-syntax in both compile-file.rkt and interp-file.rkt. The definition of check-syntax is stubbed out in check-syntax.rkt.
There are a few tests included in test/check-syntax.rkt. For this assignment, very few tests are included so you should write your own.
Update a86
There have been some changes to a86 that you’ll need. You can update the langs package with the following:
raco pkg update langs |
Submitting
You should submit on Gradescope. You should submit a zip file that has exactly the same structure that the stub contains. We will only use the check-syntax.rkt files for grading, so make sure all your work is contained there!