On this page:
From Fraud+   to Hustle+
Strung out
More operations
Extending the Parser
Testing
Submitting
7.4

Assignment 5: A Heap of Characters

Due: Tues, April 28, 11:59PM EST

The goal of this assignment is to extend a compiler with data types that require memory allocation and dereferencing.

Assignment repository:

You are given a repository with a starter compiler similar to the Hustle language we studied in class. You are tasked with:

From Fraud+ to Hustle+

Implement all the features of Fraud+, extended to Hustle+.

Strung out

In the last assignment, you implemented a character data type for representing single letters. In this assignment, you will implement a String data type for representing arbitrarily long sequences of characters.

Strings are disjoint from all other data types and are essentially a fixed-size array of characters. Literal strings are written by enclosing the characters within the string in double quotes ("). Strings can include double quotes by using the escape sequence \".

You must add the following operations to Hustle+:

The run-time system has been updated to account for a string type. It assumes a representation where the length of the string is stored in memory, followed by the characters of the string, in order. You are free to change the representation if you’d like, but you will have to update the run-time system to properly print strings. Otherwise, no changes to the run-time system should be necessary.

If you want to understand the details of how strings are implemented in the run-time system. See the function print_string() in main.c.

More operations

Add the following operations to the Hustle+ language:

Extending the Parser

The parser has been extended from the Fraud+ parser for the Hustle+ language based on the following grammar:

<expr> ::= integer

        |  character

        |  boolean

        |  variable

        |  string

        |  empty

        |  ( <compound> )

        |  [ <compound> ]

 

<compound> ::= <prim1> <expr>

            |  <prim2> <expr> <expr>

            |  - <expr> <maybe-expr>

            |  if <expr> <expr> <expr>

            |  cond <clause>* <else>

            |  let <bindings> <expr>

 

<prim1> ::= add1 | sub1 | abs | zero? | integer->char | char->integer

         |  char? | integer? | boolean? | string? | box? | empty? | cons?

         |  box | unbox | car | cdr | string-length

 

<prim2> ::= make-string | string-ref | = | < | <=

         |  char=? | boolean=? | + | cons

 

<maybe-expr> ::=

              |  <expr>

 

<clause> ::= ( <expr> <expr> )

          |  [ <expr> <expr> ]

 

<else> ::= ( else <expr> )

        |  [ else <expr> ]

 

<bindings> ::= ( <binding>* )

            |  [ <binding>* ]

 

<binding> ::= ( variable <expr> )

           |  [ variable <expr> ]

There is a lexer given to you in lex.rkt, which provides two functions: lex-string and lex-port, which consume a string or an input port, respectively, and produce a list of tokens, which are defined as follows (only the new parts are shown):

; type Token =
; ...
; | '()
; | String
 
; type Prim = Prim1 | Prim2 | '-
 
; type Prim1 =
; | 'add1
; | 'sub1
; | 'zero?
; | 'abs
; | 'integer->char
; | 'char->integer
; | 'char?
; | 'boolean?
; | 'integer?
; | 'string?
; | 'box?
; | 'empty?
; | 'cons?
; | 'box
; | 'unbox
; | 'car
; | 'cdr
; | 'string-length
 
; type Prim2 =
; | 'make-string
; | 'string-ref
; | '=
; | '<
; | '<=
; | 'char=?
; | 'boolean=?
; | '+
; | 'cons

The lexer will take care of reading the #lang racket header and remove any whitespace.

The code in parse.rkt implements the parser which constructs an s-expression representing a valid Hustle+ expression, if possible, from a list of tokens.

As an example, parse should produce '(add1 (sub1 7)) if given

'(lparen (prim add1) lparen (prim sub1) 7 rparen rparen eof)

You should not need to make any changes to lex.rkt or to parse.rkt, but you do need to understand the structure of the resulting AST, which is why the information above was provided.

Testing

You can test your code in several ways:

Note that only a small number of tests are given to you, so you should write additional test cases.

There is separate a repository for tests! The testing set-up is slightly different for this assignment. There is a whole other repository that contains tests. When you push your code, Travis will automatically run your code against the tests. If you would like to run the tests locally, clone the following repository into the directory that contains your compiler and run raco test . to test everything:

https://github.com/cmsc430/assign05-test.git

This repository will evolve as the week goes on, but any time there’s a significant update it will be announced on Piazza.

Submitting

Pushing your local repository to github “submits” your work. We will grade the latest submission that occurs before the deadline.