Assignment 4 and Dupe polish.

www/assignments.scrbl

@@ -6,4 +6,4 @@
 @include-section{assignments/1.scrbl}
 @include-section{assignments/2.scrbl}
 @include-section{assignments/3.scrbl}
-
+@include-section{assignments/4.scrbl}

www/assignments/3.scrbl

@@ -173,6 +173,7 @@ which are defined as:
 ;; | 'add1
 ;; | 'sub1
 ;; | 'zero?
+;; | 'if
 ;; | 'cond
 ;; | 'else
 ;; | 'abs

www/assignments/4.scrbl

@@ -0,0 +1,354 @@
+#lang scribble/manual
+@title[#:tag "Assignment 4" #:style 'unnumbered]{Assignment 4: Let there be Variables, Characters}
+
+@(require (for-label (except-in racket ...)))
+@(require "../notes/fraud-plus/semantics.rkt")
+@(require redex/pict)
+
+@(require "../notes/ev.rkt")
+
+@bold{Due: Thurs, Sept 26, 11:59PM}
+
+@(define repo "https://classroom.github.com/a/HuBPd1o9")
+
+The goal of this assignment is to extend a compiler with binding forms
+and a character data type.
+
+Assignment repository:
+@centered{@link[repo repo]}
+
+You are given a repository with a starter compiler similar to the
+@seclink["Fraud"]{Fraud} language we studied in class.  You are tasked
+with:
+
+@itemlist[
+
+@item{incorporating the Con+ features you added in
+@seclink["Assignment 3"]{Assignment 3},}
+
+@item{extending the language to include a character data type,}
+
+@item{extending the @racket[let]-binding form of the language to bind
+any number of variables, and}
+
+@item{updating the parser to work for Fraud+.}
+
+]
+
+@section[#:tag-prefix "a4-" #:style 'unnumbered]{From Con+ to Fraud+}
+
+Implement the @racket[abs] and unary @racket[-] operations and the
+@racket[cond] form from @seclink["Assignment 3"]{Con+}.  You can start
+from your previous code, but you will need to update it to work for
+Fraud+.
+
+In particular, functions should signal an error when applied to the
+wrong type of argument and your @racket[cond] form should work with
+@emph{arbitrary} question expressions.  In other words, @racket[cond]
+should work like @racket[if] in @seclink["Dupe"]{Dupe}.
+
+The formal semantics of @racket[cond] are defined as:
+
+@(define ((rewrite s) lws)
+   (define lhs (list-ref lws 2))
+   (define rhs (list-ref lws 3))
+   (list "" lhs (string-append " " (symbol->string s) " ") rhs ""))
+
+@(require (only-in racket add-between))
+@(define-syntax-rule (show-judgment name i j)
+   (with-unquote-rewriter
+      (lambda (lw)
+        (build-lw (lw-e lw) (lw-line lw) (lw-line-span lw) (lw-column lw) (lw-column-span lw)))
+      (with-compound-rewriters (['+ (rewrite '+)]
+                                ['- (rewrite '–)]
+                                ['= (rewrite '=)]
+				['!= (rewrite '≠)])
+        (apply centered
+	   (add-between 
+             (build-list (- j i)
+	                 (λ (n) (begin (judgment-form-cases (list (+ n i)))
+	                               (render-judgment-form name))))
+             (hspace 4))))))
+
+@(show-judgment 𝑭-𝒆𝒏𝒗 0 1)
+@(show-judgment 𝑭-𝒆𝒏𝒗 1 2)
+@(show-judgment 𝑭-𝒆𝒏𝒗 2 3)
+
+
+The following files have already been updated for you:
+@itemlist[
+@item{@tt{ast.rkt}}
+@item{@tt{syntax.rkt}}
+@item{@tt{interp.rkt}}
+]
+
+You will need to modify @tt{compile.rkt} to correctly implement these
+features.
+
+
+@section[#:tag-prefix "a4-" #:style 'unnumbered]{Adding a Bit of Character}
+
+Racket has a Character data type for representing single letters.  A
+Racket character can represent any of the 1,114,112 Unicode
+@link["http://unicode.org/glossary/#code_point"]{code points}.
+
+The way a character is most often written is an octothorp, followed by
+a backslash, followed by the character itself.  So for example the
+character @tt{a} is written @racket[#\a].  The character @tt{λ} is
+written @racket[#\λ].  The character @tt{文} is written @racket[#\文].
+
+A character can be converted to an integer and @emph{vice versa}:
+
+@ex[
+(char->integer #\a)
+(char->integer #\λ)
+(char->integer #\文)
+(integer->char 97)
+(integer->char 955)
+(integer->char 25991)
+]
+
+However, integers in the range of valid code points are acceptable to
+@racket[integer->char] and using any other integer will produce an
+error:
+
+@ex[
+(eval:error (integer->char -1))
+(eval:error (integer->char 55296))
+]
+
+There are a few other ways to write characters (see the Racket
+@link["https://docs.racket-lang.org/reference/reader.html#%28part._parse-character%29"]{Reference}
+for the details), but you don't have to worry much about this since
+the lexer takes care of reading characters in all their different
+forms and the run-time system given to you takes care of printing
+them.
+
+Your job is extend the compiler to handle the compilation of
+characters and implement the operations @racket[integer->char],
+@racket[char->integer], and @racket[char?].  The operations should
+work as in Racket and should signal an error (i.e. @racket['err])
+whenever Racket produces an error.  While you're at it, implement
+the predicates @racket[integer?] and @racket[boolean?], too.
+
+The following files have already been updated for you:
+
+@itemlist[
+
+@item{@tt{ast.rkt}}
+
+@item{@tt{syntax.rkt}}
+
+@item{@tt{interp.rkt}}
+
+@item{@tt{main.c}}
+
+]
+
+You will need to modify @tt{compile.rkt} to correctly implement these
+features.  Note that you must use the same representation of
+characters as used in the run-time system and should not change
+@tt{main.c}.
+
+@section[#:tag-prefix "a4-" #:style 'unnumbererd]{Generalizing Let}
+
+The Fraud language has a let form that binds a single variable in the
+scope of some expression.  This is a restriction of the more general
+form of @racket[let] that binds any number of expressions.  So for
+example,
+
+@racketblock[
+(let ((x 1) (y 2) (z 3))
+  _e)
+]
+
+simultaneously binds @racket[x], @racket[y], and @racket[z] in the
+scope of @racket[_e].
+
+The syntax of a @racket[let] expression allows any number of binders
+to occur, so @racket[(let () _e)] is valid syntax and is equivalent to
+@racket[_e].
+
+The binding of each variable is only in scope in the body, @bold{not}
+in the right-hand-sides of any of the @racket[let].
+
+For example, @racketblock[(let ((x 1) (y x)) 0)] is a syntax error
+because the occurrence of @racket[x] is not bound.
+
+The following files have already been updated for you:
+
+@itemlist[
+
+@item{@tt{ast.rkt}}
+
+@item{@tt{interp.rkt}}
+
+]
+
+Update @tt{syntax.rkt} to define two functions:
+
+@itemize[
+
+@item{@code[#:lang "racket"]{expr? ; Any -> Boolean}, which consumes
+anything and determines if it is a well-formed expression, i.e. it
+must be an instance of an @tt{Expr} @emph{and} each @racket[let]
+expression must bind a distinct set of variables.}
+
+@item{@code[#:lang "racket"]{closed? ; Expr -> Boolean}, which consumes
+an @tt{Expr} and determines if it is closed, i.e. every variable
+occurrence is bound.}
+
+]
+
+Update @tt{compile.rkt} to correctly compile the generalized form of
+@racket[let].  The compiler may assume the input is a closed
+expression.
+
+@section[#:tag-prefix "a4-" #:style 'unnumbered]{Extending your Parser}
+
+
+Extend your Con+ parser for the Fraud+ language based on the following
+grammar:
+
+@verbatim{
+<expr> ::= integer
+        |  character
+	|  variable
+        |  ( <compound> )
+	|  [ <compound> ]
+
+<compound> ::= <prim> <expr>
+            |  if <expr> <expr> <expr>
+            |  cond <clause>* <else>
+	    |  let <bindings> <expr>
+
+<prim> ::= add1 | sub1 | abs | - | zero? | integer->char | char->integer
+        |  char? | integer? | boolean?
+
+<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 @tt{lex.rkt}, which provides two
+functions: @racket[lex-string] and @racket[lex-port], which consume a
+string or an input port, respectively, and produce a list of tokens,
+which are defined as follows:
+
+@margin-note{Note that the @tt{Token} type has changed slightly from
+@secref{Assignment 3}: @racket['add1] is now @racket['(prim add1)],
+@racket['cond] is now @racket['(keyword cond)], etc.}
+
+@#reader scribble/comment-reader
+(racketblock
+;; type Token =
+;; | Integer
+;; | Char
+;; | Boolean
+;; | `(variable ,Variable)
+;; | `(keyword ,Keyword)
+;; | `(prim ,Prim)
+;; | 'lparen    ;; (
+;; | 'rparen    ;; )
+;; | 'lsquare   ;; [
+;; | 'rsquare   ;; ]
+;; | 'eof       ;; end of file
+
+;; type Variable = Symbol (other than 'let, 'cond, etc.)
+
+;; type Keyword =
+;; | 'let
+;; | 'cond
+;; | 'else
+;; | 'if
+
+;; type Prim =
+;; | 'add1
+;; | 'sub1
+;; | 'zero?
+;; | 'abs
+;; | '-
+;; | 'integer->char
+;; | 'char->integer
+;; | 'char?
+;; | 'boolean?
+;; | 'integer?
+)
+
+The lexer will take care of reading the @tt{#lang racket} header and
+remove any whitespace.
+
+You must complete the code in @tt{parse.rkt} to implement the parser
+which constructs an s-expression representing a valid Fraud+
+expression, if possible, from a list of tokens.  The @racket[parse]
+function should have the following signature and must be provided by
+the module:
+
+@#reader scribble/comment-reader
+(racketblock
+;; parse : [Listof Token] -> Expr
+)
+
+As an example, @racket[parse] should produce @racket['(add1 (sub1 7))]
+if given
+
+@racketblock['(lparen (prim add1) lparen (prim sub1) 7 rparen rparen eof)]
+
+
+You should not need to make any changes to @tt{lex.rkt}.
+
+The given @tt{interp-file.rkt} and @tt{compile-file.rkt} code no
+longer use @racket[read], but instead use the parser.  This means you
+neither will work until the parser is complete.
+
+
+@bold{The code you are given includes two(!) implementations of the
+Con+ parser.}  One implementation follows the imperative approach; the
+other follows the functional approach.
+
+You may extend either, or you may throw out the given code and start
+from the code you wrote previously.
+
+
+@section[#:tag-prefix "a4-" #:style 'unnumbered]{Testing}
+
+You can test your code in several ways:
+
+@itemlist[
+
+ @item{Using the command line @tt{raco test .} from
+  the directory containing the repository to test everything.}
+
+ @item{Using the command line @tt{raco test <file>} to
+  test only @tt{<file>}.}
+
+ @item{Pushing to github. You can 
+  see test reports at:
+  @centered{@link["https://travis-ci.com/cmsc430/"]{
+    https://travis-ci.com/cmsc430/}}
+
+  (You will need to be signed in in order see results for your private repo.)}]
+
+Note that only a small number of tests are given to you, so you should
+write additional test cases.
+
+@bold{We have removed @tt{random.rkt}} and instead provide a
+@tt{random-exprs.rkt} module which provides @racket[exprs], a list
+of 500 closed expressions.  It is used in the
+@tt{test/compile-rand.rkt} file to randomly test compiler correctness.
+This should help speed up the testing process since the random
+generation is slow.
+
+@section[#:tag-prefix "a4-" #:style 'unnumbered]{Submitting}
+
+Pushing your local repository to github ``submits'' your work.  We
+will grade the latest submission that occurs before the deadline.
+