Revision of assign 3 and 4.

Assignment 3 has been split into two assignments (3 & 4 now).  The
first does new primitives and cond.  The second does case.  This
change updates the descriptions to reflect the new structure.

Author: dvanhorn

www/assignments/3.scrbl

@@ -8,17 +8,15 @@
 
 The goal of this assignment is to extend the language developed in
 @secref{Dupe} with some simple unary numeric and boolean operations
-and two forms of control flow expressions: @racket[cond]-expressions
-and @racket[case]-expressions.
+and a new form of control flow expressions: @racket[cond]-expressions.
 
-@section[#:tag-prefix "a3-" #:style 'unnumbered]{Dupe+}
+@section[#:tag "a3-dupe-plus" #:style 'unnumbered]{Dupe+}
 
 The Dupe+ language extends Dupe in the follow ways:
 
 @itemlist[
 @item{adding new primitive operations,}
-@item{adding @racket[cond], and}
-@item{adding @racket[case].}
+@item{adding @racket[cond].}
 ]
 
 @subsection[#:tag-prefix "a3-" #:style 'unnumbered]{Primitives}
@@ -27,7 +25,7 @@ The following new primitves are included in Dupe+:
 
 @itemlist[
 @item{@racket[(abs _e)]: compute the absolute value of @racket[_e],}
-@item{@racket[(- _e)]: flips the sign of @racket[_e], i.e. compute @math{0-@racket[_e]}, and}
+@item{@racket[(- _e)]: flip the sign of @racket[_e], i.e. compute @math{0-@racket[_e]}, and}
 @item{@racket[(not _e)]: compute the logical negation of @racket[_e]; note that the negation of @emph{any} value other than @racket[#f] is @racket[#f] and the negation of @racket[#f] is @racket[#t].}
 ]
 
@@ -42,10 +40,10 @@ The following new conditional form is included in Dupe+:
 ]
 
 A @racket[cond] expression has any number of clauses @racket[[_e-pi
-_e-ai] ...], followed by an ``else'' clause @racket[[else _en]].  For
-the purposes of this assignment, we will assume every @racket[cond]
-expression ends in an @racket[else] clause, even though this is not
-true in general for Racket.  The parser should reject any
+_e-ai] ...], followed by an ``else'' clause @racket[[else _e-an]].
+For the purposes of this assignment, we will assume every
+@racket[cond] expression ends in an @racket[else] clause, even though
+this is not true in general for Racket.  The parser will reject any
 @racket[cond]-expression that does not end in @racket[else].
 
 
@@ -56,43 +54,65 @@ does not evaluate to @racket[#f] is found, in which case, the corresponding expr
 @racket[cond] expression.  If no such @racket[_e-pi] exists, the
 expression @racket[_e-an]'s value is the value of the @racket[cond].
 
-@subsection[#:tag-prefix "a3-" #:style 'unnumbered]{Case expressions}
 
-The following new case form is included in Dupe+:
+@section[#:tag-prefix "a3-" #:style 'unnumbered]{Implementing Dupe+}
 
-@racketblock[
-(case _ev
-      [(_d1 ...) _e1]
-      ...
-      [else _en])
-]
+You must extend the interpreter and compiler to implement Dupe+. (The
+parser for Dupe+ is given to you.)  You are given a file
+@tt{dupe-plus.zip} on ELMS with a starter compiler based on the
+@secref{Dupe} language we studied in class.
 
-The @racket[case] expression form is a mechanism for dispatching
-between a number of possible expressions based on a value, much like
-C's notion of a @tt{switch}-statement.
+You may use any a86 instructions you'd like, however it is possible to
+complete the assignment using @racket[Cmp], @racket[Je], @racket[Jg],
+@racket[Jmp], @racket[Label], @racket[Mov], and @racket[Sub].
 
-The meaning of a @racket[case] expression is computed by evaluating
-the expression @racket[_ev] and then proceeding in order through each
-clause until one is found that has a datum @racket[_di] equal to
-@racket[_ev]'s value.  Once such a clause is found, the corresponding
-expression @racket[_ei] is evaluated and its value is the value of the
-@racket[case] expression.  If no such clause exists, expression
-@racket[_en] is evaluated and its value is the value of the
-@racket[case] expression.
+@section[#:tag-prefix "a3-" #:style 'unnumbered #:tag "parse"]{Parsing Dupe+}
 
-Note that each clause consists of a parenthesized list of
-@emph{datums}, which in the setting of Dupe means either integer or
-boolean literals.
+The AST type and parser for Dupe+ are given to you.
 
-@section[#:tag-prefix "a3-" #:style 'unnumbered]{Implementing Dupe+}
+Here's the AST definition for the added primitives and @racket[cond]:
 
-You must extend the parser, interpreter, and compiler to implement
-Dupe+.  You are given a file @tt{dupe-plus.zip} on ELMS with a starter
-compiler based on the @secref{Dupe} language we studied in class.
+@#reader scribble/comment-reader
+(racketblock
+;; type Expr =
+;; ...
+;; | (Cond [Listof CondClause] Expr)
 
-You may use any a86 instructions you'd like, however it is possible to
-complete the assignment using @racket[Cmp], @racket[Je], @racket[Jg],
-@racket[Jmp], @racket[Label], @racket[Mov], and @racket[Sub].
+;; type CondClause = (Clause Expr Expr)
+
+;; type Op = 
+;; ...
+;; | 'abs | '- | 'not
+
+(struct Cond (cs e)    #:prefab)
+(struct Clause (p b)   #:prefab)
+)
+
+There is one new kind of expression constructor: @racket[Cond].  A
+@racket[Cond] AST node contains a list of cond-clauses and expression,
+which the expression of the @racket[else] clause.  Each cond-clause is
+represented by a @racket[Clause] structure containing two expressions:
+the left-hand-side of the clause which is used to determine whether
+the right-hand-side is evaluated, and the right-hand-side expression.
+
+Here are some examples of how concrete expressions are parsed into
+ASTs using this representation:
+
+@itemlist[
+
+@item{@racket[(abs 1)] parses as @racket[(Prim1 'abs (Lit 1))],}
+
+@item{@racket[(not #t)] parses as @racket[(Prim1 'not (Lit #t))],}
+
+@item{@racket[(cond [else 5])] parses as @racket[(Cond '() (Lit 5))],}
+
+@item{@racket[(cond [(not #t) 3] [else 5])] parses as @racket[(Cond
+(list (Clause (Prim1 'not (Lit #t)) (Lit 3))) (Lit 5))],}
+
+@item{@racket[(cond [(not #t) 3] [7 4] [else 5])] parses as
+@racket[(Cond (list (Clause (Prim1 'not (Lit #t)) (Lit 3)) (Clause
+(Lit 7) (Lit 4))) (Lit 5))],}
+]
 
 @subsection[#:tag-prefix "a3-" #:style 'unnumbered]{Implementing primitives}
 
@@ -103,8 +123,7 @@ these using the limited a86 instruction set.
 
 To do this, you should:
 @itemlist[
-@item{Study @tt{ast.rkt} and the new forms of expression (i.e. new AST nodes)
-      then update the comment at the top describing what the grammmar should look like.}
+@item{Study @tt{ast.rkt} to understand how these new forms of expression are represented.}
 
 @item{Study @tt{parse.rkt} and add support for parsing these
 expressions. (See @secref[#:tag-prefixes '("a3-")]{parse} for guidance.)}
@@ -126,7 +145,6 @@ To do this, you should:
 
 @itemlist[
 @item{Study @tt{ast.rkt} to add appropriate AST nodes.}
-@item{Extend @tt{parse.rkt} to parse such expressions. (See @secref[#:tag-prefixes '("a3-")]{parse} for guidance.)}
 @item{Update @tt{interp-prim.rkt} and @tt{interp.rkt} to correctly interpret @racket[cond] expressions.}
 
 @item{Make examples of @racket[cond]-expressions and potential translations of them
@@ -138,108 +156,6 @@ expressions based on your examples.}
 @item{Check your implementation by running the tests in @tt{test/all.rkt}.}
 ]
 
-@section[#:tag-prefix "a3-" #:style 'unnumbered]{Implementing case}
-
-Implement the @racket[case] expression form as described earlier.
-To do this, you should:
-
-@itemlist[
-@item{Study @tt{ast.rkt} to add appropriate AST nodes.}
-@item{Extend @tt{parse.rkt} to parse such expressions. (See @secref[#:tag-prefixes '("a3-")]{parse} for guidance.)}
-@item{Update @tt{interp-prim.rkt} and @tt{interp.rkt} to correctly interpret @racket[case] expressions.}
-
-@item{Make examples of @racket[case]-expressions and potential translations of them
-to assembly.}
-
-@item{Update @tt{compile.rkt} to correctly compile @racket[case] expressions based on your examples.}
-
-@item{Check your implementation by running the tests in @tt{test/all.rkt}.}
-]
-
-@section[#:tag-prefix "a3-" #:style 'unnumbered #:tag "parse"]{A Leg Up on Parsing}
-
-In the past, designing the AST type and structure definitions has
-given students some grief.  Getting stuck at this point means you
-can't make any progress on the assignment and making a mistake at this
-level can cause real trouble down the line for your compiler.
-
-For that reason, let us give you a strong hint for a potential design
-of the ASTs and examples of how parsing could work.  You are not
-required to follow this design, but you certainly may.
-
-Here's a potential AST definition for the added primitives,
-@racket[cond], and @racket[case]:
-
-@#reader scribble/comment-reader
-(racketblock
-;; type Expr =
-;; ...
-;; | (Cond [Listof CondClause] Expr)
-;; | (Case Expr [Listof CaseClause] Expr)
-
-;; type CondClause = (Clause Expr Expr)
-;; type CaseClause = (Clause [Listof Datum] Expr)
-
-;; type Datum = Integer | Boolean
-
-;; type Op = 
-;; ...
-;; | 'abs | '- | 'not
-
-(struct Cond (cs e)    #:prefab)
-(struct Case (e cs el) #:prefab)
-(struct Clause (p b)   #:prefab)
-)
-
-There are two new kinds of expression constructors: @racket[Cond] and
-@racket[Case].  A @racket[Cond] AST node contains a list of
-cond-clauses and expression, which the expression of the @racket[else]
-clause.  Each cond-clause is represented by a @racket[Clause]
-structure containing two expressions: the left-hand-side of the
-clause which is used to determine whether the right-hand-side is
-evaluated, and the right-hand-side expression.
-
-The @racket[Case] AST node contains three things: an expression that
-is the subject of the dispatch (i.e. the expression that is evaluated
-to determine which clause should be taken), a list of case-clauses
-(not to be confused with cond-clauses), and an @racket[else]-clause
-expression.  Each case-clause, like a cond-clause, consists of two
-things.  Hence we re-use the @racket[Clause] structure, but with
-different types of elements.  The first element is a list of
-@emph{datums}, each being either an integer or a boolean.
-
-Now, we won't go so far as to @emph{give} you the code for
-@racket[parse], but we can give you some examples:
-
-@itemlist[
-
-@item{@racket[(abs 1)] parses as @racket[(Prim1 'abs (Lit 1))],}
-
-@item{@racket[(not #t)] parses as @racket[(Prim1 'not (Lit #t))],}
-
-@item{@racket[(cond [else 5])] parses as @racket[(Cond '() (Lit 5))],}
-
-@item{@racket[(cond [(not #t) 3] [else 5])] parses as @racket[(Cond
-(list (Clause (Prim1 'not (Lit #t)) (Lit 3))) (Lit 5))],}
-
-@item{@racket[(cond [(not #t) 3] [7 4] [else 5])] parses as
-@racket[(Cond (list (Clause (Prim1 'not (Lit #t)) (Lit 3)) (Clause
-(Lit 7) (Lit 4))) (Lit 5))],}
-
-@item{@racket[(case (add1 3) [else 2])] parses as @racket[(Case (Prim1
-'add1 (Lit 3)) '() (Lit 2))].}
-
-@item{@racket[(case 4 [(4) 1] [else 2])] parses as @racket[(Case (Lit
-4) (list (Clause (list 4) (Lit 1))) (Lit 2))],}
-
-@item{@racket[(case 4 [(4 5 6) 1] [else 2])] parses as @racket[(Case (Lit
-4) (list (Clause (list 4 5 6) (Lit 1))) (Lit 2))], and}
-
-@item{@racket[(case 4 [(4 5 6) 1] [(#t #f) 7] [else 2])] parses as @racket[(Case (Lit
-4) (list (Clause (list 4 5 6) (Lit 1)) (Clause (list #t #f) (Lit 7))) (Lit 2))].}
-]
-
-
 @section[#:tag-prefix "a3-" #:style 'unnumbered]{Testing}
 
 You can test your code in several ways: