Merge pull request #13 from dvanhorn/next

Update schedule to reflect reality.

Author: dvanhorn

.travis.yml

@@ -8,7 +8,7 @@ env:
   - PANDOC=~/.pandoc
   - PANDOC_DEB="https://github.com/jgm/pandoc/releases/download/2.7.3/pandoc-2.7.3-1-amd64.deb"
   matrix:
-  - RACKET_VERSION=7.3
+  - RACKET_VERSION=7.4
 cache:
   directories:
     - $PANDOC
@@ -46,4 +46,4 @@ deploy:
   script: rsync -rvzp $TRAVIS_BUILD_DIR/www/cmsc430 dvanhorn@junkfood.cs.umd.edu:$WWW_DIR/fall2019
   on:
     branch: master
-    condition: "$RACKET_VERSION='7.3'"
+

www/notes/con.scrbl

@@ -56,12 +56,17 @@ Let's consider some examples:
 
 @itemlist[
 
-@item{...}
+@item{@racket['(if (zero? 0) (add1 2) 4)] means @racket[3].}
+@item{@racket['(if (zero? 1) (add1 2) 4)] means @racket[4].}
+@item{@racket['(if (zero? (if (zero? (sub1 1)) 1 0)) (add1 2) 4)] means @racket[4].}
+@item{@racket['(if (zero? (add1 0)) (add1 2) (if (zero? (sub1 1)) 1 0))] means @racket[1].}
 
 ]
 
 
-The semantics...
+The semantics is inductively defined as before.  There are @emph{two}
+new rules added for handling if-expressions: one for when the test
+expression means @racket[0] and one for when it doesn't.
 
 @(define ((rewrite s) lws)
    (define lhs (list-ref lws 2))
@@ -135,33 +140,96 @@ according to @render-term[C 𝑪𝒓]:
 @(show-judgment 𝑪 0 1)
 }
 
-The interpreter ...
+The interpreter has an added case for if-expressions, which
+recursively evaluates the test expression and branches based on its
+value.
 
 @codeblock-include["con/interp.rkt"]
 
 We can confirm the interpreter computes the right result for the
 examples given earlier:
 
 @ex[
-'...
+(interp '(if (zero? 0) (add1 2) 4))
+(interp '(if (zero? 1) (add1 2) 4))
+(interp '(if (zero? (if (zero? (sub1 1)) 1 0)) (add1 2) 4))
+(interp '(if (zero? (add1 0)) (add1 2) (if (zero? (sub1 1)) 1 0)))
 ]
 
-Correctness...
-@;{
-@bold{Interpreter Correctness}: @emph{For all Con expressions
-@racket[e] and integers @racket[i], if (@racket[e],@racket[i]) in
-@render-term[C 𝑪], then @racket[(interp e)] equals
-@racket[i].}
-}
+The argument for the correctness of the interpreter follows the same
+structure as for @seclink["Blackmail"]{Blackmail}, but with an added case for
+if-expressions.
 
 @section{An Example of Con compilation}
 
 Suppose we want to compile @racket['(if (zero? 8) 2 3)]...
 
-We already know how to compile the @racket['8], @racket['2], and
-@racket['3] part.
+We already know how to compile the @racket[8], @racket[2], and
+@racket[3] part.
+
+What needs to happen?
+
+@itemlist[
+@item{Execute the code for @racket[8] leaving the result in @racket['rax],}
+@item{check whether @racket['rax] holds zero,}
+@item{if it does, execute the code for @racket[2],}
+@item{if it doesn't, execute the code for @racket[3].}
+]
+
+We can determine whether @racket[8] evaluates to @racket[0] using a
+comparison instruction: @racket['(cmp rax 0)].  To do the conditional
+execution, we will need to jump to different parts of the code to
+either execute the code for @racket[2] or @racket[3].  There are
+several ways we could accomplish this, but we take the following
+approach: immediately after the comparison, do a conditional jump to
+the code for the else branch when non-zero. Should the jump not occur,
+the next instructions will carry out the evaluation of the then
+branch, then (unconditionally) jump over the else branch code.
+
+To accomplish this, we will need two new labels: one for the else
+branch code and one for the end of the else branch code.  The
+@racket[gensym] function can be used to generate symbols that have not
+appeared before.
+
+In total, the code for this example would look like:
+
+@racketblock[
+'((mov rax 8)
+  (cmp rax 0)
+  (jne if-else-begin)
+  (mov rax 2)
+  (jmp if-else-end)
+  if-else-begin
+  (mov rax 3)
+  if-else-end)
+]
+
+Notice that the @racket['(mov rax 8)], @racket['(mov rax 3)] and
+@racket['(mov rax 2)] parts are just the instructions generated by
+compiling @racket[8], @racket[2] and @racket[3].  Generalizing from
+this, we arrive at the following code for the compiler:
+
+@racketblock[
+(let ((c0 (compile-e e0))
+      (c1 (compile-e e1))
+      (c2 (compile-e e2))
+      (l0 (gensym "if-else-begin"))
+      (l1 (gensym "if-else-end")))
+  '(,@c0
+    (cmp rax 0)
+    (jne ,l0)
+    ,@c1
+    (jmp ,l1)
+    ,l0
+    ,@c2
+    ,l1))
+]
+
+
+@ex[
+(asm-display (compile '(if (zero? 8) 2 3)))
+]
 
-What needs to happen? ...
 
 @codeblock-include["con/asm/ast.rkt"]
 

www/notes/con/compile.rkt

@@ -22,27 +22,14 @@
     [`(if (zero? ,e0) ,e1 ,e2)
      (let ((c0 (compile-e e0))
            (c1 (compile-e e1))
-           (c2 (compile-e e2)))
-       (match (gen-if-labels)
-         [(list if-f if-x)
-          `(,@c0
-            (cmp rax 0)
-            (jne ,if-f)
-            ,@c1
-            (jmp ,if-x)
-            ,if-f
-            ,@c2
-            ,if-x)]))]))
-
-;; -> [List Label Label]
-;; Guaranteed to be unique on each call
-(define gen-if-labels
-  (let ((i 0))
-    (λ ()
-      (set! i (add1 i))
-      (list (lab "f" i)
-            (lab "x" i)))))
-
-;; String Integer -> Symbol
-(define (lab s i)
-  (string->symbol (string-append "if_" s "_" (number->string i))))
+           (c2 (compile-e e2))
+           (l0 (gensym "if"))
+           (l1 (gensym "if")))
+       `(,@c0
+         (cmp rax 0)
+         (jne ,l0)
+         ,@c1
+         (jmp ,l1)
+         ,l0
+         ,@c2
+         ,l1))]))

www/schedule.scrbl

@@ -21,26 +21,26 @@
                (list @wk{9/3}
 	       	     @seclink["Assignment 1"]{A1}
                      @elem{@secref["OCaml to Racket"] (cont.)}
-                     @secref["Abscond"])
+                     @itemlist[@item{@secref["Abscond"]} @item{@secref["Blackmail"]}])
 
                (list @wk{9/10}
-	       	     "A2" @;seclink["Assignment 2"]{A2}
-                     @secref["Blackmail"]
-                     @secref["Con"])
+	       	     @seclink["Assignment 2"]{A2}
+                     @secref["Con"]
+		     @secref["Dupe"])
 
                (list @wk{9/17}
-	       	     "A3" @;seclink["Assignment 3"]{A3}
-                     @secref["Dupe"]
-                     @secref["Extort"])
+	       	     "A3" @;seclink["Assignment 3"]{A3}                     
+                     @secref["Extort"]
+                     @secref["Fraud"])
 
                (list @wk{9/24}
 	       	     "A4" @;seclink["Assignment 4"]{A4}
-                     @secref["Fraud"]
-                     @secref["Grift"])
+                     @secref["Grift"]
+		     @secref["Hustle"])
 
                (list @wk{10/1}
 	       	     "A5" @;seclink["Assignment 5"]{A5}                     
-                     @secref["Hustle"]
+                     @elem{TBD}
                      'cont)
 
                (list @wk{10/8}