wibbles

book.tex

@@ -13342,15 +13342,17 @@ kind of sequence.
 
 \begin{ocamlx}
   For this challenge, you will implement \LangArray{}, a variant of \LangFun{}
-  supporting arrays. Unlike previous chapters, all that will provided to you
-  are the concrete input grammar for \LangArray{} and
+  supporting arrays. Unlike previous chapters, all that will be provided to you
+  are a specification of the concrete input grammar for \LangArray{} and
   an improved version of \code{runtime.c} that supports garbage collection of
   arrays (according to a particular specified memory layout convention).
   It is up to you to produce appropriately modified versions of \code{RFun.ml}, \code{CFun.ml},
   and \code{X86Fun.ml}, as well as the passes that glue them together, which you should
-  put in a file \code{Chapter9Arrays.ml}. You have complete freedom to add
+  put in a file \code{Chapter9Arrays.ml}. You must implement a type checker for
+  source \LangArray{} programs. Otherwise, you
+  hou have complete freedom to add
   features as needed to the intermediate languages and the set of X86 instructions
-  you use.
+  you use. 
 \end{ocamlx} 
 
 The Racket language does not distinguish between tuples and arrays,
@@ -13377,7 +13379,8 @@ inner-product of two arrays (Figure~\ref{fig:inner-product}).
 \begin{itemize}
   \item An array is created with \code{(array $e_1$ $e_2$)} where $e_1$ evaluates
     to an integer representing the length of the array, and $e_2$ evaluates to the
-    initial value to be used for each array element.  
+    initial value to be used for all the array elements. (Note that $e_2$ is evaluated
+    just once per array creation, not once per element!)
   \item The length of an array is returned by \code{(len $e$)} where $e$ evaluates to an array.
   \item Reading from the array is denoted by \code{(@ $e_1$ $e_2$)} where $e_1$ evaluates to an
     array and $e_2$ evaluates to an integer index into the array (counting from 0).