Add Scrutinee binder removal.

[matthijs/master-project/report.git] / Chapters / Normalization.tex

diff --git a/Chapters/Normalization.tex b/Chapters/Normalization.tex
index e1a96ff0c396a10239ec8b8330fc5f62064844d5..2768ba2c0a2c89e87e989471bd5d7a3c53ea5e4c 100644 (file)
--- a/Chapters/Normalization.tex
+++ b/Chapters/Normalization.tex
@@ -1502,6 +1502,46 @@
           \stopframedtext
         }
 
           \stopframedtext
         }
 

+      \subsubsection{Scrutinee binder removal}
+        This transformation removes (or rather, makes wild) the binder to
+        which the scrutinee is bound after evaluation. This is done by
+        replacing the bndr with the scrutinee in all alternatives. To prevent
+        duplication of work, this transformation is only applied when the
+        scrutinee is already a simple variable reference (but the previous
+        transformation ensures this will eventually be the case). The
+        scrutinee binder itself is replaced by a wild binder (which is no
+        longer displayed).
+
+        Note that one could argue that this transformation can change the
+        meaning of the Core expression. In the regular Core semantics, a case
+        expression forces the evaluation of its scrutinee and can be used to
+        implement strict evaluation. However, in the generated \VHDL,
+        evaluation is always strict. So the semantics we assign to the Core
+        expression (which differ only at this particular point), this
+        transformation is completely valid.
+
+        \starttrans
+        case x of bndr
+          alts
+        -----------------        \lam{x} is a local variable reference
+        case x of
+          alts[bndr=>x]
+        \stoptrans
+
+        \startbuffer[from]
+        case x of y
+          True -> y
+          False -> not y
+        \stopbuffer
+
+        \startbuffer[to]
+        case x of
+          True -> x
+          False -> not x
+        \stopbuffer
+
+        \transexample{scrutbndrremove}{Scrutinee binder removal}{from}{to}
+

       \subsubsection{Case normalization}
         This transformation ensures that all case expressions get a form
         that is allowed by the intended normal form. This means they
       \subsubsection{Case normalization}
         This transformation ensures that all case expressions get a form
         that is allowed by the intended normal form. This means they