Add an intermezzo about the id function.

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

diff --git a/Chapters/Prototype.tex b/Chapters/Prototype.tex
index 3d8fb678c23406138162f1ac3fdc4affb5ccc21b..b391d4fcbc6951c2c86af451b805cec8187aae28 100644 (file)
--- a/Chapters/Prototype.tex
+++ b/Chapters/Prototype.tex
@@ -622,14 +622,6 @@
 
       The value of a cast is the value of its body, unchanged. The type of this
       value is equal to the target type, not the type of its body.
-
-      \todo{Move and update this paragraph}
-      Note that this syntax is also used sometimes to indicate that a particular
-      expression has a particular type, even when no cast expression is
-      involved. This is then purely informational, since the only elements that
-      are explicitly typed in the Core language are the binder references and
-      cast expressions, the types of all other elements are determined at
-      runtime.
     \stopdesc
 
     \startdesc{Note}
@@ -685,6 +677,22 @@
       families and other non-standard Haskell stuff which we do not (plan to)
       support.
 
+      \placeintermezzo{}{
+        \startframedtext[width=8cm,background=box,frame=no]
+        \startalignment[center]
+          {\tfa The \hs{id} function}
+        \stopalignment
+        \blank[medium]
+          A function that is probably present in every functional language, is
+          the \emph{identity} function. This is the function that takes a
+          single argument and simply returns it unmodified. In Haskell this
+          function is called \hs{id} and can take an argument of any type
+          (\ie, it is polymorphic).
+
+          The \hs{id} function will be used in the examples every now and
+          then.
+        \stopframedtext
+      }
       In Core, every expression is typed. The translation to Core happens
       after the typechecker, so types in Core are always correct as well
       (though you could of course construct invalidly typed expressions