Revert "Adjusted spec of For-In to insist on Iterable (#291)"

This reverts commit 20087c8.

Author: eernstg

specification/dartLangSpec.tex

@@ -24,9 +24,7 @@
 
 % CHANGES
 % =======
-%
 % Significant changes to the specification.
-%
 % 2.2
 % - Specify whether the values of literal expressions override Object.==.
 % - Allow Type objects as case expressions and const map keys.
@@ -38,8 +36,6 @@
 %   Function.
 % - Generalize specification of type aliases such that they can denote any
 %   type, not just function types.
-% - Added requirement that the iterator of a for-in statement must have
-%   type `Iterator`.
 %
 % 2.1
 % - Remove 64-bit constraint on integer literals compiled to JavaScript numbers.
@@ -12291,33 +12287,24 @@ \subsubsection{For-in}
 \LMLabel{for-in}
 
 \LMHash{}%
-Let $D$ be derived from \syntax{<finalConstVarOrType>?}.
-A for statement of the form \code{\FOR{} ($D$ \id{} \IN{} $e$)\,\,$S$}
-is then treated as the following code,
-where $\id_1$ and $\id_2$ are fresh identifiers:
+Let $D$ be derived from \syntax{<finalConstVarOrType>?}
+and let $n0$ be an identifier that does not occur anywhere in the program.
+A for statement of the form \code{\FOR{} ($D$ \id{} \IN{} $e$) $s$} is equivalent to the following code:
 
 \begin{normativeDartCode}
-$T$ $\id_1$ = $e$;
-\VAR{} $\id_2$ = $id_1$.iterator;
-\WHILE{} ($\id_2$.moveNext()) \{
-\ \ $D$ \id{} = $\id_2$.current;
-\ \ $S$
+\VAR{} $n0$ = $e$.iterator;
+\WHILE{} ($n0$.moveNext()) \{
+\ \ $D$ \id{} = $n0$.current;
+\ \ $s$
 \}
 \end{normativeDartCode}
 
-\noindent
-If the static type of $e$ is a top type
-(\ref{superBoundedTypes})
-then $T$ is \code{Iterable<dynamic>},
-otherwise $T$ is the static type of $e$.
-It is a compile-time error if $T$ is not assignable to \code{Iterable<dynamic>}.
-
-\commentary{
-It follows that it is a compile-time error
-if $D$ is empty and \id{} is a final variable;
-and it is a dynamic error if $e$ has a top type,
-but $e$ evaluates to an instance of a type
-which is not a subtype of \code{Iterable<dynamic>}.
+For purposes of static typechecking,
+this code is checked under the assumption that $n0$ is declared to be of type $T$,
+where $T$ is the static type of \code{$e$.iterator}.
+
+\commentary{
+It follows that it is a compile-time error if $D$ is empty and \id{} is a final variable.
 }