Iterators (VirusTotal#1141)

This introduces a change in the way in which "for-in" loops work by introducing the concept of iterators. These kind of loops now accept an iterator that will return a sequence of values. Besides the integer ranges (N..M) and integer enumerations (X,Y,Z), this kind of loops now accepts other kinds of iterables, like arrays. This allows conditions like the following one:

for any section in pe.sections: ( section.name == "foo" )

Until now the same expression was written as:

for any i in (0..pe.number_of_sections - 1): ( pe.sections[i].name == "foo" )

The new syntax is more legible and opens door for more powerful features in the future. Backward compatibility is maintained.

libyara/compiler.c

@@ -174,7 +174,7 @@ YR_API int yr_compiler_create(
   new_compiler->file_name_stack_ptr = 0;
   new_compiler->fixup_stack_head = NULL;
   new_compiler->loop_depth = 0;
-  new_compiler->loop_for_of_mem_offset = -1;
+  new_compiler->loop_for_of_var_index = -1;
   new_compiler->compiled_rules_arena = NULL;
   new_compiler->namespaces_count = 0;
   new_compiler->current_rule = NULL;
@@ -473,6 +473,19 @@ void _yr_compiler_pop_file_name(
 }
 
 
+int _yr_compiler_get_var_frame(
+    YR_COMPILER* compiler)
+{
+  int i, result = 0;
+
+  for (i = 0; i < compiler->loop_depth; i++)
+     result += compiler->loop[i].vars_count +
+               compiler->loop[i].vars_internal_count;
+
+  return result;
+}
+
+
 YR_API char* yr_compiler_get_current_file_name(
     YR_COMPILER* compiler)
 {
@@ -869,7 +882,7 @@ YR_API int yr_compiler_get_rules(
   return ERROR_SUCCESS;
 }
 
-int _yr_compiler_define_variable(
+static int _yr_compiler_define_variable(
     YR_COMPILER* compiler,
     YR_EXTERNAL_VARIABLE* external)
 {