This page is part of the web mail archives of SRFI 105 from before July 7th, 2015. The new archives for SRFI 105 contain all messages, not just those from before July 7th, 2015.
Here's my thought. Suggesting #!srfi-105 marker doesn't mean you should mark every file that uses srfi-105 with the marker. Some implementations may support srfi-105 by default, and interpret {} as curly-infix notation without the marker. If you *know* you use such implementations then you don't need to bother to mark up your code by #!srfi-105 at all. However, some other implementations may need to switch interpretation of {} file-by-file basis. Such implementation would add its own extension to the switch. Gauche will for sure, and for the backward compatibility, srfi-105 mode won't be the default, at least for a while (because I know some production code relies on the current interpretation of {} in Gauche). So, isn't it better that such implementations use the same marker, instead of having different markers? Then, if you wish your code to be extremely portable out-of-box, you add #!srfi-105 marker for extra safety. Of course, you can still distribute your code without the marker and just say "my code using srfi-105, please turn on the extension if you run it on an implementation that doesn't support it by default." If srfi-105 doesn't suggest the marker at all, the latter would be the only choice. I think it is better to have another option.