Do keep in mind portable here is with regards to "between implementations" and not "per platform." Code between PyPy and CPython isn't guaranteed to be 100% por

Do keep in mind portable here is with regards to "between implementations" and not "per platform." Code between PyPy and CPython isn't guaranteed to be 100% portable (although they try), and in Scheme it's much the same way. And you shouldn't think in terms of C, C++, etc being portable. There's lots of code written for GCC that doesn't conform to an explicit C++ standard (C++11/14 try to change this, but still). In the same way, you're really writing to the standard of language your C/C++ compiler implements. It's hairy, but the fact that things are not portable is just given more visibility in Scheme. Reasons for this are probably varied, but it also has to do with the variation in how Schemes are implemented at the lowest level (think Guile vs. CHICKEN, just in terms of GC they're worlds apart). At the end of the day, some code can be written to be portable (see some SRFIs) but we usually don't worry about minor inconsistencies within the larger Scheme community.