[dleslie]

They're fairly strict; if you code to RnRS and use only SRFIs then you'll find your code to be fairly portable... And nigh-useless.

The problem with the Scheme standards is that the committee refuses to be opinionated about implementation details, and so the standard is defined in terms of itself with little to no consideration for the environment in which Scheme will operate. In practical terms, this means that if you want to communicate with other libraries, or virtually any aspect of the system on which you're running, then you're venturing outside of the Scheme specification and into implementation-specific territory.

Scheme is a toy language. The implementations are not, but then they aren't Scheme so much as they are Scheme with useful extensions.

[kovrik]

I don't know, every time I check different common implementations (Racket, Guile, Chicken, Chez, Kawa) - they all act very different. Very often even a very simple code snippet works fine in one implementation, but not in the other(s).

And while writing my own Scheme, I literally had to choose "Ok, I will implement this Racket-way; This I will implement Guile-way" etc.

[Johnny_Brahms]

I have found that you fairly easily can write portable r6rs code, but whenever you step outside r6rs (for stuff that isn't standard, like networking) it becomes an exhibition of cond-expand abuse.