"Any plans to generalize 'call-w/stdout and 'call-w/stdin to 'parameterize?"
As a side note to this, I think it would be very preferable to have a `parameterize` form which `call-w/stdin` and `call-w/stdout` would call. It should behave similarly to Racket's parameterize.
This isn't necessary for an implementation of Arc 3.1, but it's very useful in practice: you could provide a way for users to create their own parameters and then call parameterize on them. This is what ar and Nu do, and it's incredibly convenient, especially when you provide a way to make the parameters implicit.
It really does depend on your goals, though. Do you intend for this to be just an implementation of Arc 3.1 and nothing more? Or do you intend to provide convenient features that Arc 3.1 doesn't have? Your work on numerical functions seems to suggest that you're not entirely against extending your Arc runtime to do things that Arc 3.1 doesn't.
* : By "implicit parameters" I mean parameters that you don't have to call to extract their value. In other words, you can just say `stdin` rather than `(stdin)` for instance.