Sorry for asking obtuse questions obtusely. Let me try this way:
How much would codetree need to change to accept a function or macro as input instead of a file, and produce output that is similarly meaningful? (Not at all, a little bit, a lot).
Sorry again for poor question quality, and to harp on what increasingly appears to be an unimportant point.
I assume by taking a fn as input you mean taking a fn whose return values would become the input. That would not be hard, but the clean way to do it would be to modify read so that it could take a fn as an argument.
