getchar does take a continuation of sorts (as in continuation passing) which is passed the input. In one my initial drafts, getchar was a special form that would accept input at the point of evaluation, which was really funny and unpredictable.
putchar I feel kind of weird about, it acting as an identity function with a side effect is kind of weird; I'm not sure changing it to take a second argument as a continuation would make it better or worse.
Regarding the de Bruijn indices, I don't think there's a huge distinction between writing 3 vs writing ---: it would still form a single lexical token, so I feel like --- is just more noise.
Perhaps a de Bruijn index register you could move around and dereference? e.g. from index 1, index 3 is >>*, then index 2 from there is <*. But that feels less functional, because you're now imperatively manipulating some hidden state.
putchar I feel kind of weird about, it acting as an identity function with a side effect is kind of weird; I'm not sure changing it to take a second argument as a continuation would make it better or worse.
Regarding the de Bruijn indices, I don't think there's a huge distinction between writing 3 vs writing ---: it would still form a single lexical token, so I feel like --- is just more noise.
Perhaps a de Bruijn index register you could move around and dereference? e.g. from index 1, index 3 is >>*, then index 2 from there is <*. But that feels less functional, because you're now imperatively manipulating some hidden state.