[m-rev.] for review: term_io.m base ops

[Julien Fischer]

On Mon, 3 Jul 2023, Zoltan Somogyi wrote:

> Move base of term_io.m to X_to_string, write_X, format_X.
> 
> library/term_io.m:
>     Move the base operations of term_io.m to the structure we use
>     in parse_tree_out*.m in the compiler, where for every type X,
>     there is a function X_to_string, and two predicates write_X and format_X,
>     with the former operating on I/O states, and the latter operating on
>     arbitrary streams. The idea is to apply the "don't repeat yourself"
>     principle by having both X_to_string and write_X just call format_X.

...

That's fine.

Julien.