This patch functorises the generic expression printer, in order to be able to
re-use it for end-user printing.
It makes it possible to have an end-user, localised printer that shares the code
for e.g. priority and automatic parens handling.
A generic AST rewriting that disambiguates variables (very simple to write with
bindlib) is also added and used in the OCaml backend for something safer than
just appending `_user` (-- this also handles clashing variables that could be
introduced during compilation which would have generated wrong code before this)
Finally, the `explain` plugin is adapted to use the new printer.
Ah, and `String.format_t` was tweaked to correctly print strings that might
contain unicode without breaking alignment, and should be used instead of
`format_string` or `%s` whenever unicode can be expected.
This uses the same disambiguation mechanism put in place for
structures, calling the typer on individual rules on the desugared AST
to propagate types, in order to resolve ambiguous operators like `+`
to their strongly typed counterparts (`+!`, `+.`, `+$`, `+@`, `+$`) in
the translation to scopelang.
The patch includes some normalisation of the definition of all the
operators, and classifies them based on their typing policy instead of
their arity. It also adds a little more flexibility:
- a couple new operators, like `-` on date and duration
- optional type annotation on some aggregation constructions
The `Shared_ast` lib is also lightly restructured, with the `Expr`
module split into `Type`, `Operator` and `Expr`.
