Two interdependent changes here:
1. Enforce all instances of Shared_ast.gexpr to use the generic type for marks.
This makes the interfaces a tad simpler to manipulate: you now write
`('a, 'm) gexpr` rather than `('a, 'm mark) gexpr`.
2. Define a polymorphic `Custom` mark case for use by pass-specific annotations.
And leverage this in the typing module
The module is renamed to `Mark`, and functions renamed to avoid redundancy:
`Marked.mark` is now `Mark.add`
`Marked.unmark` is now `Mark.remove`
`Marked.map_under_mark` is now simply `Mark.map`
etc.
`Marked.same_mark_as` is replaced by `Mark.copy`, but with the arguments
swapped (which seemed more convenient throughout)
Since a type `Mark.t` would indicate a mark, and to avoid confusion, the type
`Marked.t` is renamed to `Mark.ed` as a shorthand for `Mark.marked` ; this part
can easily be removed if that's too much quirkiness.
- Fix the printer for scopes
- Improve the printer for struct types
- Remove `Print.expr'`. Use `Expr.format` as the function with simplified arguments instead.
- `Print.expr` no longer needs the context
- This removes the need for `expr ~debug` + `expr_debug` ;
use `Print.expr` for normal (non-debug) output,
and `Print.expr' ?debug ()` for possibly debug output.
- This improves consistency of debug expr output in many places
- Prints simplified operators (without type suffix) in non-verbose mode
(this patch also fixes some cases of `Expr.skip_wrappers` and leverages the
binder equality provided by Bindlib)
The phantom polymorphic variant qualifying AST nodes is reversed:
- previously, we were explicitely restricting each AST node to the passes where it belonged using a closed type (e.g. `[< dcalc | lcalc]`)
- now, each node instead declares the "feature" it provides using an open type (e.g. `[> 'Exceptions ]`)
- then the AST for a specific pass limits the features it allows with a closed type
The result is that you can mix and match all features if you wish,
even if the result is not a valid AST for any given pass. More
interestingly, it's now easier to write a function that works on
different ASTs at once (it's the inferred default if you don't write a
type restriction).
The opportunity was also taken to simplify the encoding of the
operators, which don't need a second type parameter anymore.
Interstingly enough, it was already implemented in the Python backend.
Required to implement *pro rata temporis*, which the US tax section 121 does
make use of.
Only allowed for durations expressed in days (as returned by `<date> - <date>`),
of course.
