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.
Changelog:
---
A lot has been going on, with more than 530 patches and 70 PRs merged since
0.7.0 last summer. In summary:
- Quite a lot of syntax improvements and changes. Checkout the latest
[cheat-sheet](https://catalalang.github.io/catala/syntax.pdf) for an overview
- Allow local `let ... equals ... in ...` definitions
- Better error messages and positions throughout
- Added the ability to directly call a scope and retrieve its outputs, like a
function
- Added disambiguation, allowing to access structure fields without specifying
the structure type each time
- Added automated resolution of operators, allowing e.g. to write just `+` in
place of all the type-specific operators `+.`, `+$`, `+@`, `+^`, etc.
- More consistent priority for operators. It is no longer allowed to write `a
and b or c` without parenthesis.
- Added and changed some operators (`date + duration` now allowed either way,
`int / int` now returns a decimal, added `duration / duration`)
- Added the ability to have variables and functions defined at
top-level (outside of any scope). See annex A of the tutorial for details.
- Added support for functions with multiple arguments
- Some big refactors in the compiler, allowing much better code sharing between
the different passes, and making it much easier to extend. Also added the
possibility to run the type-checker earlier, etc.
- Countless bug-fixes
- Improvements to our proof backend with Z3
- A tool to automatically synchronise with the upstream French law from
Legifrance
