Improve parsing even further #153
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This permits `use foo::grammar::*`
The old code was kind of specific to `$ . F` where `.` is a mode. This is going to allow us to accommodate new modes more easily.
We now support optional lists.
We are going to want to make recursive modes.
this will better support the new gated parsing mode
We don't need this anymore.
This will make it easier to support fixed point parsing.
This helps resolve some annoying ambiguities while keeping the ones I think we want.
and add a test
It is sometimes useful to see EXACTLY what is going on
behavior is still broken
We are going to rework the way that variables are given precedence to use explicit rejection instead.
When one variant is tagged as `#[variable]`, we now automatically reject variable names from other variants. This means we can use `#[precedence]` just to encode true *precedence* (i.e., of operators). This was important since there was a conflict where variables wanted to be the same *precedence* as other identifiers in a logical sense.
We are going to need access to it when we recurse. Besides, the code looks cleaner this way!
This makes us panic safe, but it also just reads much more nicely.
Are we in Left position, right position, etc. (see docs) This will be used to guide parsing of variants so that we can properly handle recursion.
We used to also consider precedence, but we are moving away from that approach. Remove some tests that no longer test a relevant edge case.
We are going to start enforcing the invariant that an expression
with priority N can only directly things of higher priority.
In that case for something like this:
```
enum Expr {
Id(Id),
Literal(Literal),
#[precedence(1, left)]
Add(Expr, Expr),
#[precedence(2, left)]
Mul(Expr, Expr),
}
```
you want Id/Literal to be max priority so they can be embedded
into anything.
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@bors r+ |
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I guess we didn't enable bors yet. :) |
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Parsing now supports:
Foo<>struct Foo where [] {but can just writestruct Foo {Expr = Expr + Exprand things like that.also adds a custom testing framework (
parser-torture-tests) as well as an example language (formality-eg). The formality language is incomplete.