The current inferrence system walks expressions from "top to bottom".
Starting from definitions higher in the source file, and down. When a
call is encountered, we use the information known for the callee
definition we have at the moment it is inferred.
This causes interesting issues in the case where the callee doesn't
have annotations and in only partially known. For example:
```
pub fn list(fuzzer: Option<a>) -> Option<List<a>> {
inner(fuzzer, [])
}
fn inner(fuzzer, xs) -> Option<List<b>> {
when fuzzer is {
None -> Some(xs)
Some(x) -> Some([x, ..xs])
}
}
```
In this small program, we infer `list` first and run into `inner`.
Yet, the arguments for `inner` are not annotated, so since we haven't
inferred `inner` yet, we will create two unbound variables.
And naturally, we will link the type of `[]` to being of the same type
as `xs` -- which is still unbound at this point. The return type of
`inner` is given by the annotation, so all-in-all, the unification
will work without ever having to commit to a type of `[]`.
It is only later, when `inner` is inferred, that we will generalise
the unbound type of `xs` to a generic which the same as `b` in the
annotation. At this point, `[]` is also typed with this same generic,
which has a different id than `a` in `list` since it comes from
another type definition.
This is unfortunate and will cause issues down the line for the code
generation. The problem doesn't occur when `inner`'s arguments are
properly annotated or, when `inner` is actually inferred first.
Hence, I saw two possible avenues for fixing this problem:
1. Detect the presence of 'uncongruous generics' in definitions after
they've all been inferred, and raise a user error asking for more
annotations.
2. Infer definitions in dependency order, with definitions used in
other inferred first.
This commit does (2) (although it may still be a good idea to do (1)
eventually) since it offers a much better user experience. One way to
do (2) is to construct a dependency graph between function calls, and
ensure perform a topological sort.
Building such graph is, however, quite tricky as it requires walking
through the AST while maintaining scope etc. which is more-or-less
already what the inferrence step is doing; so it feels like double
work.
Thus instead, this commit tries to do a deep-first inferrence and
"pause" inferrence of definitions when encountering a call to fully
infer the callee first. To achieve this properly, we must ensure that
we do not infer the same definition again, so we "remember" already
inferred definitions in the environment now.
We have been a bit too strict on disallowing 'allow_cast' propagations. This is really only problematic for nested elements like Tuple's elements or App's args. However, for linked and unbound var it is probably okay, and it certainly is as well for function arguments.
Also slightly extended the check test 'framework' to allow registering side-dependency and using them from another module. This allows to check the interplay between opaque type from within and outside of their host module.
Discard pattern are _dangerous_ is used recklessly. The problem comes
from maintenance and when adding new fields. We usually don't get any
compiler warnings which may lead to missing spots and confusing
behaviors.
So I have, in some cases, inline discard to explicitly list all
fields. That's a bit more cumbersome to write but hopefully will catch
a few things for us in the future.
Before this commit, we would always show the 'declared form' of type aliases, with their generic, non-instantiated parameters. This now tries to unify the annotation with the underlying inferred type to provide even better alias pretty printing.
The parameter is special as it takes no annotation but a 'via' keyword followed by an expression that should unify to a Fuzzer<a>, where Fuzzer<a> = fn(Seed) -> (Seed, a). The current commit only allow name identifiers for now. Ultimately, this may allow full expressions.
This commit allows Data to be optionally annotated with a
phantom-type. This doesn't change anything in codegen but we can now
leverage this information to generate better blueprint schemas.
This was somewhat weirdly done, with a boolean 'imported' set on the
formers; but an explicit new warning for values. I don't see the point
of distinguishing them so I just merged them all into a single
warning.
I have however preserved the 'UnusedType' and 'UnusedConstructor'
warnings since they were ALSO used for unused private constructors or
types.
I initially removed the 'UnkownTypeConstructor' since it wasn't used anywhere and was in fact dead-code. On second thoughts however, it is nicer to provide a slightly better error message when a constructor is missing as well as some valid suggestion. Prior to that commit, we would simply return a 'UnknownVariable' and the hint might suggest lowercase identifiers; which is wrong.
It is now possible to leave a hole in a type annotation and have the compiler fill-in the expected type of us.
This is a pretty useful debugging tool when playing with complex functions.
Before that commit, the type-checker would allow unsafe list patterns
such as:
```
let [x] = xs
when xs is {
[x] -> ...
[x, ..] -> ...
}
```
This is quite unsafe and can lead to confusing situations. Now at
least the compiler warns about this. It isn't perfect though,
especially in the presence of clause guards. But that's a start.
I decided to invert how I'm doing it. I'm passing
in a new argument to unify in environment called
allow_cast: bool and essentially at various
unification sites I can control whether or not I
want to allow casting to even occur. So we can
assume it's false by default always and then we
turn it on in a few places vs. just opening the
flood gates and locking it down at various sites
as they come up# Please enter the commit message
for your changes. Lines starting
* you cannot cast FROM Data with a `let`
* you cannot cast FROM Data by passing
Data to none Data when calling a function
* you MUST use `assert` to cast from data
* you can cast INTO Data with a `let`
* you can cast INTO Data by passing none Data
to Data when calling a function
* You cannot assert cast Data without an
annotation
KtorZ