previously, `#eval` would happily evaluate expressions that contain
`sorry`, either explicitly or because of failing tactics. In conjunction
with operations like array access this can lead to the lean process
crashing, which isn't particularly great.
So how `#eval` will refuse to run code that (transitively) depends on
the `sorry` axiom (using the same code as `#print axioms`).
If the user really wants to run it, they can use `#eval!`.
Closes#1697
This PR updates the screenshots and instructions in the quickstart guide
for the most recent Lean 4 VS Code extension version and makes a small
stylistic change suggested by @semorrison.
The `elab_as_elim` elaborator eagerly elaborates arguments that can help
with elaborating the motive, however it does not include the transitive
closure of parameters appearing in types of parameters appearing in ...
types of targets.
This leads to counter-intuitive behavior where arguments supplied to the
eliminator may unexpectedly have postponed elaboration, causing motives
to be type incorrect for under-applied eliminators such as the
following:
```lean
class IsEmpty (α : Sort u) : Prop where
protected false : α → False
@[elab_as_elim]
def isEmptyElim [IsEmpty α] {p : α → Sort _} (a : α) : p a :=
(IsEmpty.false a).elim
example {α : Type _} [IsEmpty α] :
id (α → False) := isEmptyElim (α := α)
```
The issue is that when `isEmptyElim (α := α)` is computing its motive,
the value of the postponed argument `α` is still an unassignable
metavariable. With this PR, this argument is now among those that are
eagerly elaborated since it appears as the type of the target `a`.
This PR also contains some other fixes:
* When underapplied, does unification when instantiating foralls in the
expected type.
* When overapplied, type checks the generalized-and-reverted expected
type.
* When collecting targets, collects them in the correct order.
Adds trace class `trace.Elab.app.elab_as_elim`.
This is a followup to #4722, which added motive type checking but
exposed the eagerness issue.
Also extends existing definition for `getScope`/`getScopes` and
clarifies that the `end` command is optional at the end of a file.
---------
Co-authored-by: Kyle Miller <kmill31415@gmail.com>
The original idea was to use `bif` in computation contexts and `if` in
propositional contexts, but this turned out to be really inconvenient in
practice.
code to create nested `PProd`s, and project out, and related functions
were scattered in variuos places. This unifies them in
`Lean.Meta.PProdN`.
It also consistently avoids the terminal `True` or `PUnit`, for slightly
easier to read constructions.
This refactoring PR changes the structure of the `FunInd` module, with
the main purpose to make it easier to support mutual structural
recursion.
In particular the recursive calls are now longer recognized by their
terms (simple for well-founded recursion, `.app oldIH [arg, proof]`, but
tedious for structural recursion and even more so for mutual structural
recursion), but the type after replacing `oldIH` with `newIH`, where the
type will be simply and plainly `mkAppN motive args`).
We also no longer try to guess whether we deal with well-founded or
structural recursion but instead rely on the `EqnInfo` environment
extensions. The previous code tried to handle both variants, but they
differ too much, so having separate top-level functions is easier.
This also fuses the `foldCalls` and `collectIHs` traversals and
introduces a suitable monad for collecting the inductive hypotheses.
This is part 2 of 2 of #4801 (which closes#4654). That PR was split in
two to allow a stage0 update between declaring the `usize` functions and
using them where they are needed.
Add efficient `usize` functions for `Array`, `ByteArray`, `FloatArray`.
This is part 1 of 2 since there is a need to update stage0 between the
two parts. (See discussion below.)
Closes#4654
Changes:
- We avoid the thread local storage.
- We use a hash map to ensure that cached values are not lost.
- We remove `check_system`. If this becomes an issue in the future we
should precompute the remaining amount of stack space, and use a cheaper
check.
- We add a `Expr.replaceImpl`, and will use it to implement
`Expr.replace` after update-stage0
Declarations with `@[elab_as_elim]` could elaborate as type-incorrect
expressions. Reported by Jireh Loreaux [on
Zulip](https://leanprover.zulipchat.com/#narrow/stream/287929-mathlib4/topic/bug.20in.20revert/near/450522157).
(In principle the elabAsElim routine could revert fvars appearing in the
expected type that depend on the discriminants (if the discriminants are
fvars) to increase the likelihood of type correctness, but that's at the
cost of some complexity to both the elaborator and to the user.)
Now it suggests using `@[ext (iff := false)]` to disable generating the
`ext_iff` lemma.
This PR also adjusts error messages and attribute documentation.
Additionally, to simplify the code now the `x` and `y` arguments can't
come in reverse order (this feature was was added in the refactor
#4543).
Closes#4758
