We intend to provide regular "minor version" releases of the Lean language at approximately monthly intervals. There is not yet a strong guarantee of backwards compatibility between versions, only an expectation that breaking changes will be documented in this file.
This file contains work-in-progress notes for the upcoming release, as well as previous stable releases. Please check the releases page for the current status of each version.
supportInterpreter := true
on Windows should now be run via lake exe
to function properly.The way Lean is built on Windows has changed (see PR #3601). As a result, Lake now dynamically links executables with supportInterpreter := true
on Windows to libleanshared.dll
and libInit_shared.dll
. Therefore, such executables will not run unless those shared libraries are co-located with the executables or part of PATH
. Running the executable via lake exe
will ensure these libraries are part of PATH
.
In a related change, the signature of the nativeFacets
Lake configuration options has changed from a static Array
to a function (shouldExport : Bool) → Array
. See its docstring or Lake's README for further details on the changed option.
Lean now generates an error if the type of a theorem is not a proposition.
Importing two different files containing proofs of the same theorem is no longer considered an error. This feature is particularly useful for theorems that are automatically generated on demand (e.g., equational theorems).
Functional induction principles.
Derived from the definition of a (possibly mutually) recursive function, a functional induction principle is created that is tailored to proofs about that function.
For example from:
def ackermann : Nat → Nat → Nat
| 0, m => m + 1
| n+1, 0 => ackermann n 1
| n+1, m+1 => ackermann n (ackermann (n + 1) m)
we get
ackermann.induct (motive : Nat → Nat → Prop) (case1 : ∀ (m : Nat), motive 0 m)
(case2 : ∀ (n : Nat), motive n 1 → motive (Nat.succ n) 0)
(case3 : ∀ (n m : Nat), motive (n + 1) m → motive n (ackermann (n + 1) m) → motive (Nat.succ n) (Nat.succ m))
(x x : Nat) : motive x x
It can be used in the induction
tactic using the using
syntax:
induction n, m using ackermann.induct
The termination checker now recognizes more recursion patterns without an
explicit termination_by
. In particular the idiom of counting up to an upper
bound, as in
def Array.sum (arr : Array Nat) (i acc : Nat) : Nat :=
if _ : i < arr.size then
Array.sum arr (i+1) (acc + arr[i])
else
acc
is recognized without having to say termination_by arr.size - i
.
Shorter instances names. There is a new algorithm for generating names for anonymous instances. Across Std and Mathlib, the median ratio between lengths of new names and of old names is about 72%. With the old algorithm, the longest name was 1660 characters, and now the longest name is 202 characters. The new algorithm's 95th percentile name length is 67 characters, versus 278 for the old algorithm. While the new algorithm produces names that are 1.2% less unique, it avoids cross-project collisions by adding a module-based suffix when it does not refer to declarations from the same "project" (modules that share the same root). PR #3089.
Attribute @[pp_using_anonymous_constructor]
to make structures pretty print like ⟨x, y, z⟩
rather than {a := x, b := y, c := z}
.
This attribute is applied to Sigma
, PSigma
, PProd
, Subtype
, And
, and Fin
.
Now structure instances pretty print with parent structures' fields inlined.
That is, if B
extends A
, then { toA := { x := 1 }, y := 2 }
now pretty prints as { x := 1, y := 2 }
.
Setting option pp.structureInstances.flatten
to false turns this off.
Option pp.structureProjections
is renamed to pp.fieldNotation
, and there is now a suboption pp.fieldNotation.generalized
to enable pretty printing function applications using generalized field notation (defaults to true).
Field notation can be disabled on a function-by-function basis using the @[pp_nodot]
attribute.
Added options pp.mvars
(default: true) and pp.mvars.withType
(default: false).
When pp.mvars
is false, expression metavariables pretty print as ?_
and universe metavariables pretty print as _
.
When pp.mvars.withType
is true, expression metavariables pretty print with a type ascription.
These can be set when using #guard_msgs
to make tests not depend on the particular names of metavariables.
#3798 and
#3978.
Hovers for terms in match
expressions in the Infoview now reliably show the correct term.
Added @[induction_eliminator]
and @[cases_eliminator]
attributes to be able to define custom eliminators
for the induction
and cases
tactics, replacing the @[eliminator]
attribute.
Gives custom eliminators for Nat
so that induction
and cases
put goal states into terms of 0
and n + 1
rather than Nat.zero
and Nat.succ n
.
Added option tactic.customEliminators
to control whether to use custom eliminators.
Added a hack for rcases
/rintro
/obtain
to use the custom eliminator for Nat
.
#3629,
#3655, and
#3747.
The #guard_msgs
command now has options to change whitespace normalization and sensitivity to message ordering.
For example, #guard_msgs (whitespace := lax) in cmd
collapses whitespace before checking messages,
and #guard_msgs (ordering := sorted) in cmd
sorts the messages in lexicographic order before checking.
PR #3883.
The #guard_msgs
command now supports showing a diff between the expected and actual outputs. This feature is currently
disabled by default, but can be enabled with set_option guard_msgs.diff true
. Depending on user feedback, this option
may default to true
in a future version of Lean.
Breaking changes:
.eq_<idx>
instead of ._eq_<idx>
, and .def
instead of ._unfold
. Example:
```
def fact : Nat → Nat
| 0 => 1
| n+1 => (n+1) * fact ntheorem ex : fact 0 = 1 := by unfold fact; decide
#check fact.eq_1 -- fact.eq_1 : fact 0 = 1
#check fact.eq_2 -- fact.eq_2 (n : Nat) : fact (Nat.succ n) = (n + 1) * fact n
#check fact.def /- fact.def : ∀ (x : Nat),
fact x =
match x with
| 0 => 1
| Nat.succ n => (n + 1) * fact n
-/
* The coercion from `String` to `Name` was removed. Previously, it was `Name.mkSimple`, which does not separate strings at dots, but experience showed that this is not always the desired coercion. For the previous behavior, manually insert a call to `Name.mkSimple`.
* The `Subarray` fields `as`, `h₁` and `h₂` have been renamed to `array`, `start_le_stop`, and `stop_le_array_size`, respectively. This more closely follows standard Lean conventions. Deprecated aliases for the field projections were added; these will be removed in a future release.
* The change to the instance name algorithm (described above) can break projects that made use of the auto-generated names.
* `Option.toMonad` has been renamed to `Option.getM` and the unneeded `[Monad m]` instance argument has been removed.
v4.7.0
---------
* `simp` and `rw` now use instance arguments found by unification,
rather than always resynthesizing. For backwards compatibility, the original behaviour is
available via `set_option tactic.skipAssignedInstances false`.
[#3507](https://github.com/leanprover/lean4/pull/3507) and
[#3509](https://github.com/leanprover/lean4/pull/3509).
* When the `pp.proofs` is false, now omitted proofs use `⋯` rather than `_`,
which gives a more helpful error message when copied from the Infoview.
The `pp.proofs.threshold` option lets small proofs always be pretty printed.
[#3241](https://github.com/leanprover/lean4/pull/3241).
* `pp.proofs.withType` is now set to false by default to reduce noise in the info view.
* The pretty printer for applications now handles the case of over-application itself when applying app unexpanders.
In particular, the ``| `($_ $a $b $xs*) => `(($a + $b) $xs*)`` case of an `app_unexpander` is no longer necessary.
[#3495](https://github.com/leanprover/lean4/pull/3495).
* New `simp` (and `dsimp`) configuration option: `zetaDelta`. It is `false` by default.
The `zeta` option is still `true` by default, but their meaning has changed.
- When `zeta := true`, `simp` and `dsimp` reduce terms of the form
`let x := val; e[x]` into `e[val]`.
- When `zetaDelta := true`, `simp` and `dsimp` will expand let-variables in
the context. For example, suppose the context contains `x := val`. Then,
any occurrence of `x` is replaced with `val`.
See [issue #2682](https://github.com/leanprover/lean4/pull/2682) for additional details. Here are some examples:
example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
intro x
simp
/-
New goal:
h : z = 9; x := 5 |- x + 4 = z
-/
rw [h]
example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
intro x
-- Using both `zeta` and `zetaDelta`.
simp (config := { zetaDelta := true })
/-
New goal:
h : z = 9; x := 5 |- 9 = z
-/
rw [h]
example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
intro x
simp [x] -- asks `simp` to unfold `x`
/-
New goal:
h : z = 9; x := 5 |- 9 = z
-/
rw [h]
example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
intro x
simp (config := { zetaDelta := true, zeta := false })
/-
New goal:
h : z = 9; x := 5 |- let y := 4; 5 + y = z
-/
rw [h]
* When adding new local theorems to `simp`, the system assumes that the function application arguments
have been annotated with `no_index`. This modification, which addresses [issue #2670](https://github.com/leanprover/lean4/issues/2670),
restores the Lean 3 behavior that users expect. With this modification, the following examples are now operational:
example {α β : Type} {f : α × β → β → β} (h : ∀ p : α × β, f p p.2 = p.2)
(a : α) (b : β) : f (a, b) b = b := by
simp [h]
example {α β : Type} {f : α × β → β → β}
(a : α) (b : β) (h : f (a,b) (a,b).2 = (a,b).2) : f (a, b) b = b := by
simp [h]
In both cases, `h` is applicable because `simp` does not index f-arguments anymore when adding `h` to the `simp`-set.
It's important to note, however, that global theorems continue to be indexed in the usual manner.
* Improved the error messages produced by the `decide` tactic. [#3422](https://github.com/leanprover/lean4/pull/3422)
* Improved auto-completion performance. [#3460](https://github.com/leanprover/lean4/pull/3460)
* Improved initial language server startup performance. [#3552](https://github.com/leanprover/lean4/pull/3552)
* Changed call hierarchy to sort entries and strip private header from names displayed in the call hierarchy. [#3482](https://github.com/leanprover/lean4/pull/3482)
* There is now a low-level error recovery combinator in the parsing framework, primarily intended for DSLs. [#3413](https://github.com/leanprover/lean4/pull/3413)
* You can now write `termination_by?` after a declaration to see the automatically inferred
termination argument, and turn it into a `termination_by …` clause using the “Try this” widget or a code action. [#3514](https://github.com/leanprover/lean4/pull/3514)
* A large fraction of `Std` has been moved into the Lean repository.
This was motivated by:
1. Making universally useful tactics such as `ext`, `by_cases`, `change at`,
`norm_cast`, `rcases`, `simpa`, `simp?`, `omega`, and `exact?`
available to all users of Lean, without imports.
2. Minimizing the syntactic changes between plain Lean and Lean with `import Std`.
3. Simplifying the development process for the basic data types
`Nat`, `Int`, `Fin` (and variants such as `UInt64`), `List`, `Array`,
and `BitVec` as we begin making the APIs and simp normal forms for these types
more complete and consistent.
4. Laying the groundwork for the Std roadmap, as a library focused on
essential datatypes not provided by the core langauge (e.g. `RBMap`)
and utilities such as basic IO.
While we have achieved most of our initial aims in `v4.7.0-rc1`,
some upstreaming will continue over the coming months.
* The `/` and `%` notations in `Int` now use `Int.ediv` and `Int.emod`
(i.e. the rounding conventions have changed).
Previously `Std` overrode these notations, so this is no change for users of `Std`.
There is now kernel support for these functions.
[#3376](https://github.com/leanprover/lean4/pull/3376).
* `omega`, our integer linear arithmetic tactic, is now availabe in the core langauge.
* It is supplemented by a preprocessing tactic `bv_omega` which can solve goals about `BitVec`
which naturally translate into linear arithmetic problems.
[#3435](https://github.com/leanprover/lean4/pull/3435).
* `omega` now has support for `Fin` [#3427](https://github.com/leanprover/lean4/pull/3427),
the `<<<` operator [#3433](https://github.com/leanprover/lean4/pull/3433).
* During the port `omega` was modified to no longer identify atoms up to definitional equality
(so in particular it can no longer prove `id x ≤ x`). [#3525](https://github.com/leanprover/lean4/pull/3525).
This may cause some regressions.
We plan to provide a general purpose preprocessing tactic later, or an `omega!` mode.
* `omega` is now invoked in Lean's automation for termination proofs
[#3503](https://github.com/leanprover/lean4/pull/3503) as well as in
array indexing proofs [#3515](https://github.com/leanprover/lean4/pull/3515).
This automation will be substantially revised in the medium term,
and while `omega` does help automate some proofs, we plan to make this much more robust.
* The library search tactics `exact?` and `apply?` that were originally in
Mathlib are now available in Lean itself. These use the implementation using
lazy discrimination trees from `Std`, and thus do not require a disk cache but
have a slightly longer startup time. The order used for selection lemmas has
changed as well to favor goals purely based on how many terms in the head
pattern match the current goal.
* The `solve_by_elim` tactic has been ported from `Std` to Lean so that library
search can use it.
* New `#check_tactic` and `#check_simp` commands have been added. These are
useful for checking tactics (particularly `simp`) behave as expected in test
suites.
* Previously, app unexpanders would only be applied to entire applications. However, some notations produce
functions, and these functions can be given additional arguments. The solution so far has been to write app unexpanders so that they can take an arbitrary number of additional arguments. However this leads to misleading hover information in the Infoview. For example, while `HAdd.hAdd f g 1` pretty prints as `(f + g) 1`, hovering over `f + g` shows `f`. There is no way to fix the situation from within an app unexpander; the expression position for `HAdd.hAdd f g` is absent, and app unexpanders cannot register TermInfo.
This commit changes the app delaborator to try running app unexpanders on every prefix of an application, from longest to shortest prefix. For efficiency, it is careful to only try this when app delaborators do in fact exist for the head constant, and it also ensures arguments are only delaborated once. Then, in `(f + g) 1`, the `f + g` gets TermInfo registered for that subexpression, making it properly hoverable.
[#3375](https://github.com/leanprover/lean4/pull/3375)
Breaking changes:
* `Lean.withTraceNode` and variants got a stronger `MonadAlwaysExcept` assumption to
fix trace trees not being built on elaboration runtime exceptions. Instances for most elaboration
monads built on `EIO Exception` should be synthesized automatically.
* The `match ... with.` and `fun.` notations previously in Std have been replaced by
`nomatch ...` and `nofun`. [#3279](https://github.com/leanprover/lean4/pull/3279) and [#3286](https://github.com/leanprover/lean4/pull/3286)
Other improvements:
* several bug fixes for `simp`:
* we should not crash when `simp` loops [#3269](https://github.com/leanprover/lean4/pull/3269)
* `simp` gets stuck on `autoParam` [#3315](https://github.com/leanprover/lean4/pull/3315)
* `simp` fails when custom discharger makes no progress [#3317](https://github.com/leanprover/lean4/pull/3317)
* `simp` fails to discharge `autoParam` premises even when it can reduce them to `True` [#3314](https://github.com/leanprover/lean4/pull/3314)
* `simp?` suggests generated equations lemma names, fixes [#3547](https://github.com/leanprover/lean4/pull/3547) [#3573](https://github.com/leanprover/lean4/pull/3573)
* fixes for `match` expressions:
* fix regression with builtin literals [#3521](https://github.com/leanprover/lean4/pull/3521)
* accept `match` when patterns cover all cases of a `BitVec` finite type [#3538](https://github.com/leanprover/lean4/pull/3538)
* fix matching `Int` literals [#3504](https://github.com/leanprover/lean4/pull/3504)
* patterns containing int values and constructors [#3496](https://github.com/leanprover/lean4/pull/3496)
* improve `termination_by` error messages [#3255](https://github.com/leanprover/lean4/pull/3255)
* fix `rename_i` in macros, fixes [#3553](https://github.com/leanprover/lean4/pull/3553) [#3581](https://github.com/leanprover/lean4/pull/3581)
* fix excessive resource usage in `generalize`, fixes [#3524](https://github.com/leanprover/lean4/pull/3524) [#3575](https://github.com/leanprover/lean4/pull/3575)
* an equation lemma with autoParam arguments fails to rewrite, fixing [#2243](https://github.com/leanprover/lean4/pull/2243) [#3316](https://github.com/leanprover/lean4/pull/3316)
* `add_decl_doc` should check that declarations are local [#3311](https://github.com/leanprover/lean4/pull/3311)
* instantiate the types of inductives with the right parameters, closing [#3242](https://github.com/leanprover/lean4/pull/3242) [#3246](https://github.com/leanprover/lean4/pull/3246)
* New simprocs for many basic types. [#3407](https://github.com/leanprover/lean4/pull/3407)
Lake fixes:
* Warn on fetch cloud release failure [#3401](https://github.com/leanprover/lean4/pull/3401)
* Cloud release trace & `lake build :release` errors [#3248](https://github.com/leanprover/lean4/pull/3248)
v4.6.1
---------
* Backport of [#3552](https://github.com/leanprover/lean4/pull/3552) fixing a performance regression
in server startup.
v4.6.0
---------
* Add custom simplification procedures (aka `simproc`s) to `simp`. Simprocs can be triggered by the simplifier on a specified term-pattern. Here is an small example:
```lean
import Lean.Meta.Tactic.Simp.BuiltinSimprocs.Nat
def foo (x : Nat) : Nat :=
x + 10
/--
The `simproc` `reduceFoo` is invoked on terms that match the pattern `foo _`.
-/
simproc reduceFoo (foo _) :=
/- A term of type `Expr → SimpM Step -/
fun e => do
/-
The `Step` type has three constructors: `.done`, `.visit`, `.continue`.
* The constructor `.done` instructs `simp` that the result does
not need to be simplied further.
* The constructor `.visit` instructs `simp` to visit the resulting expression.
* The constructor `.continue` instructs `simp` to try other simplification procedures.
All three constructors take a `Result`. The `.continue` contructor may also take `none`.
`Result` has two fields `expr` (the new expression), and `proof?` (an optional proof).
If the new expression is definitionally equal to the input one, then `proof?` can be omitted or set to `none`.
-/
/- `simp` uses matching modulo reducibility. So, we ensure the term is a `foo`-application. -/
unless e.isAppOfArity ``foo 1 do
return .continue
/- `Nat.fromExpr?` tries to convert an expression into a `Nat` value -/
let some n ← Nat.fromExpr? e.appArg!
| return .continue
return .done { expr := Lean.mkNatLit (n+10) }
We disable simprocs support by using the command set_option simprocs false
. This command is particularly useful when porting files to v4.6.0.
Simprocs can be scoped, manually added to simp
commands, and suppressed using -
. They are also supported by simp?
. simp only
does not execute any simproc
. Here are some examples for the simproc
defined above.
example : x + foo 2 = 12 + x := by
set_option simprocs false in
/- This `simp` command does not make progress since `simproc`s are disabled. -/
fail_if_success simp
simp_arith
example : x + foo 2 = 12 + x := by
/- `simp only` must not use the default simproc set. -/
fail_if_success simp only
simp_arith
example : x + foo 2 = 12 + x := by
/-
`simp only` does not use the default simproc set,
but we can provide simprocs as arguments. -/
simp only [reduceFoo]
simp_arith
example : x + foo 2 = 12 + x := by
/- We can use `-` to disable `simproc`s. -/
fail_if_success simp [-reduceFoo]
simp_arith
The command register_simp_attr <id>
now creates a simp
and a simproc
set with the name <id>
. The following command instructs Lean to insert the reduceFoo
simplification procedure into the set my_simp
. If no set is specified, Lean uses the default simp
set.
simproc [my_simp] reduceFoo (foo _) := ...
The syntax of the termination_by
and decreasing_by
termination hints is overhauled:
mutual
block.where
clause, the termination_by
and
decreasing_by
for that function come before the where
. The
functions in the where
clause can have their own termination hints, each
following the corresponding definition.termination_by
clause can only bind “extra parameters”, that are not
already bound by the function header, but are bound in a lambda (:= fun x
y z =>
) or in patterns (| x, n + 1 => …
). These extra parameters used to
be understood as a suffix of the function parameters; now it is a prefix.Migration guide: In simple cases just remove the function name, and any variables already bound at the header.
def foo : Nat → Nat → Nat := …
-termination_by foo a b => a - b
+termination_by a b => a - b
or
def foo : Nat → Nat → Nat := …
-termination_by _ a b => a - b
+termination_by a b => a - b
If the parameters are bound in the function header (before the :
), remove them as well:
def foo (a b : Nat) : Nat := …
-termination_by foo a b => a - b
+termination_by a - b
Else, if there are multiple extra parameters, make sure to refer to the right ones; the bound variables are interpreted from left to right, no longer from right to left:
def foo : Nat → Nat → Nat → Nat
| a, b, c => …
-termination_by foo b c => b
+termination_by a b => b
In the case of a mutual
block, place the termination arguments (without the
function name) next to the function definition:
-mutual
-def foo : Nat → Nat → Nat := …
-def bar : Nat → Nat := …
-end
-termination_by
- foo a b => a - b
- bar a => a
+mutual
+def foo : Nat → Nat → Nat := …
+termination_by a b => a - b
+def bar : Nat → Nat := …
+termination_by a => a
+end
Similarly, if you have (mutual) recursion through where
or let rec
, the
termination hints are now placed directly after the function they apply to:
-def foo (a b : Nat) : Nat := …
- where bar (x : Nat) : Nat := …
-termination_by
- foo a b => a - b
- bar x => x
+def foo (a b : Nat) : Nat := …
+termination_by a - b
+ where
+ bar (x : Nat) : Nat := …
+ termination_by x
-def foo (a b : Nat) : Nat :=
- let rec bar (x : Nat) : Nat := …
- …
-termination_by
- foo a b => a - b
- bar x => x
+def foo (a b : Nat) : Nat :=
+ let rec bar (x : Nat) : Nat := …
+ termination_by x
+ …
+termination_by a - b
In cases where a single decreasing_by
clause applied to multiple mutually
recursive functions before, the tactic now has to be duplicated.
decreasing_by
changed; the tactic is applied to all
termination proof goals together, not individually.This helps when writing termination proofs interactively, as one can focus
each subgoal individually, for example using ·
. Previously, the given
tactic script had to work for all goals, and one had to resort to tactic
combinators like first
:
def foo (n : Nat) := … foo e1 … foo e2 …
-decreasing_by
-simp_wf
-first | apply something_about_e1; …
- | apply something_about_e2; …
+decreasing_by
+all_goals simp_wf
+· apply something_about_e1; …
+· apply something_about_e2; …
To obtain the old behaviour of applying a tactic to each goal individually,
use all_goals
:
def foo (n : Nat) := …
-decreasing_by some_tactic
+decreasing_by all_goals some_tactic
In the case of mutual recursion each decreasing_by
now applies to just its
function. If some functions in a recursive group do not have their own
decreasing_by
, the default decreasing_tactic
is used. If the same tactic
ought to be applied to multiple functions, the decreasing_by
clause has to
be repeated at each of these functions.
Modify InfoTree.context
to facilitate augmenting it with partial contexts while elaborating a command. This breaks backwards compatibility with all downstream projects that traverse the InfoTree
manually instead of going through the functions in InfoUtils.lean
, as well as those manually creating and saving InfoTree
s. See PR #3159 for how to migrate your code.
Add language server support for call hierarchy requests (PR #3082). The change to the .ilean format in this PR means that projects must be fully rebuilt once in order to generate .ilean files with the new format before features like "find references" work correctly again.
Structure instances with multiple sources (for example {a, b, c with x := 0}
) now have their fields filled from these sources
in strict left-to-right order. Furthermore, the structure instance elaborator now aggressively use sources to fill in subobject
fields, which prevents unnecessary eta expansion of the sources,
and hence greatly reduces the reliance on costly structure eta reduction. This has a large impact on mathlib,
reducing total CPU instructions by 3% and enabling impactful refactors like leanprover-community/mathlib4#8386
which reduces the build time by almost 20%.
See PR #2478 and RFC #2451.
Add pretty printer settings to omit deeply nested terms (pp.deepTerms false
and pp.deepTerms.threshold
) (PR #3201)
Add pretty printer options pp.numeralTypes
and pp.natLit
.
When pp.numeralTypes
is true, then natural number literals, integer literals, and rational number literals
are pretty printed with type ascriptions, such as (2 : Rat)
, (-2 : Rat)
, and (-2 / 3 : Rat)
.
When pp.natLit
is true, then raw natural number literals are pretty printed as nat_lit 2
.
PR #2933 and RFC #3021.
Lake updates:
Other improvements:
intro
be aware of let_fun
#3115rw
#3121mkCongrArg
calls in proofs generated by simp
#3203induction using
followed by a general term #3188let
#3060, fixing #3065swap!
should return a
, not default
` #3197, fixing #3196BEq
on structure with Prop
-fields #3191, fixing #3140casesOnApp
/matcherApp
#3176, fixing #3175deriving
only deriving the first declaration for some handlers #3058, fixing #3057cases h : ...
#3084Modify the lexical syntax of string literals to have string gaps, which are escape sequences of the form "\" newline whitespace*
.
These have the interpetation of an empty string and allow a string to flow across multiple lines without introducing additional whitespace.
The following is equivalent to "this is a string"
.
"this is \
a string"
Add raw string literal syntax. For example, r"\n"
is equivalent to "\\n"
, with no escape processing.
To include double quote characters in a raw string one can add sufficiently many #
characters before and after
the bounding "
s, as in r#"the "the" is in quotes"#
for "the \"the\" is in quotes"
.
PR #2929 and issue #1422.
The low-level termination_by'
clause is no longer supported.
Migration guide: Use termination_by
instead, e.g.:
-termination_by' measure (fun ⟨i, _⟩ => as.size - i)
+termination_by i _ => as.size - i
If the well-founded relation you want to use is not the one that the
WellFoundedRelation
type class would infer for your termination argument,
you can use WellFounded.wrap
from the std libarary to explicitly give one:
-termination_by' ⟨r, hwf⟩
+termination_by x => hwf.wrap x
Support snippet edits in LSP TextEdit
s. See Lean.Lsp.SnippetString
for more details.
Deprecations and changes in the widget API.
Widget.UserWidgetDefinition
is deprecated in favour of Widget.Module
. The annotation @[widget]
is deprecated in favour of @[widget_module]
. To migrate a definition of type UserWidgetDefinition
, remove the name
field and replace the type with Widget.Module
. Removing the name
results in a title bar no longer being drawn above your panel widget. To add it back, draw it as part of the component using <details open=true><summary class='mv2 pointer'>{name}</summary>{rest_of_widget}</details>
. See an example migration here.show_panel_widgets
allows displaying always-on and locally-on panel widgets.RpcEncodable
widget props can now be stored in the infotree.If no usable lexicographic order can be found automatically for a termination proof, explain why. See feat: GuessLex: if no measure is found, explain why.
Option to print inferred termination argument.
With set_option showInferredTerminationBy true
you will get messages like
Inferred termination argument:
termination_by
ackermann n m => (sizeOf n, sizeOf m)
for automatically generated termination_by
clauses.
More detailed error messages for invalid mutual blocks.
Multiple improvements to the output of simp?
and simp_all?
.
Tactics with withLocation *
no longer fail if they close the main goal.
Implementation of a test_extern
command for writing tests for @[extern]
and @[implemented_by]
functions.
Usage is
```
import Lean.Util.TestExtern
test_extern Nat.add 17 37
The head symbol must be the constant with the `@[extern]` or `@[implemented_by]` attribute. The return type must have a `DecidableEq` instance.
Bug fixes for
[#2853](https://github.com/leanprover/lean4/issues/2853), [#2953](https://github.com/leanprover/lean4/issues/2953), [#2966](https://github.com/leanprover/lean4/issues/2966),
[#2971](https://github.com/leanprover/lean4/issues/2971), [#2990](https://github.com/leanprover/lean4/issues/2990), [#3094](https://github.com/leanprover/lean4/issues/3094).
Bug fix for [eager evaluation of default value](https://github.com/leanprover/lean4/pull/3043) in `Option.getD`.
Avoid [panic in `leanPosToLspPos`](https://github.com/leanprover/lean4/pull/3071) when file source is unavailable.
Improve [short-circuiting behavior](https://github.com/leanprover/lean4/pull/2972) for `List.all` and `List.any`.
Several Lake bug fixes: [#3036](https://github.com/leanprover/lean4/issues/3036), [#3064](https://github.com/leanprover/lean4/issues/3064), [#3069](https://github.com/leanprover/lean4/issues/3069).
v4.4.0
---------
* Lake and the language server now support per-package server options using the `moreServerOptions` config field, as well as options that apply to both the language server and `lean` using the `leanOptions` config field. Setting either of these fields instead of `moreServerArgs` ensures that viewing files from a dependency uses the options for that dependency. Additionally, `moreServerArgs` is being deprecated in favor of the `moreGlobalServerArgs` field. See PR [#2858](https://github.com/leanprover/lean4/pull/2858).
A Lakefile with the following deprecated package declaration:
```lean
def moreServerArgs := #[
"-Dpp.unicode.fun=true"
]
def moreLeanArgs := moreServerArgs
package SomePackage where
moreServerArgs := moreServerArgs
moreLeanArgs := moreLeanArgs
... can be updated to the following package declaration to use per-package options:
package SomePackage where
leanOptions := #[⟨`pp.unicode.fun, true⟩]
pp.beta
` to apply beta reduction when pretty printing.Bug fixes for #2628, #2883, #2810, #2925, and #2914.
Lake:
lake init .
and a bare lake init
and will now use the current directory as the package name. #2890lake new
and lake init
will now produce errors on invalid package names such as ..
, foo/bar
, Init
, Lean
, Lake
, and Main
. See issue #2637 and PR #2890.lean_lib
no longer converts its name to upper camel case (e.g., lean_lib bar
will include modules named bar.*
rather than Bar.*
). See issue #2567 and PR #2889.lake new 123-hello
and import «123Hello»
now work correctly). See issue #2865 and PR #2889.lakefile.olean
) to include only those relevant to Lake's workspace loading process. This resolves segmentation faults caused by environment extension type mismatches (e.g., when defining custom elaborators via elab
in configurations). See issue #2632 and PR #2896.math
template has been simplified. See PR #2930.lake exe <target>
now parses target
like a build target (as the help text states it should) rather than as a basic name. For example, lake exe @mathlib/runLinter
should now work. See PR #2932.lake new foo.bar [std]
now generates executables named foo-bar
and lake new foo.bar exe
properly creates foo/bar.lean
. See PR #2932.findModule?
. See PR #2937.simp [f]
does not unfold partial applications of f
anymore. See issue #2042.
To fix proofs affected by this change, use unfold f
or simp (config := { unfoldPartialApp := true }) [f]
.By default, simp
will no longer try to use Decidable instances to rewrite terms. In particular, not all decidable goals will be closed by simp
, and the decide
tactic may be useful in such cases. The decide
simp configuration option can be used to locally restore the old simp
behavior, as in simp (config := {decide := true})
; this includes using Decidable instances to verify side goals such as numeric inequalities.
Many bug fixes:
^
` a right actionDecidable
instances very slow when using cases
tacticsimp
not rewriting in bindersimp
unfolding let
even with zeta := false
optionsimp
(with beta/zeta disabled) and discrimination treesrw ... at h
dsimp
doesn't use rfl
theorems which consist of an unapplied constantdsimp
does not close reflexive equality goals if they are wrapped in metadatarw [h]
uses h
from the environment in preference to h
from the local contextwithAssignableSyntheticOpaque
for assumption
tacticCancel outstanding tasks on document edit in the language server.
Lake:
lake new MyProject math
postUpdate?
configuration option to a post_update
declaration. See the post_update
syntax docstring for more information on the new syntax.:=
syntax for configuration declarations (i.e., package
, lean_lib
, and lean_exe
) has been deprecated. For example, package foo := {...}
is deprecated.LAKE_PKG_URL_MAP
build
), default packages directory (e.g., lake-packages
), and the compiled configuration (e.g., lakefile.olean
) into a new dedicated directory for Lake outputs, .lake
. The cloud release build archives are also stored here, fixing #2713.manifestFile
field of a package configuration.lakefile.olean
compatibility (see #2842 for more details).Environment.mk
and Environment.add
private, and add replay
as a safer alternative.IO.Process.output
no longer inherits the standard input of the caller.match
reduction.DecidableEq
now handles mutual inductive types.postUpdate?
package configuration option. Used by a package to specify some code which should be run after a successful lake update
of the package or one of its downstream dependencies. (lake#185)refine e
now replaces the main goal with metavariables which were created during elaboration of e
and no longer captures pre-existing metavariables that occur in e
(#2502).
withCollectingNewGoalsFrom
, which also affects elabTermWithHoles
, refine'
, calc
(tactic), and specialize
. Likewise, all of these now only include newly-created metavariables in their output.e
were returned inconsistently in different edge cases, causing duplicated goals in the infoview (issue #2495), erroneously closed goals (issue #2434), and unintuitive behavior due to refine e
capturing previously-created goals appearing unexpectedly in e
(no issue; see PR).The error positioning on missing tokens has been improved. In particular, this should make it easier to spot errors in incomplete tactic proofs.
After elaborating a configuration file, Lake will now cache the configuration to a lakefile.olean
. Subsequent runs of Lake will import this OLean instead of elaborating the configuration file. This provides a significant performance improvement (benchmarks indicate that using the OLean cuts Lake's startup time in half), but there are some important details to keep in mind:
lakefile.lean
or lean-toolchain
. You can also force a reconfigure by passing the new --reconfigure
/ -R
option to lake
.-K
) will be fixed at the moment of elaboration. Setting these options when lake
is using the cached configuration will have no effect. To change options, run lake
with -R
/ --reconfigure
.lakefile.olean
is a local configuration and should not be committed to Git. Therefore, existing Lake packages need to add it to their .gitignore
.The signature of Lake.buildO
has changed, args
has been split into weakArgs
and traceArgs
. traceArgs
are included in the input trace and weakArgs
are not. See Lake's FFI example for a demonstration of how to adapt to this change.
The signatures of Lean.importModules
, Lean.Elab.headerToImports
, and Lean.Elab.parseImports
have changed from taking List Import
to Array Import
.
There is now an occs
field
in the configuration object for the rewrite
tactic,
allowing control of which occurrences of a pattern should be rewritten.
This was previously a separate argument for Lean.MVarId.rewrite
,
and this has been removed in favour of an additional field of Rewrite.Config
.
It was not previously accessible from user tactics.
Lean.Meta.getConst?
has been renamed.
We have renamed getConst?
to getUnfoldableConst?
(and getConstNoEx?
to getUnfoldableConstNoEx?
).
These were not intended to be part of the public API, but downstream projects had been using them
(sometimes expecting different behaviour) incorrectly instead of Lean.getConstInfo
.
dsimp
/ simp
/ simp_all
now fail by default if they make no progress.
This can be overridden with the (config := { failIfUnchanged := false })
option.
This change was made to ease manual use of simp
(with complicated goals it can be hard to tell if it was effective)
and to allow easier flow control in tactics internally using simp
.
See the summary discussion
on zulip for more details.
In order to support the failIfUnchanged
configuration option for dsimp
/ simp
/ simp_all
the way simp_all
replaces hypotheses has changed.
In particular it is now more likely to preserve the order of hypotheses.
See simp_all
reorders hypotheses unnecessarily.
(Previously all non-dependent propositional hypotheses were reverted and reintroduced.
Now only such hypotheses which were changed, or which come after a changed hypothesis,
are reverted and reintroduced.
This has the effect of preserving the ordering amongst the non-dependent propositional hypotheses,
but now any dependent or non-propositional hypotheses retain their position amongst the unchanged
non-dependent propositional hypotheses.)
This may affect proofs that use rename_i
, case ... =>
, or next ... =>
.
this
is now a regular identifier again that is implicitly introduced by anonymous have :=
for the remainder of the tactic block. It used to be a keyword that was visible in all scopes and led to unexpected behavior when explicitly used as a binder name.
Make calc
require the sequence of relation/proof-s to have the same indentation,
and add calc
alternative syntax allowing underscores _
in the first relation.
The flexible indentation in calc
was often used to align the relation symbols:
example (x y : Nat) : (x + y) * (x + y) = x * x + y * x + x * y + y * y :=
calc
(x + y) * (x + y) = (x + y) * x + (x + y) * y := by rw [Nat.mul_add]
-- improper indentation
_ = x * x + y * x + (x + y) * y := by rw [Nat.add_mul]
_ = x * x + y * x + (x * y + y * y) := by rw [Nat.add_mul]
_ = x * x + y * x + x * y + y * y := by rw [←Nat.add_assoc]
This is no longer legal. The new syntax puts the first term right after the calc
and each step has the same indentation:
example (x y : Nat) : (x + y) * (x + y) = x * x + y * x + x * y + y * y :=
calc (x + y) * (x + y)
_ = (x + y) * x + (x + y) * y := by rw [Nat.mul_add]
_ = x * x + y * x + (x + y) * y := by rw [Nat.add_mul]
_ = x * x + y * x + (x * y + y * y) := by rw [Nat.add_mul]
_ = x * x + y * x + x * y + y * y := by rw [←Nat.add_assoc]
Update Lake to latest prerelease.
Make go-to-definition on a typeclass projection application go to the instance(s).
Add linter.deprecated
option to silence deprecation warnings.
simp
can track information and can print an equivalent simp only
. PR #1626.
Enforce uniform indentation in tactic blocks / do blocks. See issue #1606.
Moved AssocList
, HashMap
, HashSet
, RBMap
, RBSet
, PersistentArray
, PersistentHashMap
, PersistentHashSet
to the Lean package. The standard library contains versions that will evolve independently to simplify bootstrapping process.
Standard library moved to the std4 GitHub repository.
InteractiveGoals
now has information that a client infoview can use to show what parts of the goal have changed after applying a tactic. PR #1610.
Add [inheritDoc]
attribute. PR #1480.
Expose that panic = default
. PR #1614.
New code generator project has started.
Remove description argument from register_simp_attr
. PR #1566.
Many new doc strings have been added to declarations at Init
.
Update Lake to v4.0.0. See the v4.0.0 release notes for detailed changes.
Mutual declarations in different namespaces are now supported. Example:
mutual
def Foo.boo (x : Nat) :=
match x with
| 0 => 1
| x + 1 => 2*Boo.bla x
def Boo.bla (x : Nat) :=
match x with
| 0 => 2
| x+1 => 3*Foo.boo x
end
A namespace
is automatically created for the common prefix. Example:
mutual
def Tst.Foo.boo (x : Nat) := ...
def Tst.Boo.bla (x : Nat) := ...
end
expands to
namespace Tst
mutual
def Foo.boo (x : Nat) := ...
def Boo.bla (x : Nat) := ...
end
end Tst
Allow users to install their own deriving
handlers for existing type classes.
See example at Simple.lean.
Add tactic congr (num)?
. See doc string for additional details.
match
-syntax notation now checks for unused alternatives. See issue #1371.
Auto-completion for structure instance fields. Example:
example : Nat × Nat := {
f -- HERE
}
fst
now appears in the list of auto-completion suggestions.
Auto-completion for dotted identifier notation. Example:
example : Nat :=
.su -- HERE
succ
now appears in the list of auto-completion suggestions.
nat_lit
is not needed anymore when declaring OfNat
instances. See issues #1389 and #875. Example:
```lean
inductive Bit where
| zero
| one
instance inst0 : OfNat Bit 0 where
ofNat := Bit.zero
instance : OfNat Bit 1 where
ofNat := Bit.one
example : Bit := 0 example : Bit := 1
* Add `[elabAsElim]` attribute (it is called `elab_as_eliminator` in Lean 3). Motivation: simplify the Mathlib port to Lean 4.
* `Trans` type class now accepts relations in `Type u`. See this [Zulip issue](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/Calc.20mode/near/291214574).
* Accept unescaped keywords as inductive constructor names. Escaping can often be avoided at use sites via dot notation.
```lean
inductive MyExpr
| let : ...
def f : MyExpr → MyExpr
| .let ... => .let ...
Throw an error message at parametric local instances such as [Nat -> Decidable p]
. The type class resolution procedure
cannot use this kind of local instance because the parameter does not have a forward dependency.
This check can be disabled using set_option checkBinderAnnotations false
.
Add option pp.showLetValues
. When set to false
, the info view hides the value of let
-variables in a goal.
By default, it is true
when visualizing tactic goals, and false
otherwise.
See issue #1345 for additional details.
Add option warningAsError
. When set to true, warning messages are treated as errors.
Support dotted notation and named arguments in patterns. Example:
def getForallBinderType (e : Expr) : Expr :=
match e with
| .forallE (binderType := type) .. => type
| _ => panic! "forall expected"
"jump-to-definition" now works for function names embedded in the following attributes
@[implementedBy funName]
, @[tactic parserName]
, @[termElab parserName]
, @[commandElab parserName]
,
@[builtinTactic parserName]
, @[builtinTermElab parserName]
, and @[builtinCommandElab parserName]
.
See issue #1350.
Improve MVarId
methods discoverability. See issue #1346.
We still have to add similar methods for FVarId
, LVarId
, Expr
, and other objects.
Many existing methods have been marked as deprecated.
Add attribute [deprecated]
for marking deprecated declarations. Examples:
```lean
def g (x : Nat) := x + 1
-- Whenever f
is used, a warning message is generated suggesting to use g
instead.
@[deprecated g]
def f (x : Nat) := x + 1
#check f 0 -- warning: f
has been deprecated, use g
instead
-- Whenever h
is used, a warning message is generated.
@[deprecated]
def h (x : Nat) := x + 1
#check h 0 -- warning: h
has been deprecated
* Add type `LevelMVarId` (and abbreviation `LMVarId`) for universe level metavariable ids.
Motivation: prevent meta-programmers from mixing up universe and expression metavariable ids.
* Improve `calc` term and tactic. See [issue #1342](https://github.com/leanprover/lean4/issues/1342).
* [Relaxed antiquotation parsing](https://github.com/leanprover/lean4/pull/1272) further reduces the need for explicit `$x:p` antiquotation kind annotations.
* Add support for computed fields in inductives. Example:
```lean
inductive Exp
| var (i : Nat)
| app (a b : Exp)
with
@[computedField] hash : Exp → Nat
| .var i => i
| .app a b => a.hash * b.hash + 1
The result of the Exp.hash
function is then stored as an extra "computed" field in the .var
and .app
constructors;
Exp.hash
accesses this field and thus runs in constant time (even on dag-like values).
a[i]
notation. It is now based on the typeclass
lean
class GetElem (cont : Type u) (idx : Type v) (elem : outParam (Type w)) (dom : outParam (cont → idx → Prop)) where
getElem (xs : cont) (i : idx) (h : dom xs i) : Elem
The notation a[i]
is now defined as follows
lean
macro:max x:term noWs "[" i:term "]" : term => `(getElem $x $i (by get_elem_tactic))
The proof that i
is a valid index is synthesized using the tactic get_elem_tactic
.
For example, the type Array α
has the following instances
lean
instance : GetElem (Array α) Nat α fun xs i => LT.lt i xs.size where ...
instance : GetElem (Array α) USize α fun xs i => LT.lt i.toNat xs.size where ...
You can use the notation a[i]'h
to provide the proof manually.
Two other notations were introduced: a[i]!
and a[i]?
, For a[i]!
, a panic error message is produced at
runtime if i
is not a valid index. a[i]?
has type Option α
, and a[i]?
evaluates to none
if the
index i
is not valid.
The three new notations are defined as follows:
```lean
@[inline] def getElem' GetElem cont idx elem dom (i : idx) (h : dom xs i) : elem :=
getElem xs i h@[inline] def getElem! [GetElem cont idx elem dom] Inhabited elem (i : idx) [Decidable (dom xs i)] : elem :=
if h : _ then getElem xs i h else panic! "index out of bounds"
@[inline] def getElem? GetElem cont idx elem dom (i : idx) [Decidable (dom xs i)] : Option elem :=
if h : _ then some (getElem xs i h) else none
macro:max x:term noWs "[" i:term "]" noWs "?" : term => (getElem? $x $i)
macro:max x:term noWs "[" i:term "]" noWs "!" : term =>
(getElem! $x $i)
macro x:term noWs "[" i:term "]'" h:term:max : term => `(getElem' $x $i $h)
See discussion on [Zulip](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/String.2EgetOp/near/287855425).
Examples:
```lean
example (a : Array Int) (i : Nat) : Int :=
a[i] -- Error: failed to prove index is valid ...
example (a : Array Int) (i : Nat) (h : i < a.size) : Int :=
a[i] -- Ok
example (a : Array Int) (i : Nat) : Int :=
a[i]! -- Ok
example (a : Array Int) (i : Nat) : Option Int :=
a[i]? -- Ok
example (a : Array Int) (h : a.size = 2) : Int :=
a[0]'(by rw [h]; decide) -- Ok
example (a : Array Int) (h : a.size = 2) : Int :=
have : 0 < a.size := by rw [h]; decide
have : 1 < a.size := by rw [h]; decide
a[0] + a[1] -- Ok
example (a : Array Int) (i : USize) (h : i.toNat < a.size) : Int :=
a[i] -- Ok
The get_elem_tactic
is defined as
macro "get_elem_tactic" : tactic =>
`(first
| get_elem_tactic_trivial
| fail "failed to prove index is valid, ..."
)
The get_elem_tactic_trivial
auxiliary tactic can be extended using macro_rules
. By default, it tries trivial
, simp_arith
, and a special case for Fin
. In the future, it will also try linarith
.
You can extend get_elem_tactic_trivial
using my_tactic
as follows
macro_rules
| `(tactic| get_elem_tactic_trivial) => `(tactic| my_tactic)
Note that Idx
's type in GetElem
does not depend on Cont
. So, you cannot write the instance instance : GetElem (Array α) (Fin ??) α fun xs i => ...
, but the Lean library comes equipped with the following auxiliary instance:
instance [GetElem cont Nat elem dom] : GetElem cont (Fin n) elem fun xs i => dom xs i where
getElem xs i h := getElem xs i.1 h
and helper tactic
macro_rules
| `(tactic| get_elem_tactic_trivial) => `(tactic| apply Fin.val_lt_of_le; get_elem_tactic_trivial; done)
Example:
example (a : Array Nat) (i : Fin a.size) :=
a[i] -- Ok
example (a : Array Nat) (h : n ≤ a.size) (i : Fin n) :=
a[i] -- Ok
Better support for qualified names in recursive declarations. The following is now supported:
namespace Nat
def fact : Nat → Nat
| 0 => 1
| n+1 => (n+1) * Nat.fact n
end Nat
Add support for CommandElabM
monad at #eval
. Example:
```lean
import Lean
open Lean Elab Command
#eval do
let id := mkIdent `foo
elabCommand (← `(def $id := 10))
#eval foo -- 10
* Try to elaborate `do` notation even if the expected type is not available. We still delay elaboration when the expected type
is not available. This change is particularly useful when writing examples such as
```lean
#eval do
IO.println "hello"
IO.println "world"
That is, we don't have to use the idiom #eval show IO _ from do ...
anymore.
Note that auto monadic lifting is less effective when the expected type is not available.
Monadic polymorphic functions (e.g., ST.Ref.get
) also require the expected type.
On Linux, panics now print a backtrace by default, which can be disabled by setting the environment variable LEAN_BACKTRACE
to 0
.
Other platforms are TBD.
The group(·)
syntax
combinator is now introduced automatically where necessary, such as when using multiple parsers inside (...)+
.
Add "Typed Macros": syntax trees produced and accepted by syntax antiquotations now remember their syntax kinds, preventing accidental production of ill-formed syntax trees and reducing the need for explicit :kind
antiquotation annotations. See PR for details.
Aliases of protected definitions are protected too. Example: ```lean protected def Nat.double (x : Nat) := 2*x
namespace Ex export Nat (double) -- Add alias Ex.double for Nat.double end Ex
open Ex
#check Ex.double -- Ok
#check double -- Error, Ex.double
is alias for Nat.double
which is protected
* Use `IO.getRandomBytes` to initialize random seed for `IO.rand`. See discussion at [this PR](https://github.com/leanprover/lean4-samples/pull/2).
* Improve dot notation and aliases interaction. See discussion on [Zulip](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/Namespace-based.20overloading.20does.20not.20find.20exports/near/282946185) for additional details.
Example:
```lean
def Set (α : Type) := α → Prop
def Set.union (s₁ s₂ : Set α) : Set α := fun a => s₁ a ∨ s₂ a
def FinSet (n : Nat) := Fin n → Prop
namespace FinSet
export Set (union) -- FinSet.union is now an alias for `Set.union`
end FinSet
example (x y : FinSet 10) : FinSet 10 :=
x.union y -- Works
ext
and enter
conv tactics can now go inside let-declarations. Example:
example (g : Nat → Nat) (y : Nat) (h : let x := y + 1; g (0+x) = x) : g (y + 1) = y + 1 := by
conv at h => enter [x, 1, 1]; rw [Nat.zero_add]
/-
g : Nat → Nat
y : Nat
h : let x := y + 1;
g x = x
⊢ g (y + 1) = y + 1
-/
exact h
Add zeta
conv tactic to expand let-declarations. Example:
example (h : let x := y + 1; 0 + x = y) : False := by
conv at h => zeta; rw [Nat.zero_add]
/-
y : Nat
h : y + 1 = y
⊢ False
-/
simp_arith at h
Improve namespace resolution. See issue #1224. Example:
import Lean
open Lean Parser Elab
open Tactic -- now opens both `Lean.Parser.Tactic` and `Lean.Elab.Tactic`
Rename constant
command to opaque
. See discussion at Zulip.
Extend induction
and cases
syntax: multiple left-hand-sides in a single alternative. This extension is very similar to the one implemented for match
expressions. Examples:
```lean
inductive Foo where
| mk1 (x : Nat) | mk2 (x : Nat) | mk3
def f (v : Foo) :=
match v with
| .mk1 x => x + 1
| .mk2 x => 2*x + 1
| .mk3 => 1
theorem f_gt_zero : f v > 0 := by
cases v with
| mk1 x | mk2 x => simp_arith! -- New feature used here!
| mk3 => decide
* [`let/if` indentation in `do` blocks in now supported.](https://github.com/leanprover/lean4/issues/1120)
* Add unnamed antiquotation `$_` for use in syntax quotation patterns.
* [Add unused variables linter](https://github.com/leanprover/lean4/pull/1159). Feedback welcome!
* Lean now generates an error if the body of a declaration body contains a universe parameter that does not occur in the declaration type, nor is an explicit parameter.
Examples:
```lean
/-
The following declaration now produces an error because `PUnit` is universe polymorphic,
but the universe parameter does not occur in the function type `Nat → Nat`
-/
def f (n : Nat) : Nat :=
let aux (_ : PUnit) : Nat := n + 1
aux ⟨⟩
/-
The following declaration is accepted because the universe parameter was explicitly provided in the
function signature.
-/
def g.{u} (n : Nat) : Nat :=
let aux (_ : PUnit.{u}) : Nat := n + 1
aux ⟨⟩
Add subst_vars
tactic.
Fix autoParam
in structure fields lost in multiple inheritance..
Add [eliminator]
attribute. It allows users to specify default recursor/eliminators for the induction
and cases
tactics.
It is an alternative for the using
notation. Example:
```lean
@[eliminator] protected def recDiag {motive : Nat → Nat → Sort u}
(zero_zero : motive 0 0)
(succ_zero : (x : Nat) → motive x 0 → motive (x + 1) 0)
(zero_succ : (y : Nat) → motive 0 y → motive 0 (y + 1))
(succ_succ : (x y : Nat) → motive x y → motive (x + 1) (y + 1))
(x y : Nat) : motive x y :=
let rec go : (x y : Nat) → motive x y
| 0, 0 => zero_zero
| x+1, 0 => succ_zero x (go x 0)
| 0, y+1 => zero_succ y (go 0 y)
| x+1, y+1 => succ_succ x y (go x y)
go x y
termination_by go x y => (x, y)
def f (x y : Nat) :=
match x, y with
| 0, 0 => 1
| x+1, 0 => f x 0
| 0, y+1 => f 0 y
| x+1, y+1 => f x y
termination_by f x y => (x, y)
example (x y : Nat) : f x y > 0 := by
induction x, y <;> simp [f, *]
* Add support for `casesOn` applications to structural and well-founded recursion modules.
This feature is useful when writing definitions using tactics. Example:
```lean
inductive Foo where
| a | b | c
| pair: Foo × Foo → Foo
def Foo.deq (a b : Foo) : Decidable (a = b) := by
cases a <;> cases b
any_goals apply isFalse Foo.noConfusion
any_goals apply isTrue rfl
case pair a b =>
let (a₁, a₂) := a
let (b₁, b₂) := b
exact match deq a₁ b₁, deq a₂ b₂ with
| isTrue h₁, isTrue h₂ => isTrue (by rw [h₁,h₂])
| isFalse h₁, _ => isFalse (fun h => by cases h; cases (h₁ rfl))
| _, isFalse h₂ => isFalse (fun h => by cases h; cases (h₂ rfl))
Option
is again a monad. The auxiliary type OptionM
has been removed. See Zulip thread.
Improve split
tactic. It used to fail on match
expressions of the form match h : e with ...
where e
is not a free variable.
The failure used to occur during generalization.
New encoding for match
-expressions that use the h :
notation for discriminants. The information is not lost during delaboration,
and it is the foundation for a better split
tactic. at delaboration time. Example:
#print Nat.decEq
/-
protected def Nat.decEq : (n m : Nat) → Decidable (n = m) :=
fun n m =>
match h : Nat.beq n m with
| true => isTrue (_ : n = m)
| false => isFalse (_ : ¬n = m)
-/
exists
tactic is now takes a comma separated list of terms.
Add dsimp
and dsimp!
tactics. They guarantee the result term is definitionally equal, and only apply
rfl
-theorems.
Fix binder information for match
patterns that use definitions tagged with [matchPattern]
(e.g., Nat.add
).
We now have proper binder information for the variable y
in the following example.
def f (x : Nat) : Nat :=
match x with
| 0 => 1
| y + 1 => y
(Fix) the default value for structure fields may now depend on the structure parameters. Example: ```lean structure Something (i: Nat) where n1: Nat := 1 n2: Nat := 1 + i
def s : Something 10 := {} example : s.n2 = 11 := rfl
* Apply `rfl` theorems at the `dsimp` auxiliary method used by `simp`. `dsimp` can be used anywhere in an expression
because it preserves definitional equality.
* Refine auto bound implicit feature. It does not consider anymore unbound variables that have the same
name of a declaration being defined. Example:
```lean
def f : f → Bool := -- Error at second `f`
fun _ => true
inductive Foo : List Foo → Type -- Error at second `Foo`
| x : Foo []
Before this refinement, the declarations above would be accepted and the
second f
and Foo
would be treated as auto implicit variables. That is,
f : {f : Sort u} → f → Bool
, and
Foo : {Foo : Type u} → List Foo → Type
.
lean
inductive List (α : Type u) where
| nil : List α --
List` is not highlighted as a variable anymore
| cons (head : α) (tail : List α) : List αdef List.map (f : α → β) : List α → List β
| [] => []
| a::as => f a :: map f as -- `map` is not highlighted as a variable anymore
* Add `autoUnfold` option to `Lean.Meta.Simp.Config`, and the following macros
- `simp!` for `simp (config := { autoUnfold := true })`
- `simp_arith!` for `simp (config := { autoUnfold := true, arith := true })`
- `simp_all!` for `simp_all (config := { autoUnfold := true })`
- `simp_all_arith!` for `simp_all (config := { autoUnfold := true, arith := true })`
When the `autoUnfold` is set to true, `simp` tries to unfold the following kinds of definition
- Recursive definitions defined by structural recursion.
- Non-recursive definitions where the body is a `match`-expression. This
kind of definition is only unfolded if the `match` can be reduced.
Example:
```lean
def append (as bs : List α) : List α :=
match as with
| [] => bs
| a :: as => a :: append as bs
theorem append_nil (as : List α) : append as [] = as := by
induction as <;> simp_all!
theorem append_assoc (as bs cs : List α) : append (append as bs) cs = append as (append bs cs) := by
induction as <;> simp_all!
Add save
tactic for creating checkpoints more conveniently. Example:
example : <some-proposition> := by
tac_1
tac_2
save
tac_3
...
is equivalent to
example : <some-proposition> := by
checkpoint
tac_1
tac_2
tac_3
...
Remove support for {}
annotation from inductive datatype constructors. This annotation was barely used, and we can control the binder information for parameter bindings using the new inductive family indices to parameter promotion. Example: the following declaration using {}
inductive LE' (n : Nat) : Nat → Prop where
| refl {} : LE' n n -- Want `n` to be explicit
| succ : LE' n m → LE' n (m+1)
can now be written as
inductive LE' : Nat → Nat → Prop where
| refl (n : Nat) : LE' n n
| succ : LE' n m → LE' n (m+1)
In both cases, the inductive family has one parameter and one index.
Recall that the actual number of parameters can be retrieved using the command #print
.
Remove support for {}
annotation in the structure
command.
Several improvements to LSP server. Examples: "jump to definition" in mutually recursive sections, fixed incorrect hover information in "match"-expression patterns, "jump to definition" for pattern variables, fixed auto-completion in function headers, etc.
In macro ... xs:p* ...
and similar macro bindings of combinators, xs
now has the correct type Array Syntax
Identifiers in syntax patterns now ignore macro scopes during matching.
Improve binder names for constructor auto implicit parameters. Example, given the inductive datatype
inductive Member : α → List α → Type u
| head : Member a (a::as)
| tail : Member a bs → Member a (b::bs)
before:
#check @Member.head
-- @Member.head : {x : Type u_1} → {a : x} → {as : List x} → Member a (a :: as)
now:
#check @Member.head
-- @Member.head : {α : Type u_1} → {a : α} → {as : List α} → Member a (a :: as)
Improve error message when constructor parameter universe level is too big.
Add support for for h : i in [start:stop] do ..
where h : i ∈ [start:stop]
. This feature is useful for proving
termination of functions such as:
```lean
inductive Expr where
| app (f : String) (args : Array Expr)
def Expr.size (e : Expr) : Nat := Id.run do
match e with
| app f args =>
let mut sz := 1
for h : i in [: args.size] do
-- h.upper : i < args.size
sz := sz + size (args.get ⟨i, h.upper⟩)
return sz
* Add tactic `case'`. It is similar to `case`, but does not admit the goal on failure.
For example, the new tactic is useful when writing tactic scripts where we need to use `case'`
at `first | ... | ...`, and we want to take the next alternative when `case'` fails.
* Add tactic macro
```lean
macro "stop" s:tacticSeq : tactic => `(repeat sorry)
See discussion on Zulip.
When displaying goals, we do not display inaccessible proposition names if they do not have forward dependencies. We still display their types. For example, the goal
case node.inl.node
β : Type u_1
b : BinTree β
k : Nat
v : β
left : Tree β
key : Nat
value : β
right : Tree β
ihl : BST left → Tree.find? (Tree.insert left k v) k = some v
ihr : BST right → Tree.find? (Tree.insert right k v) k = some v
h✝ : k < key
a✝³ : BST left
a✝² : ForallTree (fun k v => k < key) left
a✝¹ : BST right
a✝ : ForallTree (fun k v => key < k) right
⊢ BST left
is now displayed as ```lean case node.inl.node β : Type u_1 b : BinTree β k : Nat v : β left : Tree β key : Nat value : β right : Tree β ihl : BST left → Tree.find? (Tree.insert left k v) k = some v ihr : BST right → Tree.find? (Tree.insert right k v) k = some v
: k < key : BST left : ForallTree (fun k v => k < key) left : BST right : ForallTree (fun k v => key < k) right ⊢ BST left ```
The hypothesis name is now optional in the by_cases
tactic.
Fix inconsistency between syntax
and kind names.
The node kinds numLit
, charLit
, nameLit
, strLit
, and scientificLit
are now called
num
, char
, name
, str
, and scientific
respectively. Example: we now write
macro_rules | `($n:num) => `("hello")
instead of
macro_rules | `($n:numLit) => `("hello")
(Experimental) New checkpoint <tactic-seq>
tactic for big interactive proofs.
Rename tactic nativeDecide
=> native_decide
.
Antiquotations are now accepted in any syntax. The incQuotDepth
syntax
parser is therefore obsolete and has been removed.
Renamed tactic nativeDecide
=> native_decide
.
"Cleanup" local context before elaborating a match
alternative right-hand-side. Examples:
``lean
example (x : Nat) : Nat :=
match g x with
| (a, b) => _ -- Local context does not contain the auxiliary
_discr := g x` anymore
example (x : Nat × Nat) (h : x.1 > 0) : f x > 0 := by
match x with
| (a, b) => _ -- Local context does not contain the `h✝ : x.fst > 0` anymore
* Improve `let`-pattern (and `have`-pattern) macro expansion. In the following example,
```lean
example (x : Nat × Nat) : f x > 0 := by
let (a, b) := x
done
The resulting goal is now ... |- f (a, b) > 0
instead of ... |- f x > 0
.
Add cross-compiled aarch64 Linux and aarch64 macOS releases.
Add tutorial-like examples to our documentation, rendered using LeanInk+Alectryon.
simp
now takes user-defined simp-attributes. You can define a new simp
attribute by creating a file (e.g., MySimp.lean
) containing
```lean
import Lean
open Lean.Metainitialize my_ext : SimpExtension ← registerSimpAttr `my_simp "my own simp attribute"
If you don't need to access `my_ext`, you can also use the macro
```lean
import Lean
register_simp_attr my_simp "my own simp attribute"
Recall that the new simp
attribute is not active in the Lean file where it was defined.
Here is a small example using the new feature.
import MySimp
def f (x : Nat) := x + 2
def g (x : Nat) := x + 1
@[my_simp] theorem f_eq : f x = x + 2 := rfl
@[my_simp] theorem g_eq : g x = x + 1 := rfl
example : f x + g x = 2*x + 3 := by
simp_arith [my_simp]
match
syntax: multiple left-hand-sides in a single alternative. Example:
lean
def fib : Nat → Nat
| 0 | 1 => 1
| n+2 => fib n + fib (n+1)
This feature was discussed at issue 371. It was implemented as a macro expansion. Thus, the following is accepted.
```lean
inductive StrOrNum where
| S (s : String)
| I (i : Int)def StrOrNum.asString (x : StrOrNum) :=
match x with
| I a | S a => toString a
* Improve `#eval` command. Now, when it fails to synthesize a `Lean.MetaEval` instance for the result type, it reduces the type and tries again. The following example now works without additional annotations
```lean
def Foo := List Nat
def test (x : Nat) : Foo :=
[x, x+1, x+2]
#eval test 4
rw
tactic can now apply auto-generated equation theorems for a given definition. Example:
example (a : Nat) (h : n = 1) : [a].length = n := by
rw [List.length]
trace_state -- .. |- [].length + 1 = n
rw [List.length]
trace_state -- .. |- 0 + 1 = n
rw [h]
Extend dot-notation x.field
for arrow types. If type of x
is an arrow, we look up for Function.field
.
For example, given f : Nat → Nat
and g : Nat → Nat
, f.comp g
is now notation for Function.comp f g
.
The new .<identifier>
notation is now also accepted where a function type is expected.
example (xs : List Nat) : List Nat := .map .succ xs
example (xs : List α) : Std.RBTree α ord := xs.foldl .insert ∅
Support notation let <pattern> := <expr> | <else-case>
in do
blocks.
Remove support for "auto" pure
. In the Zulip thread, the consensus seemed to be that "auto" pure
is more confusing than it's worth.
Remove restriction in congr
theorems that all function arguments on the left-hand-side must be free variables. For example, the following theorem is now a valid congr
theorem.
@[congr]
theorem dep_congr [DecidableEq ι] {p : ι → Set α} [∀ i, Inhabited (p i)] :
∀ {i j} (h : i = j) (x : p i) (y : α) (hx : x = y), Pi.single (f := (p ·)) i x = Pi.single (f := (p ·)) j ⟨y, hx ▸ h ▸ x.2⟩ :=
Improve elaboration postponement heuristic when expected type is a metavariable. Lean now reduces the expected type before performing the test.
Remove deprecated leanpkg in favor of Lake now bundled with Lean.
Various improvements to go-to-definition & find-all-references accuracy.
Auto generated congruence lemmas with support for casts on proofs and Decidable
instances (see wishlist).
Rename option autoBoundImplicitLocal
=> autoImplicit
.
Relax auto-implicit restrictions. The command set_option relaxedAutoImplicit false
disables the relaxations.
contradiction
tactic now closes the goal if there is a False.elim
application in the target.
Renamed tatic byCases
=> by_cases
(motivation: enforcing naming convention).
Local instances occurring in patterns are now considered by the type class resolution procedure. Example:
def concat : List ((α : Type) × ToString α × α) → String
| [] => ""
| ⟨_, _, a⟩ :: as => toString a ++ concat as
Notation for providing the motive for match
expressions has changed.
before:
match x, rfl : (y : Nat) → x = y → Nat with
| 0, h => ...
| x+1, h => ...
now:
match (motive := (y : Nat) → x = y → Nat) x, rfl with
| 0, h => ...
| x+1, h => ...
With this change, the notation for giving names to equality proofs in match
-expressions is not whitespace sensitive anymore. That is,
we can now write
match h : sort.swap a b with
| (r₁, r₂) => ... -- `h : sort.swap a b = (r₁, r₂)`
(generalizing := true)
is the default behavior for match
expressions even if the expected type is not a proposition. In the following example, we used to have to include (generalizing := true)
manually.
```lean
inductive Fam : Type → Type 1 where
| any : Fam α
| nat : Nat → Fam Nat
example (a : α) (x : Fam α) : α :=
match x with
| Fam.any => a
| Fam.nat n => n
* We now use `PSum` (instead of `Sum`) when compiling mutually recursive definitions using well-founded recursion.
* Better support for parametric well-founded relations. See [issue #1017](https://github.com/leanprover/lean4/issues/1017). This change affects the low-level `termination_by'` hint because the fixed prefix of the function parameters in not "packed" anymore when constructing the well-founded relation type. For example, in the following definition, `as` is part of the fixed prefix, and is not packed anymore. In previous versions, the `termination_by'` term would be written as `measure fun ⟨as, i, _⟩ => as.size - i`
```lean
def sum (as : Array Nat) (i : Nat) (s : Nat) : Nat :=
if h : i < as.size then
sum as (i+1) (s + as.get ⟨i, h⟩)
else
s
termination_by' measure fun ⟨i, _⟩ => as.size - i
Add while <cond> do <do-block>
, repeat <do-block>
, and repeat <do-block> until <cond>
macros for do
-block. These macros are based on partial
definitions, and consequently are useful only for writing programs we don't want to prove anything about.
Add arith
option to Simp.Config
, the macro simp_arith
expands to simp (config := { arith := true })
. Only Nat
and linear arithmetic is currently supported. Example:
example : 0 < 1 + x ∧ x + y + 2 ≥ y + 1 := by
simp_arith
Add fail <string>?
tactic that always fail.
Add support for acyclicity at dependent elimination. See issue #1022.
Add trace <string>
tactic for debugging purposes.
Add nontrivial SizeOf
instance for types Unit → α
, and add support for them in the auto-generated SizeOf
instances for user-defined inductive types. For example, given the inductive datatype
inductive LazyList (α : Type u) where
| nil : LazyList α
| cons (hd : α) (tl : LazyList α) : LazyList α
| delayed (t : Thunk (LazyList α)) : LazyList α
we now have sizeOf (LazyList.delayed t) = 1 + sizeOf t
instead of sizeOf (LazyList.delayed t) = 2
.
Add support for guessing (very) simple well-founded relations when proving termination. For example, the following function does not require a termination_by
annotation anymore.
def Array.insertAtAux (i : Nat) (as : Array α) (j : Nat) : Array α :=
if h : i < j then
let as := as.swap! (j-1) j;
insertAtAux i as (j-1)
else
as
Add support for for h : x in xs do ...
notation where h : x ∈ xs
. This is mainly useful for showing termination.
Auto implicit behavior changed for inductive families. An auto implicit argument occurring in inductive family index is also treated as an index (IF it is not fixed, see next item). For example
inductive HasType : Index n → Vector Ty n → Ty → Type where
is now interpreted as
inductive HasType : {n : Nat} → Index n → Vector Ty n → Ty → Type where
To make the previous feature more convenient to use, we promote a fixed prefix of inductive family indices to parameters. For example, the following declaration is now accepted by Lean
inductive Lst : Type u → Type u
| nil : Lst α
| cons : α → Lst α → Lst α
and α
in Lst α
is a parameter. The actual number of parameters can be inspected using the command #print Lst
. This feature also makes sure we still accept the declaration
inductive Sublist : List α → List α → Prop
| slnil : Sublist [] []
| cons l₁ l₂ a : Sublist l₁ l₂ → Sublist l₁ (a :: l₂)
| cons2 l₁ l₂ a : Sublist l₁ l₂ → Sublist (a :: l₁) (a :: l₂)
Added auto implicit "chaining". Unassigned metavariables occurring in the auto implicit types now become new auto implicit locals. Consider the following example:
inductive HasType : Fin n → Vector Ty n → Ty → Type where
| stop : HasType 0 (ty :: ctx) ty
| pop : HasType k ctx ty → HasType k.succ (u :: ctx) ty
ctx
is an auto implicit local in the two constructors, and it has type ctx : Vector Ty ?m
. Without auto implicit "chaining", the metavariable ?m
will remain unassigned. The new feature creates yet another implicit local n : Nat
and assigns n
to ?m
. So, the declaration above is shorthand for
inductive HasType : {n : Nat} → Fin n → Vector Ty n → Ty → Type where
| stop : {ty : Ty} → {n : Nat} → {ctx : Vector Ty n} → HasType 0 (ty :: ctx) ty
| pop : {n : Nat} → {k : Fin n} → {ctx : Vector Ty n} → {ty : Ty} → HasType k ctx ty → HasType k.succ (u :: ctx) ty
Eliminate auxiliary type annotations (e.g, autoParam
and optParam
) from recursor minor premises and projection declarations. Consider the following example
```lean
structure A :=
x : Nat
h : x = 1 := by trivial
example (a : A) : a.x = 1 := by
have aux := a.h
-- `aux` has now type `a.x = 1` instead of `autoParam (a.x = 1) auto✝`
exact aux
example (a : A) : a.x = 1 := by
cases a with
| mk x h =>
-- `h` has now type `x = 1` instead of `autoParam (x = 1) auto✝`
assumption
* We now accept overloaded notation in patterns, but we require the set of pattern variables in each alternative to be the same. Example:
```lean
inductive Vector (α : Type u) : Nat → Type u
| nil : Vector α 0
| cons : α → Vector α n → Vector α (n+1)
infix:67 " :: " => Vector.cons -- Overloading the `::` notation
def head1 (x : List α) (h : x ≠ []) : α :=
match x with
| a :: as => a -- `::` is `List.cons` here
def head2 (x : Vector α (n+1)) : α :=
match x with
| a :: as => a -- `::` is `Vector.cons` here
.<identifier>
based on Swift. The namespace is inferred from the expected type. See issue #944. Examples:
```lean
def f (x : Nat) : Except String Nat :=
if x > 0 then
.ok x
else
.error "x is zero"namespace Lean.Elab open Lsp
def identOf : Info → Option (RefIdent × Bool)
| .ofTermInfo ti => match ti.expr with
| .const n .. => some (.const n, ti.isBinder)
| .fvar id .. => some (.fvar id, ti.isBinder)
| _ => none
| .ofFieldInfo fi => some (.const fi.projName, false)
| _ => none
def isImplicit (bi : BinderInfo) : Bool :=
bi matches .implicit
end Lean.Elab ```