Commit graph

20 commits

Author SHA1 Message Date
Leonardo de Moura
603dafbaf7 refactor(kernel): remove 'let'-expressions
We simulate it in the following way:
1- An opaque 'let'-expressions (let x : t := v in b) is encoded as
      ((fun (x : t), b) v)
   We also use a macro (let-macro) to mark this pattern.
   Thus, the pretty-printer knows how to display it correctly.

2- Transparent 'let'-expressions are eagerly expanded by the parser.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-06-24 16:27:27 -07:00
Leonardo de Moura
40b3129e7b refactor(kernel): improve names
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-05-16 11:28:05 -07:00
Leonardo de Moura
ff9004dae2 refactor(kernel): add level normalizer, is_equivalent predicate, switch to is_equivalent in the type checker, fix bugs in is_lt predicate
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-05-11 18:05:02 -07:00
Leonardo de Moura
503d8dfa9e feat(kernel): add global universe level
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-05-06 16:13:29 -07:00
Leonardo de Moura
4842ae4fc7 refactor(kernel): store macro arguments in the macro_expr
Before this commit, we "stored" macro arguments using applications.
This representation had some issues. Suppose we use [m a] to denote a macro
application. In the old representation, ([m a] b) and [m a b] would have
the same representation. Another problem is that some procedures (e.g., type inference)
would not have a clean implementation.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-04-25 15:02:56 -07:00
Leonardo de Moura
bc8379256a refactor(kernel): remove pairs from kernel
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-04-17 10:52:07 -07:00
Leonardo de Moura
e0ef6b2e9a refactor(library): monotonic total order on terms
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-03-18 10:27:56 -07:00
Leonardo de Moura
6d7ec9d7b6 refactor(kernel): add heterogeneous equality back to expr
The main motivation is that we will be able to move equalities between universes.

For example, suppose we have
    A : (Type i)
    B : (Type i)
    H : @eq (Type j) A B
where j > i

We didn't find any trick for deducing (@eq (Type i) A B) from H.
Before this commit, heterogeneous equality as a constant with type

   heq : {A B : (Type U)} : A -> B -> Bool

So, from H, we would only be able to deduce

   (@heq (Type j) (Type j) A B)

Not being able to move the equality back to a smaller universe is
problematic in several cases. I list some instances in the end of the commit message.

With this commit, Heterogeneous equality is a special kind of expression.
It is not a constant anymore. From H, we can deduce

   H1 : A == B

That is, we are essentially "erasing" the universes when we move to heterogeneous equality.
Now, since A and B have (Type i), we can deduce (@eq (Type i) A B) from H1. The proof term is

  (to_eq (Type i) A B (to_heq (Type j) A B H))  :  (@eq (Type i) A B)

So, it remains to explain why we need this feature.

For example, suppose we want to state the Pi extensionality axiom.

axiom hpiext {A A' : (Type U)} {B : A → (Type U)} {B' : A' → (Type U)} :
      A = A' → (∀ x x', x == x' → B x == B' x') → (∀ x, B x) == (∀ x, B' x)

This axiom produces an "inflated" equality at (Type U) when we treat heterogeneous
equality as a constant. The conclusion

     (∀ x, B x) == (∀ x, B' x)

is syntax sugar for

   (@heq (Type U) (Type U) (∀ x : A, B x) (∀ x : A', B' x))

Even if A, A', B, B' live in a much smaller universe.

As I described above, it doesn't seem to be a way to move this equality back to a smaller universe.

So, if we wanted to keep the heterogeneous equality as a constant, it seems we would
have to support axiom schemas. That is, hpiext would be parametrized by the universes where
A, A', B and B'. Another possibility would be to have universe polymorphism like Agda.
None of the solutions seem attractive.

So, we decided to have heterogeneous equality as a special kind of expression.
And use the trick above to move equalities back to the right universe.

BTW, the parser is not creating the new heterogeneous equalities yet.
Moreover, kernel.lean still contains a constant name heq2 that is the heterogeneous
equality as a constant.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-02-07 10:28:10 -08:00
Leonardo de Moura
8eec289ce1 feat(kernel): add dependent pairs
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-02-03 16:52:49 -08:00
Leonardo de Moura
6bcd8e3ee5 fix(library/expr_lt): use expression depth instead of size to obtain a monotonic total order on terms
It is not incorrect to use size, but it can easily overflow due to sharing.
The following script demonstrates the problem:

local f = Const("f")
local a = Const("a")
function mk_shared(d)
   if d == 0 then
      return a
   else
      local c = mk_shared(d-1)
      return f(c, c)
   end
end
print(mk_shared(33):size())

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-01-20 17:40:49 -08:00
Leonardo de Moura
6a63ef3bc5 feat(library/expr_lt): make sure the total order on terms is monotonic
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-01-20 13:07:18 -08:00
Leonardo de Moura
a43020b31b refactor(kernel): remove heterogeneous equality
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-01-16 17:39:12 -08:00
Leonardo de Moura
411f14415d feat(builtin): automatically generate Lean/C++ interface for builtin theories
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2014-01-09 18:09:53 -08:00
Leonardo de Moura
3e1fd06903 refactor(kernel/expr): remove 'null' expression, and operator bool for expression
After this commit, a value of type 'expr' cannot be a reference to nullptr.
This commit also fixes several bugs due to the use of 'null' expressions.

TODO: do the same for kernel objects, sexprs, etc.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2013-12-07 23:21:10 -08:00
Leonardo de Moura
8e56726116 fix(library/expr_lt): fix bug when using hash codes
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2013-11-14 13:18:33 -08:00
Leonardo de Moura
31abc00db8 chore(*): add LCOV_EXCL_LINE to lean_unreachable statements
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2013-11-11 09:19:38 -08:00
Leonardo de Moura
59914a36f3 refactor(metavar): reorganize and simplify metavariables
- Use hierarchical names instead of unsigned integers to identify metavariables.
- Associate type with metavariable.
- Replace metavar_env with substitution.
- Rename meta_ctx --> local_ctx
- Rename meta_entry --> local_entry
- Disable old elaborator
- Rename unification_problems to unification_constraints
- Add metavar_generator
- Fix metavar unit tests
- Modify type checker to use metavar_generator
- Fix placeholder module

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2013-10-22 08:15:36 -07:00
Leonardo de Moura
db4e5ab0ad feat(expr_lt): improve expr_lt performance by using hash codes, and add more tests
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2013-09-25 21:59:58 -07:00
Leonardo de Moura
6477708d78 refactor(debug): improve lean_unreachable(), now we can avoid 'fake' return statements
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2013-09-25 21:27:20 -07:00
Leonardo de Moura
ba0528c298 Implement total order on expressions
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2013-09-24 12:16:32 -07:00