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feat(library/coercion): add simple trick for defining coercions to function-class in a convenient way, closes #31

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Leonardo de Moura 2014-09-09 14:35:48 -07:00
parent abdd784729
commit bd1bc336fb
3 changed files with 10 additions and 13 deletions
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7
library/hott/equiv.lean
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@ -45,17 +45,12 @@ Equiv_mk : Π
(equiv_isequiv : IsEquiv equiv_fun), (equiv_isequiv : IsEquiv equiv_fun),
Equiv A B Equiv A B
definition equiv_fun {A B : Type} (e : Equiv A B) : A → B := definition equiv_fun [coercion] {A B : Type} (e : Equiv A B) : A → B :=
Equiv.rec (λequiv_fun equiv_isequiv, equiv_fun) e Equiv.rec (λequiv_fun equiv_isequiv, equiv_fun) e
-- TODO: use a type class instead?
coercion equiv_fun : Equiv
definition equiv_isequiv [coercion] {A B : Type} (e : Equiv A B) : IsEquiv (equiv_fun e) := definition equiv_isequiv [coercion] {A B : Type} (e : Equiv A B) : IsEquiv (equiv_fun e) :=
Equiv.rec (λequiv_fun equiv_isequiv, equiv_isequiv) e Equiv.rec (λequiv_fun equiv_isequiv, equiv_isequiv) e
-- coercion equiv_isequiv
-- TODO: better symbol -- TODO: better symbol
infix `<~>`:25 := Equiv infix `<~>`:25 := Equiv
notation e `⁻¹` := equiv_inv e notation e `⁻¹` := equiv_inv e

4
library/logic/classes/decidable.lean
View file

@ -99,7 +99,5 @@ end decidable
inductive decidable_eq [class] (A : Type) : Type := inductive decidable_eq [class] (A : Type) : Type :=
intro : (Π x y : A, decidable (x = y)) → decidable_eq A intro : (Π x y : A, decidable (x = y)) → decidable_eq A
theorem of_decidable_eq [instance] {A : Type} (H : decidable_eq A) (x y : A) : decidable (x = y) := theorem of_decidable_eq [instance] [coercion] {A : Type} (H : decidable_eq A) (x y : A) : decidable (x = y) :=
decidable_eq.rec (λ H, H) H x y decidable_eq.rec (λ H, H) H x y
coercion of_decidable_eq : decidable_eq

12
src/library/coercion.cpp
View file

@ -344,12 +344,16 @@ environment add_coercion(environment const & env, name const & f, io_state const
declaration d = env.get(f); declaration d = env.get(f);
expr t = d.get_type(); expr t = d.get_type();
check_pi(f, t); check_pi(f, t);
while (is_pi(binding_body(t))) optional<name> C;
while (is_pi(t)) {
expr d = get_app_fn(binding_domain(t));
if (is_constant(d))
C = const_name(d);
t = binding_body(t); t = binding_body(t);
expr C = get_app_fn(binding_domain(t)); }
if (!is_constant(C)) if (!C)
throw exception(sstream() << "invalid coercion, '" << f << "' cannot be used as a coercion"); throw exception(sstream() << "invalid coercion, '" << f << "' cannot be used as a coercion");
return add_coercion(env, f, const_name(C), ios); return add_coercion(env, f, *C, ios);
} }
optional<pair<name, unsigned>> is_coercion(environment const & env, name const & f) { optional<pair<name, unsigned>> is_coercion(environment const & env, name const & f) {