mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-12-22 19:21:39 +03:00
89 lines
3.0 KiB
Idris
89 lines
3.0 KiB
Idris
module Data.Vect.Elem
|
|
|
|
import Data.Vect
|
|
import Decidable.Equality
|
|
|
|
%default total
|
|
|
|
--------------------------------------------------------------------------------
|
|
-- Vector membership proof
|
|
--------------------------------------------------------------------------------
|
|
|
|
||| A proof that some element is found in a vector
|
|
public export
|
|
data Elem : a -> Vect k a -> Type where
|
|
Here : Elem x (x::xs)
|
|
There : (later : Elem x xs) -> Elem x (y::xs)
|
|
|
|
export
|
|
Uninhabited (Here = There e) where
|
|
uninhabited Refl impossible
|
|
|
|
export
|
|
Uninhabited (There e = Here) where
|
|
uninhabited Refl impossible
|
|
|
|
export
|
|
Uninhabited (Elem x []) where
|
|
uninhabited Here impossible
|
|
|
|
export
|
|
Uninhabited (x = z) => Uninhabited (Elem z xs) => Uninhabited (Elem z $ x::xs) where
|
|
uninhabited Here @{xz} = uninhabited Refl @{xz}
|
|
uninhabited (There y) = uninhabited y
|
|
|
|
||| An item not in the head and not in the tail is not in the Vect at all
|
|
export
|
|
neitherHereNorThere : Not (x = y) -> Not (Elem x xs) -> Not (Elem x (y :: xs))
|
|
neitherHereNorThere xneqy xninxs Here = xneqy Refl
|
|
neitherHereNorThere xneqy xninxs (There xinxs) = xninxs xinxs
|
|
|
|
||| A decision procedure for Elem
|
|
public export
|
|
isElem : DecEq a => (x : a) -> (xs : Vect n a) -> Dec (Elem x xs)
|
|
isElem x [] = No uninhabited
|
|
isElem x (y::xs) with (decEq x y)
|
|
isElem x (x::xs) | (Yes Refl) = Yes Here
|
|
isElem x (y::xs) | (No xneqy) with (isElem x xs)
|
|
isElem x (y::xs) | (No xneqy) | (Yes xinxs) = Yes (There xinxs)
|
|
isElem x (y::xs) | (No xneqy) | (No xninxs) = No (neitherHereNorThere xneqy xninxs)
|
|
|
|
public export
|
|
replaceElem : (xs : Vect k t) -> Elem x xs -> (y : t) -> (ys : Vect k t ** Elem y ys)
|
|
replaceElem (x::xs) Here y = (y :: xs ** Here)
|
|
replaceElem (x::xs) (There xinxs) y with (replaceElem xs xinxs y)
|
|
replaceElem (x::xs) (There xinxs) y | (ys ** yinys) = (x :: ys ** There yinys)
|
|
|
|
public export
|
|
replaceByElem : (xs : Vect k t) -> Elem x xs -> t -> Vect k t
|
|
replaceByElem (x::xs) Here y = y :: xs
|
|
replaceByElem (x::xs) (There xinxs) y = x :: replaceByElem xs xinxs y
|
|
|
|
public export
|
|
mapElem : {0 xs : Vect k t} -> {0 f : t -> u} ->
|
|
(1 _ : Elem x xs) -> Elem (f x) (map f xs)
|
|
mapElem Here = Here
|
|
mapElem (There e) = There (mapElem e)
|
|
|
|
||| Remove the element at the given position.
|
|
|||
|
|
||| @xs The vector to be removed from
|
|
||| @p A proof that the element to be removed is in the vector
|
|
public export
|
|
dropElem : {k : _} -> (xs : Vect (S k) t) -> Elem x xs -> Vect k t
|
|
dropElem (x::ys) Here = ys
|
|
dropElem {k = S k} (x::ys) (There later) = x :: dropElem ys later
|
|
|
|
||| Erase the indices, returning the bounded numeric position of the element
|
|
public export
|
|
elemToFin : {0 xs : Vect n a} -> Elem x xs -> Fin n
|
|
elemToFin Here = FZ
|
|
elemToFin (There p) = FS (elemToFin p)
|
|
|
|
||| Find the element with a proof at a given bounded position
|
|
public export
|
|
indexElem : (1 _ : Fin n) -> (xs : Vect n a) -> (x ** Elem x xs)
|
|
indexElem FZ (y::_) = (y ** Here)
|
|
indexElem (FS n) (_::ys) = let (x ** p) = indexElem n ys in
|
|
(x ** There p)
|