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module Core.Var
import Core.Context
import Core.Thinning
%prefix_record_projections off
-- Variables -------------------------------------------------------------------
data IsVar : Nat -> Context -> Type where
Here : IsVar 0 (sx :< n)
There : IsVar k sx -> IsVar (S k) (sx :< n)
export
record Var (sx : Context) where
constructor MakeVar
index : Nat
0 prf : IsVar index sx
%name IsVar prf
%name Var i, j, k
-- Constructors ----------------------------------------------------------------
export
here : Var (sx :< n)
here = MakeVar 0 Here
export
there : Var sx -> Var (sx :< n)
there (MakeVar index prf) = MakeVar (S index) (There prf)
-- Views -----------------------------------------------------------------------
namespace View
public export
data View : Var sx -> Type where
Here : View Core.Var.here
There : (i : Var sx) -> View (there i)
%name View.View view
export
view : (i : Var sx) -> View i
view (MakeVar 0 Here) = Here
view (MakeVar (S k) (There prf)) = There (MakeVar k prf)
-- Operations ------------------------------------------------------------------
doWkn : Var sx -> {0 thin : sx `Thins` sy} -> View thin -> Var sy
doWkn i (Id sy) = i
doWkn i (Drop thin n) = there $ doWkn i (view thin)
doWkn (MakeVar 0 Here) (Keep thin n _) = here
doWkn (MakeVar (S k) (There prf)) (Keep thin n _) = there $ doWkn (MakeVar k prf) (view thin)
export
wkn : Var sx -> sx `Thins` sy -> Var sy
wkn i thin = doWkn i (view thin)
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