1 files changed, 101 insertions, 0 deletions
diff --git a/src/SOAS/Var.idr b/src/SOAS/Var.idr
new file mode 100644
index 0000000..f3129f9
--- /dev/null
+++ b/src/SOAS/Var.idr
@@ -0,0 +1,101 @@
+module SOAS.Var
+
+import SOAS.Context
+import SOAS.Family
+
+prefix 4 %%
+infixr 3 ~> , ~:>
+
+public export
+data (.varPos) : (ctx : type.Ctx) -> (0 x : String) -> type -> Type
+    where [search x]
+  Here  : (ctx :< (x :- ty)).varPos x ty
+  There : ctx.varPos x ty -> (ctx :< sy).varPos x ty
+
+public export
+data (.var) : type.Ctx -> type -> Type where
+  (%%) : (0 name : String) -> {auto pos : ctx.varPos name ty} -> ctx.var ty
+
+0
+(.name) : ctx.var ty -> String
+(%% name).name = name
+
+export
+(.pos) : (v : ctx.var ty) -> ctx.varPos v.name ty
+((%% name) {pos}).pos = pos
+
+export
+(.toVar) : (v : ctx.varPos x ty) -> ctx.var ty
+pos.toVar {x} = (%% x) {pos}
+
+export
+ThereVar : (v : ctx.var ty) -> (ctx :< ex).var ty
+ThereVar v = (%% v.name) {pos = There v.pos}
+
+public export
+Var : type.SortedFamily
+Var = flip (.var)
+
+public export 0
+(.subst) : {type : Type} -> type.SortedFamily -> type.Ctx -> type.Ctx -> Type
+f.subst ctx1 ctx2 = type.gensubst Var f ctx1 ctx2
+
+public export 0
+(.substNamed) : {type : Type} -> type.SortedFamily -> type.Ctx -> type.Ctx -> Type
+f.substNamed ctx1 ctx2 = {0 x : String} -> {0 ty : type} -> ctx1.varPos x ty -> f ty ctx2
+
+public export 0
+(~>) : {type : Type} -> (src, tgt : type.Ctx) -> Type
+(~>) = (Var).subst
+
+public export 0
+(~:>) : {type : Type} -> (src, tgt : type.Ctx) -> Type
+(~:>) = (Var).substNamed
+
+weakl : (ctx1, ctx2 : type.Ctx) -> ctx1 ~> (ctx1 ++ ctx2)
+weakl ctx1 [<] x = x
+weakl ctx1 (ctx2 :< z) x = ThereVar (weakl ctx1 ctx2 x)
+
+weakrNamed : (ctx1, ctx2 : type.Ctx) -> ctx2 ~:> (ctx1 ++ ctx2)
+weakrNamed ctx1 (ctx :< (x :- ty)) Here = (%% x) {pos = Here}
+weakrNamed ctx1 (ctx :< sy) (There pos) =
+  ThereVar $ weakrNamed ctx1 ctx pos
+
+weakr : (ctx1, ctx2 : type.Ctx) -> ctx2 ~> (ctx1 ++ ctx2)
+weakr ctx1 ctx2 ((%% name) {pos}) = weakrNamed ctx1 ctx2 pos
+
+(.copairPos) :
+  (0 x : type.SortedFamily) -> {auto length : ctx2.Erased} ->
+  x.subst ctx1 ctx -> x.subst ctx2 ctx -> x.substNamed (ctx1 ++ ctx2) ctx
+x.copairPos {length = Z} g1 g2 pos = g1 $ pos.toVar
+x.copairPos {length = S l} g1 g2 Here = g2 (Here .toVar)
+x.copairPos {length = S l} g1 g2 (There pos) =
+  x.copairPos g1 (g2 . ThereVar) pos
+
+(.copair) :
+  (0 x : type.SortedFamily) -> {auto length : ctx2.Erased} ->
+  x.subst ctx1 ctx -> x.subst ctx2 ctx -> x.subst (ctx1 ++ ctx2) ctx
+x.copair g1 g2 v = x.copairPos g1 g2 v.pos
+
+export
+extend :
+  (0 x : type.SortedFamily) ->
+  x ty ctx2 -> x.subst ctx1 ctx2 ->
+  x.subst (ctx1 :< (n :- ty)) ctx2
+extend x {ctx2, ty} u theta = x.copair {length = S Z} theta workaround -- (\case {Here => x})
+    where
+      workaround : x.subst [< (n :- ty)] ctx2
+      workaround ((%% _) {pos = Here}) = u
+
+public export 0
+(^) : (tgt, src : type.SortedFamily) -> type.SortedFamily
+(tgt ^ src) ty ctx = src.subst ctx -||> tgt ty
+
+public export 0
+Nil : type.SortedFamily -> type.SortedFamily
+Nil f = f ^ Var
+
+0
+(*) : (derivative, tangent : type.SortedFamily) -> type.SortedFamily
+(derivative * tangent) ty ctx =
+  (ctx' : type.Ctx ** (derivative ty ctx' , tangent.subst ctx' ctx))