Initial

BidirTT/Context.lean

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+import BidirTT.Value
+
+namespace BidirTT
+
+structure Cxt where
+  env   : Env
+  types : List (Name × Val)
+  lvl   : Lvl
+  deriving Inhabited
+
+def Cxt.empty : Cxt := ⟨[], [], 0⟩
+
+def Cxt.bind (cxt : Cxt) (x : Name) (a : Val) : Cxt :=
+  { env   := .var cxt.lvl :: cxt.env
+  , types := (x, a) :: cxt.types
+  , lvl   := cxt.lvl + 1 }
+
+def Cxt.define (cxt : Cxt) (x : Name) (v a : Val) : Cxt :=
+  { env   := v :: cxt.env
+  , types := (x, a) :: cxt.types
+  , lvl   := cxt.lvl + 1 }
+
+private def lookupGo : Name → List (Name × Val) → Nat → Option (Nat × Val)
+  | _, [],              _ => none
+  | x, (y, a) :: rest,  i => if x == y then some (i, a) else lookupGo x rest (i+1)
+
+def Cxt.lookup (cxt : Cxt) (x : Name) : Option (Nat × Val) :=
+  lookupGo x cxt.types 0
+
+end BidirTT