2 files changed, 24 insertions, 2 deletions
diff --git a/lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs b/lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs
index 290839e..8b24f8b 100644
--- a/lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs
+++ b/lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs
@@ -1,8 +1,9 @@
 {-# LANGUAGE LambdaCase #-}
+
 module Minilang.Lambda.DeBruijn where
 
 import Data.List (elemIndex)
-import Data.Text (Text, unpack, pack)
+import Data.Text (Text)
 import Minilang.Lambda.Eval (Term)
 import qualified Minilang.Lambda.Eval as Eval
 
@@ -13,6 +14,12 @@ data DeBruijn ann
   | App (DeBruijn ann) (DeBruijn ann)
   deriving (Show, Read, Eq)
 
+type Env ann = [(Text, DeBruijn ann)]
+
+newEnv :: Env ann
+newEnv = []
+
+
 fromDeBruijn :: DeBruijn Text -> Term
 fromDeBruijn = \case
   FV x -> Eval.Var x
@@ -40,6 +47,16 @@ eval (App f a) =
     f' -> App f' a
 eval term = term
 
+eval' :: Env ann -> DeBruijn ann -> DeBruijn ann
+eval' env (FV v) = case lookup v env of
+  Just term -> term
+  Nothing -> FV v
+eval' env (App f a) =
+  case eval' env f of
+    Lam _ body -> eval' env (substitute 0 a body)
+    f' -> App f' a
+eval' _ term = term
+
 substitute :: Int -> DeBruijn ann -> DeBruijn ann -> DeBruijn ann
 substitute n arg term = case term of
   FV x -> FV x
diff --git a/lambda-calcul/haskell/test/Minilang/Lambda/DeBruijnSpec.hs b/lambda-calcul/haskell/test/Minilang/Lambda/DeBruijnSpec.hs
index cff047d..85c9d6b 100644
--- a/lambda-calcul/haskell/test/Minilang/Lambda/DeBruijnSpec.hs
+++ b/lambda-calcul/haskell/test/Minilang/Lambda/DeBruijnSpec.hs
@@ -1,7 +1,7 @@
 {-# LANGUAGE TypeApplications #-}
 module Minilang.Lambda.DeBruijnSpec where
 
-import Minilang.Lambda.DeBruijn (DeBruijn (..), eval, toDeBruijn)
+import Minilang.Lambda.DeBruijn (DeBruijn (..), eval, toDeBruijn, eval')
 import qualified Minilang.Lambda.Eval as Eval
 import Test.Hspec (Spec, it, shouldBe)
 import Data.Text (Text)
@@ -18,3 +18,8 @@ spec = do
     let term = App (App (Lam "x" (Lam "y" (Var "x" 1))) (FV "z")) (FV "t")
 
     eval @Text term `shouldBe` FV "z"
+
+  it "evaluates deBruijn term in env" $ do
+    let term = App (FV "z") (FV "t")
+        env = [("z", toDeBruijn $ Eval.Lam "x" (Eval.Var "x"))]
+    eval' @Text env term `shouldBe` FV "t"