From 91ae5eb9e16b00603c3dfa5ec123c64dd140765d Mon Sep 17 00:00:00 2001
From: Arnaud Bailly <arnaud@pankzsoft.com>
Date: Sun, 22 Mar 2026 08:49:18 +0100
Subject: Add integers parsing

---
 lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

(limited to 'lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs')

diff --git a/lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs b/lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs
index 025fd39..1e85ca6 100644
--- a/lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs
+++ b/lambda-calcul/haskell/src/Minilang/Lambda/DeBruijn.hs
@@ -4,12 +4,13 @@ module Minilang.Lambda.DeBruijn where
 
 import Data.List (elemIndex)
 import Data.Text (Text)
+import qualified Data.Text
 import Minilang.Lambda.Eval (Term)
 import qualified Minilang.Lambda.Eval as Eval
-import Debug.Trace (trace)
 
 data DeBruijn ann
   = FV Text
+  | FNum Int
   | Var ann Int
   | Lam ann (DeBruijn ann)
   | App (DeBruijn ann) (DeBruijn ann)
@@ -23,6 +24,7 @@ newEnv = []
 fromDeBruijn :: DeBruijn Text -> Term
 fromDeBruijn = \case
   FV x -> Eval.Var x
+  FNum n -> Eval.Num n
   Var s _ -> Eval.Var s
   Lam s body -> Eval.Lam s (fromDeBruijn body)
   App f a -> Eval.App (fromDeBruijn f) (fromDeBruijn a)
@@ -39,6 +41,8 @@ toDeBruijn term = go term []
       Lam x (go body (x : env))
     go (Eval.App f a) env =
       App (go f env) (go a env)
+    go (Eval.Num n) _env =
+      FNum n
 
 eval :: DeBruijn ann -> DeBruijn ann
 eval (App f a) =
@@ -64,6 +68,7 @@ substitute env n arg term = case term of
   FV x -> case lookup x env of
     Just term -> term
     Nothing -> FV x
+  FNum _ -> term
   Var t x
     | x == n -> arg
     | otherwise -> Var t x
@@ -73,6 +78,13 @@ substitute env n arg term = case term of
 pretty :: DeBruijn Text -> Text
 pretty = \case
   FV x -> x
+  FNum n -> showNum n
   Var s _ -> s
   Lam s body -> "(lam (" <> s <> ") " <> pretty body <> ")"
   App f a -> "(" <> pretty f <> " " <> pretty a <> ")"
+
+-- | Render an integer, using no space between '-' and digits for negative numbers.
+showNum :: Int -> Text
+showNum n
+  | n < 0     = "-" <> Data.Text.pack (show (abs n))
+  | otherwise = Data.Text.pack (show n)
-- 
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