From bb7b28a9e8a1a05d6d9af0f943a158a03a148190 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roman=20Smr=C5=BE?= <roman.smrz@seznam.cz>
Date: Thu, 9 Jul 2026 19:44:18 +0200
Subject: Expr data type

---
 src/Expr.hs | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 src/Expr.hs

(limited to 'src')

diff --git a/src/Expr.hs b/src/Expr.hs
new file mode 100644
index 0000000..fa17158
--- /dev/null
+++ b/src/Expr.hs
@@ -0,0 +1,51 @@
+module Expr (
+    Expr(..),
+    ExprContext(..),
+    getContext,
+
+    addDependency,
+    collectDependencies,
+
+    exprIO,
+) where
+
+import Data.Kind
+
+
+data Expr c a where
+    Pure :: a -> Expr c a
+    App :: Expr c (a -> b) -> Expr c a -> Expr c b
+    GetContext :: Expr c c
+    AddDependency :: ExprContext c => ExprDependency c -> Expr c a -> Expr c a
+    ExprIO :: IO a -> Expr c a
+
+instance Functor (Expr c) where
+    fmap f x = Pure f <*> x
+
+instance Applicative (Expr c) where
+    pure = Pure
+    (<*>) = App
+
+
+class Monoid (ExprDependency c) => ExprContext c where
+    type ExprDependency c :: Type
+
+
+getContext :: Expr c c
+getContext = GetContext
+
+
+addDependency :: ExprContext c => ExprDependency c -> Expr c a -> Expr c a
+addDependency = AddDependency
+
+collectDependencies :: ExprContext c => Expr c a -> ExprDependency c
+collectDependencies = \case
+    Pure {} -> mempty
+    App f x -> collectDependencies f <> collectDependencies x
+    GetContext {} -> mempty
+    AddDependency d x -> d <> collectDependencies x
+    ExprIO {} -> mempty
+
+
+exprIO :: IO a -> Expr c a
+exprIO = ExprIO
-- 
cgit v1.2.3