From 6b6258f6325610543b888bbd7ed072c4a180a29e Mon Sep 17 00:00:00 2001
From: Anupam Jain <ajnsit@gmail.com>
Date: Wed, 6 Jan 2021 11:46:16 +0530
Subject: [PATCH] Initial working implementation

---
 src/Main.purs     | 10 ----------
 src/Typeable.js   | 42 ++++++++++++++++++++++++++++++++++++++++++
 src/Typeable.purs | 37 +++++++++++++++++++++++++++++++++++++
 test/Main.purs    | 33 ++++++++++++++++++++++++++++++---
 4 files changed, 109 insertions(+), 13 deletions(-)
 delete mode 100644 src/Main.purs
 create mode 100644 src/Typeable.js
 create mode 100644 src/Typeable.purs

diff --git a/src/Main.purs b/src/Main.purs
deleted file mode 100644
index 5c18dca..0000000
--- a/src/Main.purs
+++ /dev/null
@@ -1,10 +0,0 @@
-module Main where
-
-import Prelude
-
-import Effect (Effect)
-import Effect.Console (log)
-
-main :: Effect Unit
-main = do
-  log "🍝"
diff --git a/src/Typeable.js b/src/Typeable.js
new file mode 100644
index 0000000..15411b7
--- /dev/null
+++ b/src/Typeable.js
@@ -0,0 +1,42 @@
+exports.typerepImpl1 = function(t1) {
+  return t1;
+};
+
+exports.typerepImpl2 = function(t1) {
+  return function(t2) {
+    return [t1,t2];
+  };
+};
+
+exports.typerepImpl3 = function(t1) {
+    return function(t2) {
+        return function(t3) {
+            return [t1,t2,t3];
+        };
+    };
+};
+
+exports.eqTypeRep = function(t1) {
+    return function(t2) {
+        return nestedArrayEq(t1, t2);
+    };
+};
+
+exports.clog = function(a) {
+    return function() {
+        console.log("CLOG:", a);
+    };
+};
+
+function nestedArrayEq(t1, t2) {
+  if(Array.isArray(t1)) {
+      if(!(Array.isArray(t2) && (t1.length == t2.length)))
+          return false;
+      for (var i=0; i<t1.length;i++) {
+          if(!nestedArrayEq(t1[i], t2[i]))
+              return false;
+      }
+      return true;
+  }
+  return t1 === t2;
+}
diff --git a/src/Typeable.purs b/src/Typeable.purs
new file mode 100644
index 0000000..3ed2514
--- /dev/null
+++ b/src/Typeable.purs
@@ -0,0 +1,37 @@
+module Typeable where
+
+import Data.Unit (Unit)
+import Effect (Effect)
+
+-- Indexed Typereps
+data TypeRep a
+
+-- Typeable class
+class Typeable a where
+  typeRep :: TypeRep a
+
+-- Implementation detail
+-- Tagging types
+data Proxy1 a = Proxy1
+data Proxy2 (t :: Type -> Type) = Proxy2
+data Proxy3 (t :: Type -> Type -> Type) = Proxy3
+class Tag1 a where t1 :: Proxy1 a
+class Tag2 (a :: Type -> Type) where t2 :: Proxy2 a
+class Tag3 (a :: Type -> Type -> Type) where t3 :: Proxy3 a
+
+-- Constructors for the opaque data type
+foreign import typerepImpl1 :: forall a. Tag1 a => TypeRep a
+foreign import typerepImpl2 :: forall a b. Typeable b => Tag2 a => TypeRep (a b)
+foreign import typerepImpl3 :: forall a b c. Typeable c => Typeable b => Tag1 c => TypeRep (a b c)
+
+-- Type equality
+foreign import eqTypeRep :: forall a b. TypeRep a -> TypeRep b -> Boolean
+
+-- Common instances
+instance tag1Int :: Tag1 Int where t1 = Proxy1
+instance typeableInt :: Typeable Int where typeRep = typerepImpl1
+instance tag2Array :: Tag2 Array where t2 = Proxy2
+instance typeableArray :: Typeable a => Typeable (Array a) where typeRep = typerepImpl2
+
+-- DEBUG: Console.log anything
+foreign import clog :: forall a. a -> Effect Unit
diff --git a/test/Main.purs b/test/Main.purs
index f91f98c..5fc8ebd 100644
--- a/test/Main.purs
+++ b/test/Main.purs
@@ -3,9 +3,36 @@ module Test.Main where
 import Prelude
 
 import Effect (Effect)
-import Effect.Class.Console (log)
+import Typeable (class Tag1, class Tag2, class Typeable, Proxy1(..), Proxy2(..), TypeRep, clog, eqTypeRep, typeRep, typerepImpl1, typerepImpl2)
 
 main :: Effect Unit
 main = do
-  log "🍝"
-  log "You should add some tests."
+  clog (eqTypeRep (typeRep :: _ (Array Person)) typeArrPerson)
+  clog (eqTypeRep (typeRep :: _ (Array Person2)) typeArrPerson)
+  clog (eqTypeRep (typeRep :: _ (Optional Int)) (typeRepFromVal (Some 1)))
+  clog (eqTypeRep (typeRep :: _ (Optional Person)) (typeRepFromVal (Some 1)))
+  where
+    typeArrPerson :: TypeRep (Array Person)
+    typeArrPerson = typeRep
+
+
+newtype Person = Person { name :: String, location :: String }
+newtype Person2 = Person2 { name :: String, location :: String }
+
+-- Create Typeable instances for Person
+instance tag1Person :: Tag1 Person where t1 = Proxy1
+instance typeablePerson :: Typeable Person where typeRep = typerepImpl1
+
+-- Create Typeable instances for Person2
+instance tag1Person2 :: Tag1 Person2 where t1 = Proxy1
+instance typeablePerson2 :: Typeable Person2 where typeRep = typerepImpl1
+
+data Optional a = None | Some a
+
+-- Create Typeable instances for Person
+instance tag2Optional :: Tag2 Optional where t2 = Proxy2
+instance typeableOptional :: Typeable a => Typeable (Optional a) where
+  typeRep = typerepImpl2
+
+typeRepFromVal :: forall a. Typeable a => a -> TypeRep a
+typeRepFromVal _ = typeRep