From ab4b56dcd8a24e757ef6534f4321c62e01eb0c95 Mon Sep 17 00:00:00 2001
From: Rick Winfrey <rewinfrey@github.com>
Date: Thu, 17 Nov 2016 16:17:09 -0600
Subject: [PATCH] Add FDoc.RecursionSchemes and anamorphism example

---
 src/FDoc/RecursionSchemes.hs | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 src/FDoc/RecursionSchemes.hs

diff --git a/src/FDoc/RecursionSchemes.hs b/src/FDoc/RecursionSchemes.hs
new file mode 100644
index 000000000..7ee53dbe8
--- /dev/null
+++ b/src/FDoc/RecursionSchemes.hs
@@ -0,0 +1,33 @@
+{-# LANGUAGE DataKinds, ScopedTypeVariables, TypeFamilies, TypeOperators #-}
+module FDoc.RecursionSchemes where
+
+import Data.Record
+import Range
+import Category
+import Term
+import Syntax
+import Prologue
+import Prelude
+import Data.Functor.Foldable hiding (ListF)
+import FDoc.Term
+
+data NewField = NewField deriving (Show)
+
+{-
+Anamorphism
+
+ana :: (a -> Base t a) -- ^ a (Base t)-coalgebra
+    -> a               -- ^ seed
+    -> t               -- ^ resulting fixed point
+
+Anamorphism as a recursion scheme "builds up" a recursive structure.
+Anamorphisms work by using a coalgebra, which maps a seed value to a fixed point structure.
+
+The example below adds a new field to the `Record` fields.
+
+-}
+
+indexedTermAna :: [leaf] -> Term (Syntax leaf) (Record '[NewField, Range, Category])
+indexedTermAna childrenLeaves = ana coalgebra (indexedTerm childrenLeaves)
+  where
+    coalgebra term = (NewField .: (extract term)) :< (unwrap term)