From 2e5df1862200510ddd997e00e4f1d6b25c52db13 Mon Sep 17 00:00:00 2001
From: Jaro Reinders <jaro.reinders@gmail.com>
Date: Mon, 10 Apr 2023 16:03:06 +0200
Subject: [PATCH] Add data dependent experiment

---
 experiments/DataDependent.hs | 43 ++++++++++++++++++++++++++++++++++++
 gigaparsec.cabal             | 11 ++++++---
 2 files changed, 51 insertions(+), 3 deletions(-)
 create mode 100644 experiments/DataDependent.hs

diff --git a/experiments/DataDependent.hs b/experiments/DataDependent.hs
new file mode 100644
index 0000000..6c904fd
--- /dev/null
+++ b/experiments/DataDependent.hs
@@ -0,0 +1,43 @@
+{-# LANGUAGE DeriveFunctor #-}
+import Control.Applicative
+import Data.Char
+
+newtype Parser s a = Parser { parse :: String -> s -> [(a, String, s)] } deriving Functor
+
+instance Applicative (Parser s) where
+  pure x = Parser $ \xs s -> [(x, xs, s)]
+  Parser p <*> Parser q = Parser $ \xs s -> do
+    (f, xs', s') <- p xs s
+    (x, xs'', s'') <- q xs' s'
+    pure (f x, xs'', s'')
+
+instance Alternative (Parser s) where
+  empty = Parser $ \_ _ -> []
+  Parser p <|> Parser q = Parser $ \xs s ->
+    p xs s ++ q xs s
+
+char :: Char -> Parser s Char
+char c = Parser $ \xs s ->
+  case xs of
+    c' : xs' | c == c' -> [(c, xs', s)]
+    _ -> []
+
+put :: Parser s' s -> Parser s a -> Parser s' a
+put (Parser p) (Parser q) = Parser $ \xs s -> do
+  (s', xs', _) <- p xs s
+  (x, xs'', _) <- q xs' s'
+  pure (x, xs'', s)
+
+modify :: (s -> [s]) -> Parser s ()
+modify f = Parser $ \xs s -> [((), xs, s') | s' <- f s]
+
+dependentReplicate :: Parser s Int -> Parser Int a -> Parser s [a]
+dependentReplicate p1 p2 = put p1 rest where
+  rest = (:) <$ modify (\s -> [s | s > 0]) <*> p2 <* modify (\s -> [s - 1]) <*> rest
+      <|> [] <$ modify (\s -> [s | s == 0])
+
+digit :: Parser s Int
+digit = asum [digitToInt <$> char (intToDigit i) | i <- [0..9]]
+
+main :: IO ()
+main = print $ parse (dependentReplicate digit (char '.')) "4...." ()
\ No newline at end of file
diff --git a/gigaparsec.cabal b/gigaparsec.cabal
index 08ec209..25491fe 100644
--- a/gigaparsec.cabal
+++ b/gigaparsec.cabal
@@ -20,8 +20,8 @@ description:
     I have also not put any effort in making this library performant yet.
 
 source-repository head
-  type:     git
-  location: https://github.com/noughtmare/gigaparsec
+    type:     git
+    location: https://github.com/noughtmare/gigaparsec
 
 common common
     build-depends:            base >= 4.14 && <5
@@ -40,4 +40,9 @@ executable gigaparsec-examples
     import:           common
     main-is:          Main.hs
     hs-source-dirs:           examples
-    build-depends:    gigaparsec
\ No newline at end of file
+    build-depends:    gigaparsec
+
+executable gigaparsec-experiments-datadependent
+    import:           common
+    main-is:          DataDependent.hs
+    hs-source-dirs:           experiments
\ No newline at end of file