From 2accf5c3814c843bbfb6733f7fd245cee5415dbd Mon Sep 17 00:00:00 2001
From: Jaro Reinders <jaro.reinders@gmail.com>
Date: Thu, 27 Jul 2023 15:23:02 +0200
Subject: [PATCH] Add experiment1

---
 experiments/Experiment1.hs | 141 +++++++++++++++++++++++++++++++++++++
 gigaparsec.cabal           |  15 ++--
 2 files changed, 151 insertions(+), 5 deletions(-)
 create mode 100644 experiments/Experiment1.hs

diff --git a/experiments/Experiment1.hs b/experiments/Experiment1.hs
new file mode 100644
index 0000000..068fd43
--- /dev/null
+++ b/experiments/Experiment1.hs
@@ -0,0 +1,141 @@
+{-# OPTIONS_GHC -Wall #-}
+{-# LANGUAGE GADTs, Arrows #-}
+
+import Prelude hiding (id, (.))
+import Control.Category
+import Control.Arrow
+
+data Parser' p a b where
+  Id :: Parser' p a a
+  Arr :: (a -> x) -> Parser p x b -> Parser' p a b
+  Port :: Parser p a1 x -> Parser p (Either x a2, a3) b -> Parser' p (Either a1 a2, a3) b
+  Match :: Char -> Parser p a b -> Parser' p a b
+  Free :: p (Parser p) a1 x -> Parser p (x, a2) b -> Parser' p (a1, a2) b
+
+instance Category (Parser' p) where
+  id = Id
+  k . Id = k 
+  k . (Match c p) = Match c (Parser [k] . p)
+  k . (Arr f p) = Arr f (Parser [k] . p)
+  k . (Port p q) = Port p (Parser [k] . q)
+  k . (Free x p) = Free x (Parser [k] . p)
+
+assocr :: ((a,b),c) -> (a,(b,c))
+assocr ((a,b),c) = (a,(b,c))
+
+assocl :: (a,(b,c)) -> ((a,b),c)
+assocl (a,(b,c)) = ((a,b),c)
+
+instance Arrow (Parser' p) where
+  arr f = Arr f id
+  first Id = Id
+  first (Arr f k) = Arr (first f) (first k)
+  first (Port p k) = Arr assocr (Parser [Port p (Parser [Arr assocl (first k)])])
+  first (Match c k) = Match c (first k)
+  first (Free x k) = Arr assocr (Parser [Free x (Parser [Arr assocl (first k)])])
+
+newtype Parser p a b = Parser [Parser' p a b]
+
+instance ArrowZero (Parser p) where
+  zeroArrow = Parser []
+  
+instance ArrowPlus (Parser p) where
+  Parser ps <+> Parser qs = Parser (ps ++ qs)
+
+instance Category (Parser p) where
+  id = Parser [Id]
+  p0 . Parser qs = foldr (<+>) zeroArrow $ map (composeL p0) qs where
+    composeL k Id = k 
+    composeL k (Match c p) = Parser [Match c (k . p)]
+    composeL k (Arr f p) = Parser [Arr f (k . p)]
+    composeL k (Port p q) = Parser [Port p (k . q)]
+    composeL k (Free x p) = Parser [Free x (k . p)]
+
+instance Arrow (Parser p) where
+  arr f = Parser [Arr f id]
+  first (Parser ps) = Parser (map first ps)
+
+instance ArrowChoice (Parser p) where
+  left p = arr (,()) >>> Parser [Port p id] >>> arr fst
+
+char :: Char -> Parser p a a
+char c = Parser [Match c id]
+
+string :: String -> Parser p a a
+string [] = id
+string (x:xs) = char x >>> string xs
+
+send :: p (Parser p) a b -> Parser p a b
+send x = Parser [Arr (,()) (Parser [Free x (arr fst)])]
+
+parse :: forall p a b. (forall x y. p (Parser p) x y -> Parser p x y) -> p (Parser p) a b -> String -> a -> [b]
+parse g p0 xs0 x0 = map fst $ go x0 xs0 (g p0) where
+  go :: c -> String -> Parser p c d -> [(d, String)]
+  go x xs (Parser ps) = go' x xs =<< ps
+  go' :: c -> String -> Parser' p c d -> [(d, String)] 
+  go' x xs Id = [(x, xs)]
+  go' x xs (Arr f k) = go (f x) xs k
+  go' y (x:xs) (Match c k) | x == c = go y xs k
+  go' _ _ Match{} = []
+  go' x xs (Port p k) =
+    case x of
+      (Left x1,y) -> do
+        (x', xs') <- go x1 xs p
+        go (Left x', y) xs' k
+      (Right x2, y) -> go (Right x2, y) xs k
+  go' x xs (Free p k) =
+    case x of
+      (x', y) -> go x' xs (k . arr (,y) . g p) -- TODO avoid left-recursion
+
+-- E(l,r) ::= [4 >= l] '-' E(l,4) //4
+-- | [3 >= r, 3 >= l] E(3,3) '*' E(l,4) //3
+-- | [2 >= r, 2 >= l] E(2,2) '+' E(l,3) //2
+-- | [1 >= l] 'if' E(0,0) 'then' E(0,0) 'else' E(0,0) //1
+-- | a
+
+guardA :: (ArrowChoice a, ArrowZero a) => a Bool ()
+guardA = proc b ->
+  if b
+  then returnA -< ()
+  else zeroArrow -< ()
+
+data E p a b where
+  E :: E p (Int, Int) Expr
+
+data Expr = Neg Expr | Mul Expr Expr | Add Expr Expr | ITE Expr Expr Expr | A
+  deriving Show
+
+gram :: E p a b -> Parser E a b
+gram E =
+  proc (l, r) -> do
+    guardA -< 4 >= l
+    char '-' -< ()
+    x <- send E -< (l, 4)    
+    returnA -< Neg x
+  <+> do
+    guardA -< 3 >= r && 3 >= l
+    x <- send E -< (3, 3)
+    char '*' -< ()
+    y <- send E -< (l, 4)
+    returnA -< Mul x y
+  <+> do
+    guardA -< 2 >= r && 2 >= l
+    x <- send E -< (2, 2)
+    char '+' -< ()
+    y <- send E -< (l, 3)
+    returnA -< Add x y
+  <+> do
+    guardA -< 1 >= l
+    string "if" -< ()
+    b <- send E -< (0, 0)
+    string "then" -< ()
+    x <- send E -< (0, 0)
+    string "else" -< ()
+    y <- send E -< (0, 0)
+    returnA -< ITE b x y
+  <+> do
+    char 'a' -< ()
+    returnA -< A
+
+main :: IO ()
+main = gram `seq` pure ()
\ No newline at end of file
diff --git a/gigaparsec.cabal b/gigaparsec.cabal
index 9568bd9..3c32cfb 100644
--- a/gigaparsec.cabal
+++ b/gigaparsec.cabal
@@ -42,8 +42,13 @@ executable gpc-examples
     build-depends:    gigaparsec
 
 test-suite gpc-test
-  import:             common
-  type:               exitcode-stdio-1.0
-  hs-source-dirs:     tests
-  main-is:            test.hs
-  build-depends:      tasty, tasty-hunit, gigaparsec
\ No newline at end of file
+    import:           common
+    type:             exitcode-stdio-1.0
+    hs-source-dirs:   tests
+    main-is:          test.hs
+    build-depends:    tasty, tasty-hunit, gigaparsec
+
+executable gpc-experiment1
+    import:           common
+    main-is:          Experiment1.hs
+    hs-source-dirs:   experiments