purescript-set-monad

Monad.purs

module Data.Set.Monad where

import Prelude
import Data.Set as S
import Data.Foldable
import Data.Tuple.Nested
import Unsafe.Coerce

-- data Set a where
--   Prim   :: (Ord a) => S.Set a -> Set a
--   Return :: a -> Set a
--   Bind   :: Set a -> (a -> Set b) -> Set b
--   Zero   :: Set a
--   Plus   :: Set a -> Set a -> Set a
-- https://hgiasac.github.io/posts/2018-12-18-PureScript-GADTs-Alternatives---Recap.html

data Set a 
  = Prim   (Ord a => S.Set a)
  | Return (a)
  | Bind   (forall b. (Set b) /\ (b -> Set a))
  | Zero   
  | Plus   (Set a) (Set a)

run :: forall a. (Ord a) => Set a -> S.Set a
run (Prim s)                           = s
run (Return a)                         = S.singleton a
run (Zero)                             = S.empty
run (Plus ma mb)                       = run ma `S.union` run mb
run (Bind (Prim s /\ f))               = foldl S.union S.empty (S.map (run <<< f) s)
run (Bind (Return a /\ f))             = run (f a)
run (Bind (Zero /\ _))                 = S.empty
run (Bind (Plus (Prim s) ma /\ f))     = run (Bind (unsafeCoerce $ Prim (s `S.union` run ma) /\ f))
run (Bind (Plus ma (Prim s) /\ f))     = run (Bind (unsafeCoerce $ Prim (run ma `S.union` s) /\ f))
run (Bind (Plus (Return a) ma /\ f))   = run (Plus (f a) (Bind (unsafeCoerce $ ma /\ f)))
run (Bind (Plus ma (Return a) /\ f))   = run (Plus (Bind (unsafeCoerce $ ma /\ f)) (f a))
run (Bind (Plus Zero ma /\ f ))        = run (Bind (unsafeCoerce $ ma /\ f))
run (Bind (Plus ma Zero /\ f ))        = run (Bind (unsafeCoerce $ ma /\ f))
run (Bind (Plus (Plus ma mb) mc /\ f)) = run (Bind (unsafeCoerce $ Plus ma (Plus mb mc) /\ f ))
run (Bind (Plus ma mb /\ f))           = run (Plus (Bind (unsafeCoerce $ ma /\ f)) (Bind (unsafeCoerce $ mb /\ f)))
run (Bind (Bind (ma /\ f) /\ g))       = run (Bind (unsafeCoerce $ ma /\ (\a -> Bind (unsafeCoerce $ (f a) /\ g))))

-- Compiling Data.Set.Monad
-- Error found:

-- in module Data.Set.Monad
-- at src/Data/Set/Monad.purs:29:12 - 29:23 (line 29, column 12 - line 29, column 23)

--   Could not match constrained type
                                           
--     Ord b1 => Tuple (Set b1) (b1 -> Set a0)
                                           
--   with type
               
--     Tuple t2 t3
               

-- while trying to match type Ord b1 => Tuple (Set b1) (b1 -> Set a0)
--   with type Tuple t2 t3
-- while checking that expression case $0 of                                                   
--                                  (Prim s) -> s                                              
--                                  (Return a) -> singleton a                                  
--                                  Zero -> empty                                              
--                                  (Plus ma mb) -> (union (...)) (run mb)                     
--                                  (Bind (Tuple (Prim s) f)) -> ((...) empty) ((...) s)       
--                                  (Bind (Tuple (Return a) f)) -> run (f a)                   
--                                  (Bind (Tuple Zero _)) -> empty                             
--                                  (Bind (Tuple (Plus (Prim s) ma) f)) -> run (Bind (...))    
--                                  (Bind (Tuple (Plus ma (Prim s)) f)) -> run (Bind (...))    
--                                  (Bind (Tuple (Plus (Return a) ma) f)) -> run ((...) (...)) 
--                                  (Bind (Tuple (Plus ma (Return a)) f)) -> run ((...) (...)) 
--                                  (Bind (Tuple (Plus Zero ma) f)) -> run (Bind (...))        
--                                  (Bind (Tuple (Plus ma Zero) f)) -> run (Bind (...))        
--                                  (Bind (Tuple (Plus (Plus ma mb) mc) f)) -> run (Bind (...))
--                                  (Bind (Tuple (Plus ma mb) f)) -> run ((...) (...))         
--                                  (Bind (Tuple (Bind (Tuple ma f)) g)) -> run (Bind (...))   
--   has type Set a0
-- in binding group run

-- where a0 is a rigid type variable
--         bound at (line 0, column 0 - line 0, column 0)
--       b1 is a rigid type variable
--         bound at (line 20, column 13 - line 20, column 55)
--       t2 is an unknown type
--       t3 is an unknown type

-- See https://github.com/purescript/documentation/blob/master/errors/ConstrainedTypeUnified.md for more information,
-- or to contribute content related to this error.


-- [error] Failed to build.