----------------------------------------------------------------
-- unify.phs
--   contains the polytypic part of the unification algorithm
--     (i.e. almost nothing)
-- To test this: see README.txt
module PolyUnify where
import Base(inn,out,fmap2)
import Flatten(fflatten)
import Equal(fequal)
----------------------------------------------------------------
--instance Regular d => Children (d a) where
--  children    = children'
--  mapChildren = mapChildren'
children'      = fflatten . fmap2 nil singleton . out
mapChildren' f = inn      . fmap2 id  f         . out

--instance (Regular d, Eq a) => TopEq (d a) where
--  topEq = topEq'
topEq' t t' = fequal (==) (\_ _ -> True) (out t) (out t')

----------------------------------------------------------------
-- all the examples have the variable as their first constructor
varCheck' = fvarCheck' . out
polytypic fvarCheck' :: f a b -> Maybe Int
  = case f of
      g + h      ->  either fvarCheck' err
      Const Int  ->  ok
      g          ->  err

ok  = Just 
err = const Nothing