arianvp / generics-mrsop-diff

Typesafe structural diffing of haskell datratypes using generics

generics-mrsop-diff

thesis.pdf

generics-mrsop-diff's Issues

Impossible to pattern match on Ctxs and discover _what_ constructor it is pointing to

Given the definition of Ctxs:

data Ctx :: (kon -> *) -> [*] -> [[Atom kon]] -> Nat -> * where
  Ctx :: Constr c n
      -> NPHole ki fam ix (Lkup n c)
      -> Ctx ki fam c ix
data Ctxs :: (kon -> *) -> [*] -> [[[Atom kon]]] -> Nat -> Nat -> * where
  Nil  :: Ctxs ki fam cs ix ix
  Cons :: (IsNat ix , IsNat a , IsNat b)
       => Ctx ki fam (Lkup ix cs) b -> Ctxs ki fam cs a ix
       -> Ctxs ki fam cs a b

and me wanting to visualize the Constructor the hole is pointing to

We will need to somehow call :

  datatypeInfo :: (IsNat ix)
               => Proxy fam -> SNat ix -> DatatypeInfo (Lkup ix codes)

However, When we pattern match on Cons, and want to call datatypeInfo,
How do we ever discover the SNat ix that we need to supply? Because
ix is existential in Ctxs we can't call getSNat (Proxy :: Proxy ix)

So there is no what for us to visualize the Constructor inside Ctx

case ctxs of
  Nil -> ""
  Cons (Ctx c h) ctxs ->  
    constructorName (constrInfoLkup c (datatypeInfo (Proxy :: Proxy fam)) ????)

Type error while trying to visualize Zippers

I'm trying to deconstruct and pattern match on a Ctxs and Ctx in order to visualize a zipper, but Haskell is giving me a hard time.

generics-mrsop-diff/src/Generics/MRSOP/GraphViz/Zipper.hs

Lines 32 to 45 in a930839

	visualizeNPHole ::
	(IsNat ix, Show1 ki, sum ~ Lkup ix codes, prod ~ Lkup n sum)
	=> Constr sum n
	-> NPHole ki fam ix prod
	-> [DotSM NodeId]
	visualizeNPHole c (H poa) =
	freshNode [toLabel "*"] :
	elimNP (elimNA (\k -> freshNode [toLabel (show k)]) undefined) poa
	visualizeNPHole c (T a h) =
	let elimK k = freshNode [toLabel (show k)]
	-- we don't visualize recursion for now, clutters tree
	elimI i = freshNode [toLabel "..."]
	in
	elimNA elimK elimI a : visualizeNPHole c h

gives the following type error:

    /home/arian/Documents/UU/Thesis/generics/generics-mrsop-diff/src/Generics/MRSOP/GraphViz/Zipper.hs:33:6: error:
        • Could not deduce: Lkup ix codes0 ~ sum
          from the context: (IsNat ix, Show1 ki, sum ~ Lkup ix codes,
                             prod ~ Lkup n sum)
            bound by the type signature for:
                       visualizeNPHole :: forall kon1 (ix :: Nat) (ki :: kon1
                                                                         -> *) (sum :: [[Atom
                                                                                           kon1]]) (codes :: [[[Atom
                                                                                                                  kon1]]]) (prod :: [Atom
                                                                                                                                       kon1]) (n :: Nat) (fam :: [*]).
                                          (IsNat ix, Show1 ki, sum ~ Lkup ix codes,
                                           prod ~ Lkup n sum) =>
                                          Constr sum n -> NPHole ki fam ix prod -> [DotSM NodeId]
            at src/Generics/MRSOP/GraphViz/Zipper.hs:(33,6)-(36,19)
          ‘sum’ is a rigid type variable bound by
            the type signature for:
              visualizeNPHole :: forall kon1 (ix :: Nat) (ki :: kon1
                                                                -> *) (sum :: [[Atom
                                                                                  kon1]]) (codes :: [[[Atom
                                                                                                         kon1]]]) (prod :: [Atom
                                                                                                                              kon1]) (n :: Nat) (fam :: [*]).
                                 (IsNat ix, Show1 ki, sum ~ Lkup ix codes, prod ~ Lkup n sum) =>
                                 Constr sum n -> NPHole ki fam ix prod -> [DotSM NodeId]
            at src/Generics/MRSOP/GraphViz/Zipper.hs:(33,6)-(36,19)
        • In the ambiguity check for ‘visualizeNPHole’
          To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
          In the type signature:
            visualizeNPHole :: (IsNat ix,
                                Show1 ki,
                                sum ~ Lkup ix codes,
                                prod ~ Lkup n sum) =>
                               Constr sum n -> NPHole ki fam ix prod -> [DotSM NodeId]
       |
    33 |      (IsNat ix, Show1 ki, sum ~ Lkup ix codes, prod ~ Lkup n sum)
       |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...