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Feedback and Gotchas

  • hs sig vs. lh sig

  • module and import story

  • inline

  • Binders: If I enter the following specification:

{-@ plus :: v1:Sparse a
         -> {v2:Sparse a | spDim v1 == spDim v2}
         -> {v3:Sparse a | spDim v3 == spDim v2 && spDim v3 == spDim v1}
     @-}

LH tells me that v2 is unbound. I feel that it should not be given that I defined v2 in the second argument to the spec.

  • Ch4 refined datatypes p35

    All types should derive Show so that a reader following along can try functions in GHCI and get a result printed

  • Pattern matching gives you invariants but raw field access doesn't. See Chris's note on 4.6 4.6)I came up with:

del :: (Ord a) => a -> BST a -> BST a
del k' t@(Node k l r)
 | k' < k = Node k (del k' l) r
 | k' > k = Node k l (del k' r)
 | otherwise = remv t
 where
  remv :: (Ord a) => BST a -> BST a
  remv (Node _ Leaf Leaf) = Leaf
  remv (Node _ l Leaf) = l
  remv (Node _ Leaf r) = r
  remv (Node _ l r) = Node iSuccE l iSuccR
  where
   iSuccE = mElt $ delMin r
   iSuccR = rest $ delMin r

However, LH complains about iSuccR. I don't see why it should have a problem with that given that iSuccR is the rest of the right tree which is by definition greater than iSuccE, which is the smallest element of the right tree. I imagine I could walk the entire right tree to verify this to please LH like I did with quickSort, but I can't imagine that is the correct answer.

  • in addition to the usual syntax:
     {-@ unsafeLookup :: n:Nat ->  {v:Vector a | n < (vlen v)} -> a @-}
  • could we get a "function" syntax:
     {-@ unsafeLookup :: n:Nat ->  v:Vector a -> a
         unsafeLookup n v = n < vlen v @-}

...or...

     {-@ unsafeLookup :: n:Int -> v:Vector a -> a
         unsafeLookup n v = n >= 0 && n < vlen v @-}

...or...

     {-@ unsafeLookup :: n:Int -> {v:Vector a | n < (vlen v)} -> a
         unsafeLookup n v = n >= 0 @-}
  • the "function" could take as arguments symbols that were bound in the "signature." It could take a partial specification and implement additional refinements. It "looks like Haskell" and allows the programmer more freedom in how they define their refinements