PostOrder Traversal for Tree doesn't compile in Gibbon for the case where scalar is demanded out of order.

[vidsinghal]

Given the post order program, demanding val before recursing left and right children of tree in Node case doesn't work.

data Tree = Leaf Int | Node Tree Tree Int


mkTree :: Int -> Tree 
mkTree depth  = if depth <= 0 then 
                    Leaf depth 
                else 
                    let left  = mkTree (depth - 1)
                        right = mkTree (depth - 1)
                     in Node left right depth

sumTree :: Tree -> Int 
sumTree tree = case tree of 
      Leaf val -> val 
      Node left right val -> val + sumTree(left) + sumTree(right)

gibbon_main = sumTree (mkTree 10)

Get the following error:

gibbon: Var val_18_94_155 not found. Checking: 
: VarE "val_18_94_155"
CallStack (from HasCallStack):
  error, called at src/Gibbon/L3/Typecheck.hs:824:21 in gibbon-0.2-inplace:Gibbon.L3.Typecheck

However demanding the value in order works, following code works:

data Tree = Leaf Int | Node Tree Tree Int


mkTree :: Int -> Tree 
mkTree depth  = if depth <= 0 then 
                    Leaf depth 
                else 
                    let left  = mkTree (depth - 1)
                        right = mkTree (depth - 1)
                     in Node left right depth

sumTree :: Tree -> Int 
sumTree tree = case tree of 
      Leaf val -> val 
      Node left right val -> sumTree(left) + sumTree(right) + val

gibbon_main = sumTree (mkTree 10)