WIP better zero/plus, fixing Accum (...)

The accumulator implementation was wrong because it forgot (in accumAdd)
to take into account that values may be variably-sized. Furthermore, it
was also complexity-inefficient because it did not build up a sparse
value. Thus let's go for the Haskell-interpreter-equivalent of what a
real, fast, compiled implementation would do: just a tree with mutable
variables. In practice one can decide to indeed flatten parts of that
tree, i.e. using a tree representation for nested pairs is bad, but that
should have been done _before_ execution and for _all_ occurrences of
that type fragment, not live at runtime by the accumulator
implementation.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/AST/Pretty.hs b/src/AST/Pretty.hs
index 2ce883b..f5e681a 100644
--- a/src/AST/Pretty.hs
+++ b/src/AST/Pretty.hs
@@ -181,6 +181,13 @@ ppExpr' d val = \case
     return $ showParen (d > 10) $
       showString ("accum " ++ show (unSNat i) ++ " ") . e1' . showString " " . e2' . showString " " . e3'
 
+  EZero _ -> return $ showString "zero"
+
+  EPlus _ a b -> do
+    a' <- ppExpr' 11 val a
+    b' <- ppExpr' 11 val b
+    return $ showParen (d > 10) $ showString "plus " . a' . showString " " . b'
+
   EError _ s -> return $ showParen (d > 10) $ showString ("error " ++ show s)
 
 ppExprLet :: Int -> SVal env -> Expr x env t -> M ShowS