now (+) in the abstract syntax works, i.e. it knows how to deal with partial sums

src/runtime/haskell/PGF/Binary.hs

@@ -177,7 +177,11 @@ instance Binary Instr where
   put (DROP n             ) = putWord8 64  >> put n
   put (JUMP l             ) = putWord8 68  >> put l
   put (FAIL               ) = putWord8 72
-  put (ADD                ) = putWord8 76
+  put (PUSH_ACCUM (LInt n)) = putWord8 76 >> put n
+  put (PUSH_ACCUM (LStr s)) = putWord8 77 >> put s
+  put (PUSH_ACCUM (LFlt d)) = putWord8 78 >> put d
+  put (POP_ACCUM          ) = putWord8 80
+  put (ADD                ) = putWord8 84
 
 instance Binary Type where
   put (DTyp hypos cat exps) = put (hypos,cat,exps)

src/runtime/haskell/PGF/ByteCode.hs

@@ -32,6 +32,8 @@ data Instr
   | DROP {-# UNPACK #-} !Int
   | JUMP {-# UNPACK #-} !CodeLabel
   | FAIL
+  | PUSH_ACCUM Literal
+  | POP_ACCUM
   | ADD
 
 data IVal
@@ -71,6 +73,8 @@ ppInstr (TUCK v n       ) = text "TUCK       " <+> ppIVal v <+> int n
 ppInstr (DROP n         ) = text "DROP       " <+> int n
 ppInstr (JUMP l         ) = text "JUMP       " <+> ppLabel l
 ppInstr (FAIL           ) = text "FAIL"
+ppInstr (PUSH_ACCUM  lit) = text "PUSH_ACCUM " <+> ppLit lit
+ppInstr (POP_ACCUM      ) = text "POP_ACCUM"
 ppInstr (ADD            ) = text "ADD"
 
 ppIVal (HEAP     n) = text "hp"  <> parens (int n)