Comment L0's usage of holding type information in location fields

Author: jazullo

gibbon-compiler/src/Gibbon/L0/Syntax.hs

@@ -28,6 +28,7 @@ import           Gibbon.Language hiding (UrTy(..))
 
 --------------------------------------------------------------------------------
 
+-- In L0, type information may be held in locations, as locations don't exist
 type Exp0     = PreExp E0Ext Ty0 Ty0
 type DDefs0   = DDefs Ty0
 type DDef0    = DDef Ty0
@@ -41,6 +42,7 @@ type Prog0    = Prog Exp0
 data E0Ext loc dec =
    LambdaE [(Var,dec)] -- Variable tagged with type
            (PreExp E0Ext loc dec)
+   -- unused for much of L0, may be due to a bug
  | PolyAppE (PreExp E0Ext loc dec) -- Operator
             (PreExp E0Ext loc dec) -- Operand
  | FunRefE [loc] Var -- Reference to a function (toplevel or lambda),

gibbon-compiler/src/Gibbon/Language/Syntax.hs

@@ -361,6 +361,8 @@ data PreExp (ext :: Type -> Type -> Type) loc dec =
    | MkProdE   [EXP] -- ^ Tuple construction
    | ProjE Int EXP   -- ^ Tuple projection.
 
+     -- in L0, loc carries the type of the corresponding var
+     -- as there is no location information
    | CaseE EXP [(DataCon, [(Var,loc)], EXP)]
      -- ^ Case on a datatype.  Each bound, unpacked variable lives at
      -- a fixed, read-only location.