Forgot the attachment.
Romildo
--- Begin Message ---
On Mon, Jul 19, 2010 at 01:51:57PM -0400, Job Vranish wrote:
> Martijn van Steenbergen has a good blog post that describes the method I
> generally use:
> http://martijn.van.steenbergen.nl/journal/2010/06/24/generically-adding-position-information-to-a-datatype/
>
> In his example he annotates the expression tree with position information,
> but you can use the same method to add type annotations, or whatever you
> want.
After a quick read at Martijn blog article I've written the attached
test program, which works.
But I am not succeeding in deriving Show for the data types. Any help?
Romildo
> 2010/7/19 José Romildo Malaquias <j.romi...@gmail.com>
>
> > Hello.
> >
> > In his book "Modern Compilder Implementation in ML", Appel presents a
> > compiler project for the Tiger programming language where type checking
> > and intermediate code generation are intrinsically coupled.
> >
> > There is a function
> >
> > transExp :: Absyn.Exp -> (Tree.Exp,Types.Type)
> >
> > that do semantic analysis, translating an expression to the Tree
> > intermediate representation language and also do type checking,
> > calculating the type of the expression.
> >
> > Maybe the compiler can be made more didatic if these phases are separate
> > phases of compilation.
> >
> > The type checker would annotate the abstract syntax tree (ast) with type
> > annotations, that could be used later by the translater to intermediate
> > representation.
> >
> > In an imperative language probably each relevant ast node would have a
> > field for the type annotation, and the type checker would assign the
> > type of the node to this field after computing it.
> >
> > I am writing here to ask suggestions on how to annotate an ast with
> > types (or any other information that would be relevant in a compiler
> > phase) in Haskell.
> >
> > As an example, consider the simplified ast types:
> >
> > data Exp
> > = IntExp Integer
> > | VarExp Symbol
> > | AssignExp Symbol Exp
> > | IfExp Exp Exp (Maybe Exp)
> > | CallExp Symbol [Exp]
> > | LetExp [Dec] Exp
> >
> > data Dec
> > = TypeDec Symbol Ty
> > | FunctionDec Symbol [(Symbol,Symbol)] (Mybe Symbol) Exp
> > | VarDec Symbol (Maybe Symbol) Exp
> >
> > Expressions can have type annotations, but declarations can not.
> >
> > Comments?
--- End Message ---
module Main where
newtype Fix f = In { out :: f (Fix f) }
newtype AnnFix x f = AnnFix { runAnnFix :: (x, f (AnnFix x f)) }
data ExpF r
= Num Integer
| Add r r
| Mul r r
| If r r r
type BareExp = Fix ExpF
eval :: BareExp -> Integer
eval (In (Num i)) = i
eval (In (Add x y)) = eval x + eval y
eval (In (Mul x y)) = eval x * eval y
eval (In (If t x y)) | eval t == 0 = eval y
| otherwise = eval x
e = In (Add (In (Num 7)) (In (Num 8)))
type Pos = Int
type PosExp = AnnFix Pos ExpF
aEval (AnnFix (_, e)) =
case e of
Num i -> i
Add x y -> aEval x + aEval y
Mul x y -> aEval x * aEval y
If t x y | aEval t == 0 -> aEval y
| otherwise -> aEval x
ae = AnnFix (3, Add (AnnFix (1, Num 7)) (AnnFix (5, Num 8)))
main = do print (eval e)
print (aEval ae)
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