2010/7/19 José Romildo Malaquias <j.romildo@gmail.com>

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?

Indeed I would suggest the method described in our paper:

Martijn van Steenbergen, José Pedro Magalhães, and Johan Jeuring. Generic selections of subexpressions.
Paper link: http://dreixel.net/research/pdf/gss_draft.pdf
Related hackage package: http://hackage.haskell.org/package/Annotations

Something like what Malcolm proposed (adding one extra constructor) would also be possible generically, but it would be more similar to how we add meta-variables in our generic rewriting library (ask for more details if you're interested in this alternative).

Cheers,
Pedro

Regards,

Romildo
--
Computer Science Department
Universidade Federal de Ouro Preto, Brasil
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