On 5/4/06, Donald Bruce Stewart <[EMAIL PROTECTED]> wrote:
geoffw:
>
> I have an application written in OCaml that I'm interested in
> porting over to Haskell, and I was wondering what the best way to
replace
> the following OCaml function would be:
>
> Toploop.initialize_toplevel_env();;
>
> let eval txt = let lb = (Lexing.from_string txt) in
> let phr = !Toploop.parse_toplevel_phrase lb in
> Toploop.execute_phrase true Format.std_formatter phr;;
>
> eval "let add1 x = x +1;;";;
> eval "add1 2;;";;
>
> Where I would like to be able to "eval" Haskell-code instead. It looks
> like I might be able to achieve something like this using hs-plugins,
> but it looks a bit more complex. Is hs-plugins the best choice for this
> kind of "meta"-programming? I'm pretty sure Template Haskell will not
> work for me, at least as I understand it I can only manipulate program
> fragments that will be compiled later and as such that it will not be
> possible to execute them until the next "phase".
You can do some forms of runtime metaprogrammign with hs-plugins, yes.
E.g.
Prelude System.Eval.Haskell> v <- eval "1 + 2 :: Int" [] :: IO (Maybe Int)
Prelude System.Eval.Haskell> v
Just 3
Prelude System.Eval.Haskell> mf <- eval "\\x -> x + 1 :: Int" [] :: IO (Maybe (Int
-> Int))
Prelude System.Eval.Haskell> let f = fromJust mf
Prelude System.Eval.Haskell> :t f
f :: Int -> Int
Prelude System.Eval.Haskell> f 7
8
So if your program critically relies on this its possible to do.
You can also use the GHC library:
Prelude> :m GHC
Prelude GHC> GHC.init (Just "/home/david/coding/haskell/ghc/usr/lib/ghc-6.5")
Prelude GHC> session <- newSession Interactive
Prelude GHC> setSessionDynFlags session =<< initPackages =<<
getSessionDynFlags session
Prelude GHC> setContext session [] [mkModule "Prelude"]
Prelude GHC> runStmt session "let add1 x = x + 1"
Prelude GHC> runStmt session "add1 2"
3
Prelude GHC> :q
Leaving GHCi.
--
Friendly,
Lemmih
_______________________________________________
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
