<p><font color="#3333ff"><font size="4">Hi! I am getting more problems with compilation. The two files where the problem occurs (a bit more of a general case of the sample of a few hours ago) are:</font></font></p><font color="#3333ff"><font size="4">
<p><br>-------------------------------------------------<br>--------------------Methods.hs-------------------<br>-------------------------------------------------<br>{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances,<br>
UndecidableInstances, FlexibleContexts, EmptyDataDecls, ScopedTypeVariables,<br> TypeOperators, TypeSynonymInstances #-}</p>
<p>module Methods where</p>
<p> import Records<br> import References</p>
<p> class Converter a rec_a where convert :: a -> rec_a</p>
<p> data Method s a b = Method (s -> a -> (b,s))</p>
<p> (<<-) :: forall rec_a s a b c n . (CNum n, HasField n (b->(c,a)) (rec_a), Converter a rec_a) => (Reference s (rec_a)) -> n -> Method s b c<br> (<<-) r n =<br> Method(\s -> \(x :: b) -><br>
let (v,s') = getter r s :: (rec_a,s)<br> m = v .! n :: (b -> (c,a))<br> (y,v') = m x :: (c, a)<br> v'' = convert v' :: rec_a<br> ((),s'') = setter r s' v''<br>
in (y,s''))</p>
<p><br> (.!!) :: Method s a b -> a -> Reference s b<br> (Method m) .!! x = from_constant (Constant (\s -> m s x))</p>
<p><br>-------------------------------------------------<br>---------------------Main.hs---------------------<br>-------------------------------------------------<br>{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances,<br>
UndecidableInstances, FlexibleContexts, EmptyDataDecls, ScopedTypeVariables,<br> TypeOperators, TypeSynonymInstances #-}</p>
<p>--module Main where</p>
<p>import Records<br>import References<br>import ReferenceMonad<br>import Methods</p>
<p>val = firstLabel<br>incr = nextLabel val</p>
<p>instance Converter RecCounter (Counter RecCounter) where <br> convert (RecCounter r) = r</p>
<p>type Counter k = (Integer :* (() -> ((),k)) :* EmptyRecord)<br>data RecCounter = RecCounter (Counter RecCounter)</p>
<p>mk_test :: Integer -> RecCounter<br>mk_test i = <br> RecCounter( val .= i<br> .* incr .= (\() -> ((), mk_test (i+1)))<br> .* EmptyRecord)</p>
<p>RecCounter test' = mk_test 0</p>
<p><br>res2 :: Reference (Counter RecCounter) Integer<br>res2 = do (this <<- incr :: Method (Counter RecCounter) () ()) .!! ()<br> v <- (this <-- val)<br> return v</p>
<p>count = fst (getter res2 test')</p>
<p> </p>
<p>Whenever I try to compile I get the following error:</p>
<p>*Methods> :load Main.hs<br>[1 of 5] Compiling Records ( Records.hs, interpreted )<br>[2 of 5] Compiling References ( References.hs, interpreted )<br>[3 of 5] Compiling ReferenceMonad ( ReferenceMonad.hs, interpreted )<br>
[4 of 5] Compiling Methods ( Methods.hs, interpreted )<br>[5 of 5] Compiling Main ( Main.hs, interpreted )</p>
<p>Main.hs:55:11:<br> No instances for (HasField<br> Z (() -> ((), a)) (AddField (() -> ((), RecCounter)) Emp<br>tyRecord),<br> Converter a (Counter RecCounter))<br> arising from a use of `<<-' at Main.hs:55:11-23<br>
Possible fix:<br> add an instance declaration for<br> (HasField<br> Z (() -> ((), a)) (AddField (() -> ((), RecCounter)) EmptyRecord),<br> Converter a (Counter RecCounter))<br> In the first argument of `(.!!)', namely<br>
`(this <<- incr :: Method (Counter RecCounter) () ())'<br> In a stmt of a 'do' expression:<br> (this <<- incr :: Method (Counter RecCounter) () ()) .!! ()<br> In the expression:<br>
do (this <<- incr :: Method (Counter RecCounter) () ()) .!! ()<br> v <- (this <-- val)<br> return v<br>Failed, modules loaded: Methods, References, Records, ReferenceMonad.<br>*Methods></p>
<p><br>Any hints?</p>
<p>PS: just to give some perspective on the code: I am putting together a system for expressing mutable objects through monads. I could provide the rest of my code in case of need :)<br clear="all"></p></font></font><br>
-- <br>Giuseppe Maggiore<br>Ph.D. Student (Languages and Games)<br>Microsoft Student Partner<br>Mobile: +393319040031<br>Office: +390412348444<br><br><br>