Lazy bind...

[Ken Shan]

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On 2002-07-30T18:43:28+0100, MR K P SCHUPKE wrote:
> The data types I used are:
>=20
> data (Error e) =3D> Reply e s a=3D Ok [s] a | Empty | Fail e
> data (Error e) =3D> Result e s a =3D Accepted (Reply e s a) | Rejected
>=20
> newtype (Error e) =3D> Parser e s a =3D Parser {runParser :: [s] -> Resul=
t e s a}
>=20
> newtype (Error e,Monad m) =3D> ParserT e s m a =3D ParserT {runParserT ::=
 [s] ->
> m (Result e s a)}
>=20
> [...]
>=20
>     Hope this makes things clearer...

Yes!  Let me rephrase my earlier suggestion in terms of these actual
types.

For reasons that will soon become clear, let me begin by rearranging
Result a bit:

    data Result x =3D Accepted x | Rejected
    newtype (Error e) =3D> Parser e s a
	=3D Parser {runParser :: [s] -> Result (Reply e s a)}
    newtype (Error e, Monad m) =3D> ParserT e s m a
	=3D ParserT {runParserT :: [s] -> m (Result (Reply e s a))}

(Here I have removed the constraint "Error e" from the definition of
Result.  I don't think it will cause you much trouble.)

Now, what about the following alternative definition of ParserT?

    newtype (Error e, Monad m) =3D> ParserT e s m a
	=3D ParserT {runParserT :: [s] -> m (Result (m (Reply e s a)))}

Would it suit your purposes?

--=20
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