On Monday, February 10, 2014 3:40:35 AM UTC-5, Danny Navarro wrote:
Assuming most new users will be using `zoom` and `view` initially,
> would it be feasible to implement dummy versions for just `zoom` and
> `view` with more concrete types? They could be recommended for
> debugging and learning but should be replaced in real code.
>
I wondered about this yesterday, thinking that `zoom`, `view` and maybe
`over`
are the only essential operations. But with e.g.
pview :: Monad m
=> FoldLike' (Producer b m s) (Producer a m r) (Producer b m s)
-> Producer a m r -> Producer b m s
pview = view
pzoom :: Monad m
=> LensLike' (Zooming m c) (Producer a m r) (Producer b m s)
-> StateT (Producer b m s) m c -> StateT (Producer a m r) m c
pzoom = zoom
the first few lines of the error message tended
to be a little better, but these would
be followed by the familiar explosion unpacking
the synonyms for `Producer` and `LensLike`.
(I sort of favor exporting something like these since
it is in any case odd to have to decide amongst
libraries in order to apply a function to an argument)
I worried about this when the lenses were first
introduced, but after Gabriel's wonderful parsing
tutorial, it seemed to me that it was obviously
worth it. Now I don't know what to think.
It did occur to me that if one backs up a
little it might seem like plain common sense
that the lenses belong in separate associated
modules. No one would recommend a global
replacement of `fst` by `_1` , and similarly
in other cases, especially given the type `_1`
has in Control.Lens.
One problem with this is that it is pretty clear
that the use of the lenses with zoom is an
essential ingredient of the parser concept
Gabriel is explaining. One wouldn't want to
duplicate each function, once for operating
on Producers and again for operating on
StateT (Producers ...)
Michael
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