Re: poll: polymorphic let bindings in do

[Marcin 'Qrczak' Kowalczyk]

Sun, 4 Jun 2000 11:02:20 -0700, Levent Erkok <[EMAIL PROTECTED]> pisze:

> Yes, we're working on a new semantics for do, where you'll be able 
> to bind variables recursively. For instance:
>  
>                  do xs <- Just (1:xs)
>                     return (take 5 xs)

Ah, like:

import MonadFix -- Andy Gill's module, present in GHC.

...
    do
        xs <- mfix $ \xs -> Just (1:xs)
        return (take 5 xs)

The Monad class would have a kind of the mfix method, right?

> But a let-generator will be visible everywhere:
> 
>   do ....                  -+
>      ....                   |
>      let f = ...            |>   f is visible everywhere (but is monomorphic)
>      ....                   |
>      ....                  -+
>     
> but it will not be polymorphic.

And "<-"-bound variables would be visible everywhere too?

I'm curious how the generic translation into mfix could look like if
everything is visible everywhere, e.g.:
    do
        a <- f1 b
        b <- f2 a
        return (a,b)

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