[Haskell-cafe] MonadFix wiki confusion

[Levent Erkok]

Hi Samuel:

You are correct that the lazy construction of the tuple is crucial in
tying-the-monadic-knot. However, the point about making the BTree
constructors strict is still interesting, as it pertains to delayed use of
recursive values, rather than how they are represented/stored. The
situation is really no different than a regular recursive let-expression in
a non-monadic context.

Of course, it would still be fine to update the text to make that point
clear like you suggested, should you be so inclined!

-Levent.

On Sun, Oct 18, 2015 at 7:40 AM, Samuel Rødal <srodal at gmail.com> wrote:

> Hello,
>
> the MonadFix wiki at https://wiki.haskell.org/MonadFix has a statement
> that I feel is a bit misleading.
>
> In section "2.2 Lazy algorithm interleaved with effects", it claims
> that making the BTree data structure strict doesn't cause endless
> recursion.
>
> Well, that's true, but that's just because rep_x_sum returns a tuple
> containing the BTree and the summed values of the current subtree, and
> the tuple is lazily constructed - postponing the construction of the
> tree value. So highlighting the fact that the function still works
> when the BTree structure is made strict is kind of a red herring.
>
> Maybe the confusion could be avoided by removing the part about making
> BTree strict, or adding a note about the tuple still ensuring lazy
> construction?
>
> --
> Samuel
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